[PATCH v6 00/11] evm: Improve usability of portable signatures

EVM portable signatures are particularly suitable for the protection of
metadata of immutable files where metadata is signed by a software vendor.
They can be used for example in conjunction with an IMA policy that
appraises only executed and memory mapped files.

However, some usability issues are still unsolved, especially when EVM is
used without loading an HMAC key. This patch set attempts to fix the open
issues.

Patch 1 allows EVM to be used without loading an HMAC key. Patch 2 avoids
appraisal verification of public keys (they are already verified by the key
subsystem).

Patches 3-4 allow metadata verification to be turned off when no HMAC key
is loaded and to use this mode in a safe way (by ensuring that IMA
revalidates metadata when there is a change).

Patches 5-8 make portable signatures more usable if metadata verification
is not turned off, by ignoring the INTEGRITY_NOLABEL and INTEGRITY_NOXATTS
errors when possible, by accepting any metadata modification until
signature verification succeeds (useful when xattrs/attrs are copied
sequentially from a source) and by allowing operations that don't change
metadata.

Patch 9 makes it possible to use portable signatures when the IMA policy
requires file signatures and patch 10 shows portable signatures in the
measurement list when the ima-sig template is selected.

Lastly, patch 11 avoids undesired removal of security.ima when a file is
not selected by the IMA policy.

Test:
https://github.com/robertosassu/ima-evm-utils/blob/ima-evm-fixes-v6-devel-v1/tests/portable_signatures.test

Test results:
https://travis-ci.com/github/robertosassu/ima-evm-utils/jobs/503096506
https://travis-ci.com/github/robertosassu/ima-evm-utils/jobs/503096510


Changelog

v5:
- remove IMA xattr post hooks and call evm_revalidate() from pre hooks
  (suggested by Mimi)
- rename evm_ignore_error_safe() to evm_hmac_disabled() and check the errors
  inline (suggested by Mimi)
- improve readability of error handling in evm_verify_hmac() (suggested by Mimi)
- don't show an error message if the EVM status is INTEGRITY_PASS_IMMUTABLE
  (suggested by Mimi)
- check if CONFIG_FS_POSIX_ACL is defined in evm_xattr_acl_change() (reported
  by kernel test robot)
- fix return value of evm_xattr_change() (suggested by Christian Brauner)
- simplify EVM_ALLOW_METADATA_WRITES check in evm_write_key() (suggested by
  Mimi)

v4:
- add patch to pass mnt_userns to EVM inode set/remove xattr hooks
  (suggested by Christian Brauner)
- pass mnt_userns to posix_acl_update_mode()
- use IS_ERR_OR_NULL() in evm_xattr_acl_change() (suggested by Mimi)

v3:
- introduce evm_ignore_error_safe() to correctly ignore INTEGRITY_NOLABEL
  and INTEGRITY_NOXATTRS errors
- fix an error in evm_xattr_acl_change()
- replace #ifndef with !IS_ENABLED() in integrity_load_keys()
- reintroduce ima_inode_removexattr()
- adapt patches to apply on top of the idmapped mounts patch set

v2:
- replace EVM_RESET_STATUS flag with evm_status_revalidate()
- introduce IMA post hooks ima_inode_post_setxattr() and
  ima_inode_post_removexattr()
- remove ima_inode_removexattr()
- ignore INTEGRITY_NOLABEL error if the HMAC key is not loaded

v1:
- introduce EVM_RESET_STATUS integrity flag instead of clearing IMA flag
- introduce new template field evmsig
- add description of evm_xattr_acl_change() and evm_xattr_change()

Roberto Sassu (11):
  evm: Execute evm_inode_init_security() only when an HMAC key is loaded
  evm: Load EVM key in ima_load_x509() to avoid appraisal
  evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded
  evm: Introduce evm_status_revalidate()
  evm: Introduce evm_hmac_disabled() to safely ignore verification
    errors
  evm: Allow xattr/attr operations for portable signatures
  evm: Pass user namespace to set/remove xattr hooks
  evm: Allow setxattr() and setattr() for unmodified metadata
  ima: Allow imasig requirement to be satisfied by EVM portable
    signatures
  ima: Introduce template field evmsig and write to field sig as
    fallback
  ima: Don't remove security.ima if file must not be appraised

Roberto Sassu (11):
  evm: Execute evm_inode_init_security() only when an HMAC key is loaded
  evm: Load EVM key in ima_load_x509() to avoid appraisal
  evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded
  evm: Introduce evm_status_revalidate()
  evm: Introduce evm_hmac_disabled() to safely ignore verification
    errors
  evm: Allow xattr/attr operations for portable signatures
  evm: Pass user namespace to set/remove xattr hooks
  evm: Allow setxattr() and setattr() for unmodified metadata
  ima: Allow imasig requirement to be satisfied by EVM portable
    signatures
  ima: Introduce template field evmsig and write to field sig as
    fallback
  ima: Don't remove security.ima if file must not be appraised

 Documentation/ABI/testing/evm             |   5 +-
 Documentation/security/IMA-templates.rst  |   4 +-
 include/linux/evm.h                       |  18 +-
 include/linux/integrity.h                 |   1 +
 security/integrity/evm/evm_main.c         | 227 ++++++++++++++++++++--
 security/integrity/evm/evm_secfs.c        |   5 +-
 security/integrity/iint.c                 |   4 +-
 security/integrity/ima/ima_appraise.c     |  43 ++--
 security/integrity/ima/ima_init.c         |   4 +
 security/integrity/ima/ima_template.c     |   2 +
 security/integrity/ima/ima_template_lib.c |  33 +++-
 security/integrity/ima/ima_template_lib.h |   2 +
 security/security.c                       |   4 +-
 13 files changed, 304 insertions(+), 48 deletions(-)

-- 
2.25.1

The public builtin keys do not need to be appraised by IMA as the
restriction on the IMA/EVM trusted keyrings ensures that a key can be
loaded only if it is signed with a key on the builtin or secondary
keyrings.

However, when evm_load_x509() is called, appraisal is already enabled and
a valid IMA signature must be added to the EVM key to pass verification.

Since the restriction is applied on both IMA and EVM trusted keyrings, it
is safe to disable appraisal also when the EVM key is loaded. This patch
calls evm_load_x509() inside ima_load_x509() if CONFIG_IMA_LOAD_X509 is
enabled, which crosses the normal IMA and EVM boundary.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/iint.c         | 4 +++-
 security/integrity/ima/ima_init.c | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index fca8a9409e4a..8638976f7990 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c

@@ -208,7 +208,9 @@ int integrity_kernel_read(struct file *file, loff_t offset,
 void __init integrity_load_keys(void)
 {
 	ima_load_x509();
-	evm_load_x509();
+
+	if (!IS_ENABLED(CONFIG_IMA_LOAD_X509))
+		evm_load_x509();
 }
 
 static int __init integrity_fs_init(void)

diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index 6e8742916d1d..5076a7d9d23e 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c

@@ -108,6 +108,10 @@ void __init ima_load_x509(void)
 
 	ima_policy_flag &= ~unset_flags;
 	integrity_load_x509(INTEGRITY_KEYRING_IMA, CONFIG_IMA_X509_PATH);
+
+	/* load also EVM key to avoid appraisal */
+	evm_load_x509();
+
 	ima_policy_flag |= unset_flags;
 }
 #endif

-- 
2.25.1

evm_inode_init_security() requires an HMAC key to calculate the HMAC on
initial xattrs provided by LSMs. However, it checks generically whether a
key has been loaded, including also public keys, which is not correct as
public keys are not suitable to calculate the HMAC.

Originally, support for signature verification was introduced to verify a
possibly immutable initial ram disk, when no new files are created, and to
switch to HMAC for the root filesystem. By that time, an HMAC key should
have been loaded and usable to calculate HMACs for new files.

More recently support for requiring an HMAC key was removed from the
kernel, so that signature verification can be used alone. Since this is a
legitimate use case, evm_inode_init_security() should not return an error
when no HMAC key has been loaded.

This patch fixes this problem by replacing the evm_key_loaded() check with
a check of the EVM_INIT_HMAC flag in evm_initialized.

Cc: stable@vger.kernel.org # 4.5.x
Fixes: 26ddabfe96b ("evm: enable EVM when X509 certificate is loaded")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/evm/evm_main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 0de367aaa2d3..7ac5204c8d1f 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -521,7 +521,7 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 }
 
 /*
- * evm_inode_init_security - initializes security.evm
+ * evm_inode_init_security - initializes security.evm HMAC value
  */
 int evm_inode_init_security(struct inode *inode,
 				 const struct xattr *lsm_xattr,

@@ -530,7 +530,8 @@ int evm_inode_init_security(struct inode *inode,
 	struct evm_xattr *xattr_data;
 	int rc;
 
-	if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
+	if (!(evm_initialized & EVM_INIT_HMAC) ||
+	    !evm_protected_xattr(lsm_xattr->name))
 		return 0;
 
 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);

-- 
2.25.1

EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be set to
temporarily disable metadata verification until all xattrs/attrs necessary
to verify an EVM portable signature are copied to the file. This flag is
cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is
calculated on unverified xattrs/attrs.

Currently EVM unnecessarily denies setting this flag if EVM is initialized
with a public key, which is not a concern as it cannot be used to trust
xattrs/attrs updates. This patch removes this limitation.

Cc: stable@vger.kernel.org # 4.16.x
Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 Documentation/ABI/testing/evm      | 5 +++--
 security/integrity/evm/evm_secfs.c | 5 ++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm
index 3c477ba48a31..eb6d70fd6fa2 100644
--- a/Documentation/ABI/testing/evm
+++ b/Documentation/ABI/testing/evm

@@ -49,8 +49,9 @@ Description:
 		modification of EVM-protected metadata and
 		disable all further modification of policy
 
-		Note that once a key has been loaded, it will no longer be
-		possible to enable metadata modification.
+		Note that once an HMAC key has been loaded, it will no longer
+		be possible to enable metadata modification and, if it is
+		already enabled, it will be disabled.
 
 		Until key loading has been signaled EVM can not create
 		or validate the 'security.evm' xattr, but returns

diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index bbc85637e18b..860c48b9a0c3 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c

@@ -81,11 +81,10 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
 		return -EINVAL;
 
 	/* Don't allow a request to freshly enable metadata writes if
-	 * keys are loaded.
+	 * an HMAC key is loaded.
 	 */
 	if ((i & EVM_ALLOW_METADATA_WRITES) &&
-	    ((evm_initialized & EVM_KEY_MASK) != 0) &&
-	    !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
+	    (evm_initialized & EVM_INIT_HMAC) != 0)
 		return -EPERM;
 
 	if (i & EVM_INIT_HMAC) {

-- 
2.25.1

When EVM_ALLOW_METADATA_WRITES is set, EVM allows any operation on
metadata. Its main purpose is to allow users to freely set metadata when it
is protected by a portable signature, until an HMAC key is loaded.

However, callers of evm_verifyxattr() are not notified about metadata
changes and continue to rely on the last status returned by the function.
For example IMA, since it caches the appraisal result, will not call again
evm_verifyxattr() until the appraisal flags are cleared, and will grant
access to the file even if there was a metadata operation that made the
portable signature invalid.

This patch introduces evm_status_revalidate(), which callers of
evm_verifyxattr() can use in their xattr hooks to determine whether
re-validation is necessary and to do the proper actions. IMA calls it in
its xattr hooks to reset the appraisal flags, so that the EVM status is
re-evaluated after a metadata operation.

Lastly, this patch also adds a call to evm_reset_status() in
evm_inode_post_setattr() to invalidate the cached EVM status after a
setattr operation.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/evm.h                   |  6 +++++
 security/integrity/evm/evm_main.c     | 33 +++++++++++++++++++++++----
 security/integrity/ima/ima_appraise.c | 15 ++++++++----
 3 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 8302bc29bb35..e5b7bcb152b9 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h

@@ -35,6 +35,7 @@ extern void evm_inode_post_removexattr(struct dentry *dentry,
 extern int evm_inode_init_security(struct inode *inode,
 				   const struct xattr *xattr_array,
 				   struct xattr *evm);
+extern bool evm_status_revalidate(const char *xattr_name);
 #ifdef CONFIG_FS_POSIX_ACL
 extern int posix_xattr_acl(const char *xattrname);
 #else

@@ -104,5 +105,10 @@ static inline int evm_inode_init_security(struct inode *inode,
 	return 0;
 }
 
+static inline bool evm_status_revalidate(const char *xattr_name)
+{
+	return false;
+}
+
 #endif /* CONFIG_EVM */
 #endif /* LINUX_EVM_H */

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 7ac5204c8d1f..998818283fda 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -425,6 +425,30 @@ static void evm_reset_status(struct inode *inode)
 		iint->evm_status = INTEGRITY_UNKNOWN;
 }
 
+/**
+ * evm_status_revalidate - report whether EVM status re-validation is necessary
+ * @xattr_name: pointer to the affected extended attribute name
+ *
+ * Report whether callers of evm_verifyxattr() should re-validate the
+ * EVM status.
+ *
+ * Return true if re-validation is necessary, false otherwise.
+ */
+bool evm_status_revalidate(const char *xattr_name)
+{
+	if (!evm_key_loaded())
+		return false;
+
+	/* evm_inode_post_setattr() passes NULL */
+	if (!xattr_name)
+		return true;
+
+	if (!evm_protected_xattr(xattr_name) && !posix_xattr_acl(xattr_name))
+		return false;
+
+	return true;
+}
+
 /**
  * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
  * @dentry: pointer to the affected dentry

@@ -441,8 +465,7 @@ static void evm_reset_status(struct inode *inode)
 void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 			     const void *xattr_value, size_t xattr_value_len)
 {
-	if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
-				  && !posix_xattr_acl(xattr_name)))
+	if (!evm_status_revalidate(xattr_name))
 		return;
 
 	evm_reset_status(dentry->d_inode);

@@ -462,7 +485,7 @@ void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
  */
 void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 {
-	if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
+	if (!evm_status_revalidate(xattr_name))
 		return;
 
 	evm_reset_status(dentry->d_inode);

@@ -513,9 +536,11 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
  */
 void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 {
-	if (!evm_key_loaded())
+	if (!evm_status_revalidate(NULL))
 		return;
 
+	evm_reset_status(dentry->d_inode);
+
 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 		evm_update_evmxattr(dentry, NULL, NULL, 0);
 }

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 4e5eb0236278..ddac9e727d3a 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -570,6 +570,7 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 		       const void *xattr_value, size_t xattr_value_len)
 {
 	const struct evm_ima_xattr_data *xvalue = xattr_value;
+	int digsig = 0;
 	int result;
 
 	result = ima_protect_xattr(dentry, xattr_name, xattr_value,

@@ -577,9 +578,12 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 	if (result == 1) {
 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 			return -EINVAL;
-		ima_reset_appraise_flags(d_backing_inode(dentry),
-			xvalue->type == EVM_IMA_XATTR_DIGSIG);
-		result = 0;
+		digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
+	}
+	if (result == 1 || evm_status_revalidate(xattr_name)) {
+		ima_reset_appraise_flags(d_backing_inode(dentry), digsig);
+		if (result == 1)
+			result = 0;
 	}
 	return result;
 }

@@ -589,9 +593,10 @@ int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 	int result;
 
 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
-	if (result == 1) {
+	if (result == 1 || evm_status_revalidate(xattr_name)) {
 		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
-		result = 0;
+		if (result == 1)
+			result = 0;
 	}
 	return result;
 }

-- 
2.25.1

When a file is being created, LSMs can set the initial label with the
inode_init_security hook. If no HMAC key is loaded, the new file will have
LSM xattrs but not the HMAC. It is also possible that the file remains
without protected xattrs after creation if no active LSM provided it.

Unfortunately, EVM will deny any further metadata operation on new files,
as evm_protect_xattr() will always return the INTEGRITY_NOLABEL error, or
INTEGRITY_NOXATTRS if no protected xattrs exist. This would limit the
usability of EVM when only a public key is loaded, as commands such as cp
or tar with the option to preserve xattrs won't work.

This patch introduces the evm_hmac_disabled() function to determine whether
or not it is safe to ignore verification errors, based on the ability of
EVM to calculate HMACs. If the HMAC key is not loaded, and it cannot be
loaded in the future due to the EVM_SETUP_COMPLETE initialization flag,
allowing an operation despite the attrs/xattrs being found invalid will not
make them valid.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/evm/evm_main.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 998818283fda..f625196eee8e 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -90,6 +90,24 @@ static bool evm_key_loaded(void)
 	return (bool)(evm_initialized & EVM_KEY_MASK);
 }
 
+/*
+ * This function determines whether or not it is safe to ignore verification
+ * errors, based on the ability of EVM to calculate HMACs. If the HMAC key
+ * is not loaded, and it cannot be loaded in the future due to the
+ * EVM_SETUP_COMPLETE initialization flag, allowing an operation despite the
+ * attrs/xattrs being found invalid will not make them valid.
+ */
+static bool evm_hmac_disabled(void)
+{
+	if (evm_initialized & EVM_INIT_HMAC)
+		return false;
+
+	if (!(evm_initialized & EVM_SETUP_COMPLETE))
+		return false;
+
+	return true;
+}
+
 static int evm_find_protected_xattrs(struct dentry *dentry)
 {
 	struct inode *inode = d_backing_inode(dentry);

@@ -338,6 +356,10 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 	if (evm_status == INTEGRITY_NOXATTRS) {
 		struct integrity_iint_cache *iint;
 
+		/* Exception if the HMAC is not going to be calculated. */
+		if (evm_hmac_disabled())
+			return 0;
+
 		iint = integrity_iint_find(d_backing_inode(dentry));
 		if (iint && (iint->flags & IMA_NEW_FILE))
 			return 0;

@@ -354,6 +376,9 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 				    -EPERM, 0);
 	}
 out:
+	/* Exception if the HMAC is not going to be calculated. */
+	if (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL)
+		return 0;
 	if (evm_status != INTEGRITY_PASS)
 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 				    dentry->d_name.name, "appraise_metadata",

@@ -515,7 +540,8 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 		return 0;
 	evm_status = evm_verify_current_integrity(dentry);
 	if ((evm_status == INTEGRITY_PASS) ||
-	    (evm_status == INTEGRITY_NOXATTRS))
+	    (evm_status == INTEGRITY_NOXATTRS) ||
+	    (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL))
 		return 0;
 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 			    dentry->d_name.name, "appraise_metadata",

-- 
2.25.1

If files with portable signatures are copied from one location to another
or are extracted from an archive, verification can temporarily fail until
all xattrs/attrs are set in the destination. Only portable signatures may
be moved or copied from one file to another, as they don't depend on
system-specific information such as the inode generation. Instead portable
signatures must include security.ima.

Unlike other security.evm types, EVM portable signatures are also
immutable. Thus, it wouldn't be a problem to allow xattr/attr operations
when verification fails, as portable signatures will never be replaced with
the HMAC on possibly corrupted xattrs/attrs.

This patch first introduces a new integrity status called
INTEGRITY_FAIL_IMMUTABLE, that allows callers of
evm_verify_current_integrity() to detect that a portable signature didn't
pass verification and then adds an exception in evm_protect_xattr() and
evm_inode_setattr() for this status and returns 0 instead of -EPERM.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 include/linux/integrity.h             |  1 +
 security/integrity/evm/evm_main.c     | 33 ++++++++++++++++++++++-----
 security/integrity/ima/ima_appraise.c |  2 ++
 3 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/include/linux/integrity.h b/include/linux/integrity.h
index 2271939c5c31..2ea0f2f65ab6 100644
--- a/include/linux/integrity.h
+++ b/include/linux/integrity.h

@@ -13,6 +13,7 @@ enum integrity_status {
 	INTEGRITY_PASS = 0,
 	INTEGRITY_PASS_IMMUTABLE,
 	INTEGRITY_FAIL,
+	INTEGRITY_FAIL_IMMUTABLE,
 	INTEGRITY_NOLABEL,
 	INTEGRITY_NOXATTRS,
 	INTEGRITY_UNKNOWN,

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index f625196eee8e..9faebff029e6 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -27,7 +27,8 @@
 int evm_initialized;
 
 static const char * const integrity_status_msg[] = {
-	"pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
+	"pass", "pass_immutable", "fail", "fail_immutable", "no_label",
+	"no_xattrs", "unknown"
 };
 int evm_hmac_attrs;
 

@@ -155,7 +156,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 	enum integrity_status evm_status = INTEGRITY_PASS;
 	struct evm_digest digest;
 	struct inode *inode;
-	int rc, xattr_len;
+	int rc, xattr_len, evm_immutable = 0;
 
 	if (iint && (iint->evm_status == INTEGRITY_PASS ||
 		     iint->evm_status == INTEGRITY_PASS_IMMUTABLE))

@@ -200,8 +201,10 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 		if (rc)
 			rc = -EINVAL;
 		break;
-	case EVM_IMA_XATTR_DIGSIG:
 	case EVM_XATTR_PORTABLE_DIGSIG:
+		evm_immutable = 1;
+		fallthrough;
+	case EVM_IMA_XATTR_DIGSIG:
 		/* accept xattr with non-empty signature field */
 		if (xattr_len <= sizeof(struct signature_v2_hdr)) {
 			evm_status = INTEGRITY_FAIL;

@@ -238,9 +241,14 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 		break;
 	}
 
-	if (rc)
-		evm_status = (rc == -ENODATA) ?
-				INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
+	if (rc) {
+		if (rc == -ENODATA)
+			evm_status = INTEGRITY_NOXATTRS;
+		else if (evm_immutable)
+			evm_status = INTEGRITY_FAIL_IMMUTABLE;
+		else
+			evm_status = INTEGRITY_FAIL;
+	}
 out:
 	if (iint)
 		iint->evm_status = evm_status;

@@ -379,6 +387,14 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 	/* Exception if the HMAC is not going to be calculated. */
 	if (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL)
 		return 0;
+
+	/*
+	 * Writing other xattrs is safe for portable signatures, as portable
+	 * signatures are immutable and can never be updated.
+	 */
+	if (evm_status == INTEGRITY_FAIL_IMMUTABLE)
+		return 0;
+
 	if (evm_status != INTEGRITY_PASS)
 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 				    dentry->d_name.name, "appraise_metadata",

@@ -539,8 +555,13 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 	if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
 		return 0;
 	evm_status = evm_verify_current_integrity(dentry);
+	/*
+	 * Writing attrs is safe for portable signatures, as portable signatures
+	 * are immutable and can never be updated.
+	 */
 	if ((evm_status == INTEGRITY_PASS) ||
 	    (evm_status == INTEGRITY_NOXATTRS) ||
+	    (evm_status == INTEGRITY_FAIL_IMMUTABLE) ||
 	    (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL))
 		return 0;
 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index ddac9e727d3a..6d0983a97711 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -416,6 +416,8 @@ int ima_appraise_measurement(enum ima_hooks func,
 	case INTEGRITY_NOLABEL:		/* No security.evm xattr. */
 		cause = "missing-HMAC";
 		goto out;
+	case INTEGRITY_FAIL_IMMUTABLE:
+		fallthrough;
 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
 		cause = "invalid-HMAC";
 		goto out;

-- 
2.25.1

In preparation for 'evm: Allow setxattr() and setattr() for unmodified
metadata', this patch passes mnt_userns to the inode set/remove xattr hooks
so that the GID of the inode on an idmapped mount is correctly determined
by posix_acl_update_mode().

Cc: Christian Brauner <redacted>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Christian Brauner <redacted>
---
 include/linux/evm.h               | 12 ++++++++----
 security/integrity/evm/evm_main.c | 17 +++++++++++------
 security/security.c               |  4 ++--
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index e5b7bcb152b9..8cad46bcec9d 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h

@@ -23,13 +23,15 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
 					     struct integrity_iint_cache *iint);
 extern int evm_inode_setattr(struct dentry *dentry, struct iattr *attr);
 extern void evm_inode_post_setattr(struct dentry *dentry, int ia_valid);
-extern int evm_inode_setxattr(struct dentry *dentry, const char *name,
+extern int evm_inode_setxattr(struct user_namespace *mnt_userns,
+			      struct dentry *dentry, const char *name,
 			      const void *value, size_t size);
 extern void evm_inode_post_setxattr(struct dentry *dentry,
 				    const char *xattr_name,
 				    const void *xattr_value,
 				    size_t xattr_value_len);
-extern int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name);
+extern int evm_inode_removexattr(struct user_namespace *mnt_userns,
+				 struct dentry *dentry, const char *xattr_name);
 extern void evm_inode_post_removexattr(struct dentry *dentry,
 				       const char *xattr_name);
 extern int evm_inode_init_security(struct inode *inode,

@@ -72,7 +74,8 @@ static inline void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 	return;
 }
 
-static inline int evm_inode_setxattr(struct dentry *dentry, const char *name,
+static inline int evm_inode_setxattr(struct user_namespace *mnt_userns,
+				     struct dentry *dentry, const char *name,
 				     const void *value, size_t size)
 {
 	return 0;

@@ -86,7 +89,8 @@ static inline void evm_inode_post_setxattr(struct dentry *dentry,
 	return;
 }
 
-static inline int evm_inode_removexattr(struct dentry *dentry,
+static inline int evm_inode_removexattr(struct user_namespace *mnt_userns,
+					struct dentry *dentry,
 					const char *xattr_name)
 {
 	return 0;

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 9faebff029e6..3745c08c09e6 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -342,7 +342,8 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
  * For posix xattr acls only, permit security.evm, even if it currently
  * doesn't exist, to be updated unless the EVM signature is immutable.
  */
-static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
+static int evm_protect_xattr(struct user_namespace *mnt_userns,
+			     struct dentry *dentry, const char *xattr_name,
 			     const void *xattr_value, size_t xattr_value_len)
 {
 	enum integrity_status evm_status;

@@ -405,6 +406,7 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 
 /**
  * evm_inode_setxattr - protect the EVM extended attribute
+ * @mnt_userns: user namespace of the idmapped mount
  * @dentry: pointer to the affected dentry
  * @xattr_name: pointer to the affected extended attribute name
  * @xattr_value: pointer to the new extended attribute value

@@ -416,8 +418,9 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
  * userspace from writing HMAC value.  Writing 'security.evm' requires
  * requires CAP_SYS_ADMIN privileges.
  */
-int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
-		       const void *xattr_value, size_t xattr_value_len)
+int evm_inode_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
+		       const char *xattr_name, const void *xattr_value,
+		       size_t xattr_value_len)
 {
 	const struct evm_ima_xattr_data *xattr_data = xattr_value;
 

@@ -434,19 +437,21 @@ int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 		    xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
 			return -EPERM;
 	}
-	return evm_protect_xattr(dentry, xattr_name, xattr_value,
+	return evm_protect_xattr(mnt_userns, dentry, xattr_name, xattr_value,
 				 xattr_value_len);
 }
 
 /**
  * evm_inode_removexattr - protect the EVM extended attribute
+ * @mnt_userns: user namespace of the idmapped mount
  * @dentry: pointer to the affected dentry
  * @xattr_name: pointer to the affected extended attribute name
  *
  * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
  * the current value is valid.
  */
-int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
+int evm_inode_removexattr(struct user_namespace *mnt_userns,
+			  struct dentry *dentry, const char *xattr_name)
 {
 	/* Policy permits modification of the protected xattrs even though
 	 * there's no HMAC key loaded

@@ -454,7 +459,7 @@ int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
 	if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
 		return 0;
 
-	return evm_protect_xattr(dentry, xattr_name, NULL, 0);
+	return evm_protect_xattr(mnt_userns, dentry, xattr_name, NULL, 0);
 }
 
 static void evm_reset_status(struct inode *inode)

diff --git a/security/security.c b/security/security.c
index b38155b2de83..e9f8010a2341 100644
--- a/security/security.c
+++ b/security/security.c

@@ -1354,7 +1354,7 @@ int security_inode_setxattr(struct user_namespace *mnt_userns,
 	ret = ima_inode_setxattr(dentry, name, value, size);
 	if (ret)
 		return ret;
-	return evm_inode_setxattr(dentry, name, value, size);
+	return evm_inode_setxattr(mnt_userns, dentry, name, value, size);
 }
 
 void security_inode_post_setxattr(struct dentry *dentry, const char *name,

@@ -1399,7 +1399,7 @@ int security_inode_removexattr(struct user_namespace *mnt_userns,
 	ret = ima_inode_removexattr(dentry, name);
 	if (ret)
 		return ret;
-	return evm_inode_removexattr(dentry, name);
+	return evm_inode_removexattr(mnt_userns, dentry, name);
 }
 
 int security_inode_need_killpriv(struct dentry *dentry)

-- 
2.25.1

With the patch to allow xattr/attr operations if a portable signature
verification fails, cp and tar can copy all xattrs/attrs so that at the
end of the process verification succeeds.

However, it might happen that the xattrs/attrs are already set to the
correct value (taken at signing time) and signature verification succeeds
before the copy has completed. For example, an archive might contains files
owned by root and the archive is extracted by root.

Then, since portable signatures are immutable, all subsequent operations
fail (e.g. fchown()), even if the operation is legitimate (does not alter
the current value).

This patch avoids this problem by reporting successful operation to user
space when that operation does not alter the current value of xattrs/attrs.

Cc: Christian Brauner <redacted>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Reported-by: kernel test robot <redacted>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Christian Brauner <redacted>
---
 security/integrity/evm/evm_main.c | 111 +++++++++++++++++++++++++++++-
 1 file changed, 110 insertions(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 3745c08c09e6..793e6556b004 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -18,6 +18,7 @@
 #include <linux/integrity.h>
 #include <linux/evm.h>
 #include <linux/magic.h>
+#include <linux/posix_acl_xattr.h>
 
 #include <crypto/hash.h>
 #include <crypto/hash_info.h>

@@ -330,6 +331,90 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 }
 
+/*
+ * evm_xattr_acl_change - check if passed ACL changes the inode mode
+ * @mnt_userns: user namespace of the idmapped mount
+ * @dentry: pointer to the affected dentry
+ * @xattr_name: requested xattr
+ * @xattr_value: requested xattr value
+ * @xattr_value_len: requested xattr value length
+ *
+ * Check if passed ACL changes the inode mode, which is protected by EVM.
+ *
+ * Returns 1 if passed ACL causes inode mode change, 0 otherwise.
+ */
+static int evm_xattr_acl_change(struct user_namespace *mnt_userns,
+				struct dentry *dentry, const char *xattr_name,
+				const void *xattr_value, size_t xattr_value_len)
+{
+#ifdef CONFIG_FS_POSIX_ACL
+	umode_t mode;
+	struct posix_acl *acl = NULL, *acl_res;
+	struct inode *inode = d_backing_inode(dentry);
+	int rc;
+
+	/* user_ns is not relevant here, ACL_USER/ACL_GROUP don't have impact
+	 * on the inode mode (see posix_acl_equiv_mode()).
+	 */
+	acl = posix_acl_from_xattr(&init_user_ns, xattr_value, xattr_value_len);
+	if (IS_ERR_OR_NULL(acl))
+		return 1;
+
+	acl_res = acl;
+	/* Passing mnt_userns is necessary to correctly determine the GID in
+	 * an idmapped mount, as the GID is used to clear the setgid bit in
+	 * the inode mode.
+	 */
+	rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res);
+
+	posix_acl_release(acl);
+
+	if (rc)
+		return 1;
+
+	if (inode->i_mode != mode)
+		return 1;
+#endif
+	return 0;
+}
+
+/*
+ * evm_xattr_change - check if passed xattr value differs from current value
+ * @mnt_userns: user namespace of the idmapped mount
+ * @dentry: pointer to the affected dentry
+ * @xattr_name: requested xattr
+ * @xattr_value: requested xattr value
+ * @xattr_value_len: requested xattr value length
+ *
+ * Check if passed xattr value differs from current value.
+ *
+ * Returns 1 if passed xattr value differs from current value, 0 otherwise.
+ */
+static int evm_xattr_change(struct user_namespace *mnt_userns,
+			    struct dentry *dentry, const char *xattr_name,
+			    const void *xattr_value, size_t xattr_value_len)
+{
+	char *xattr_data = NULL;
+	int rc = 0;
+
+	if (posix_xattr_acl(xattr_name))
+		return evm_xattr_acl_change(mnt_userns, dentry, xattr_name,
+					    xattr_value, xattr_value_len);
+
+	rc = vfs_getxattr_alloc(&init_user_ns, dentry, xattr_name, &xattr_data,
+				0, GFP_NOFS);
+	if (rc < 0)
+		return 1;
+
+	if (rc == xattr_value_len)
+		rc = !!memcmp(xattr_value, xattr_data, rc);
+	else
+		rc = 1;
+
+	kfree(xattr_data);
+	return rc;
+}
+
 /*
  * evm_protect_xattr - protect the EVM extended attribute
  *

@@ -396,7 +481,13 @@ static int evm_protect_xattr(struct user_namespace *mnt_userns,
 	if (evm_status == INTEGRITY_FAIL_IMMUTABLE)
 		return 0;
 
-	if (evm_status != INTEGRITY_PASS)
+	if (evm_status == INTEGRITY_PASS_IMMUTABLE &&
+	    !evm_xattr_change(mnt_userns, dentry, xattr_name, xattr_value,
+			      xattr_value_len))
+		return 0;
+
+	if (evm_status != INTEGRITY_PASS &&
+	    evm_status != INTEGRITY_PASS_IMMUTABLE)
 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 				    dentry->d_name.name, "appraise_metadata",
 				    integrity_status_msg[evm_status],

@@ -539,6 +630,19 @@ void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 }
 
+static int evm_attr_change(struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = d_backing_inode(dentry);
+	unsigned int ia_valid = attr->ia_valid;
+
+	if ((!(ia_valid & ATTR_UID) || uid_eq(attr->ia_uid, inode->i_uid)) &&
+	    (!(ia_valid & ATTR_GID) || gid_eq(attr->ia_gid, inode->i_gid)) &&
+	    (!(ia_valid & ATTR_MODE) || attr->ia_mode == inode->i_mode))
+		return 0;
+
+	return 1;
+}
+
 /**
  * evm_inode_setattr - prevent updating an invalid EVM extended attribute
  * @dentry: pointer to the affected dentry

@@ -569,6 +673,11 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 	    (evm_status == INTEGRITY_FAIL_IMMUTABLE) ||
 	    (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL))
 		return 0;
+
+	if (evm_status == INTEGRITY_PASS_IMMUTABLE &&
+	    !evm_attr_change(dentry, attr))
+		return 0;
+
 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 			    dentry->d_name.name, "appraise_metadata",
 			    integrity_status_msg[evm_status], -EPERM, 0);

-- 
2.25.1

System administrators can require that all accessed files have a signature
by specifying appraise_type=imasig in a policy rule.

Currently, IMA signatures satisfy this requirement. Appended signatures may
also satisfy this requirement, but are not applicable as IMA signatures.
IMA/appended signatures ensure data source authentication for file content
and prevent any change. EVM signatures instead ensure data source
authentication for file metadata. Given that the digest or signature of the
file content must be included in the metadata, EVM signatures provide the
same file data guarantees of IMA signatures, as well as providing file
metadata guarantees.

This patch lets systems protected with EVM signatures pass appraisal
verification if the appraise_type=imasig requirement is specified in the
policy. This facilitates deployment in the scenarios where only EVM
signatures are available.

The patch makes the following changes:

file xattr types:
security.ima: IMA_XATTR_DIGEST/IMA_XATTR_DIGEST_NG
security.evm: EVM_XATTR_PORTABLE_DIGSIG

execve(), mmap(), open() behavior (with appraise_type=imasig):
before: denied (file without IMA signature, imasig requirement not met)
after: allowed (file with EVM portable signature, imasig requirement met)

open(O_WRONLY) behavior (without appraise_type=imasig):
before: allowed (file without IMA signature, not immutable)
after: denied (file with EVM portable signature, immutable)

In addition, similarly to IMA signatures, this patch temporarily allows
new files without or with incomplete metadata to be opened so that content
can be written.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/ima/ima_appraise.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 6d0983a97711..23af45d8ac58 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -242,12 +242,16 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
 		hash_start = 1;
 		fallthrough;
 	case IMA_XATTR_DIGEST:
-		if (iint->flags & IMA_DIGSIG_REQUIRED) {
-			*cause = "IMA-signature-required";
-			*status = INTEGRITY_FAIL;
-			break;
+		if (*status != INTEGRITY_PASS_IMMUTABLE) {
+			if (iint->flags & IMA_DIGSIG_REQUIRED) {
+				*cause = "IMA-signature-required";
+				*status = INTEGRITY_FAIL;
+				break;
+			}
+			clear_bit(IMA_DIGSIG, &iint->atomic_flags);
+		} else {
+			set_bit(IMA_DIGSIG, &iint->atomic_flags);
 		}
-		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 				iint->ima_hash->length)
 			/*

@@ -417,6 +421,7 @@ int ima_appraise_measurement(enum ima_hooks func,
 		cause = "missing-HMAC";
 		goto out;
 	case INTEGRITY_FAIL_IMMUTABLE:
+		set_bit(IMA_DIGSIG, &iint->atomic_flags);
 		fallthrough;
 	case INTEGRITY_FAIL:		/* Invalid HMAC/signature. */
 		cause = "invalid-HMAC";

@@ -461,9 +466,12 @@ int ima_appraise_measurement(enum ima_hooks func,
 				status = INTEGRITY_PASS;
 		}
 
-		/* Permit new files with file signatures, but without data. */
+		/*
+		 * Permit new files with file/EVM portable signatures, but
+		 * without data.
+		 */
 		if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
-		    xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
+		    test_bit(IMA_DIGSIG, &iint->atomic_flags)) {
 			status = INTEGRITY_PASS;
 		}
 

@@ -581,6 +589,8 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
 		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
 			return -EINVAL;
 		digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG);
+	} else if (!strcmp(xattr_name, XATTR_NAME_EVM) && xattr_value_len > 0) {
+		digsig = (xvalue->type == EVM_XATTR_PORTABLE_DIGSIG);
 	}
 	if (result == 1 || evm_status_revalidate(xattr_name)) {
 		ima_reset_appraise_flags(d_backing_inode(dentry), digsig);

-- 
2.25.1

With the patch to accept EVM portable signatures when the
appraise_type=imasig requirement is specified in the policy, appraisal can
be successfully done even if the file does not have an IMA signature.

However, remote attestation would not see that a different signature type
was used, as only IMA signatures can be included in the measurement list.
This patch solves the issue by introducing the new template field 'evmsig'
to show EVM portable signatures and by including its value in the existing
field 'sig' if the IMA signature is not found.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
---
 Documentation/security/IMA-templates.rst  |  4 ++-
 security/integrity/ima/ima_template.c     |  2 ++
 security/integrity/ima/ima_template_lib.c | 33 ++++++++++++++++++++++-
 security/integrity/ima/ima_template_lib.h |  2 ++
 4 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index c5a8432972ef..9f3e86ab028a 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst

@@ -70,9 +70,11 @@ descriptors by adding their identifier to the format string
    prefix is shown only if the hash algorithm is not SHA1 or MD5);
  - 'd-modsig': the digest of the event without the appended modsig;
  - 'n-ng': the name of the event, without size limitations;
- - 'sig': the file signature;
+ - 'sig': the file signature, or the EVM portable signature if the file
+   signature is not found;
  - 'modsig' the appended file signature;
  - 'buf': the buffer data that was used to generate the hash without size limitations;
+ - 'evmsig': the EVM portable signature;
 
 
 Below, there is the list of defined template descriptors:

diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index 4e081e650047..7a60848c04a5 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c

@@ -45,6 +45,8 @@ static const struct ima_template_field supported_fields[] = {
 	 .field_show = ima_show_template_digest_ng},
 	{.field_id = "modsig", .field_init = ima_eventmodsig_init,
 	 .field_show = ima_show_template_sig},
+	{.field_id = "evmsig", .field_init = ima_eventevmsig_init,
+	 .field_show = ima_show_template_sig},
 };
 
 /*

diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index c022ee9e2a4e..4314d9a3514c 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c

@@ -10,6 +10,7 @@
  */
 
 #include "ima_template_lib.h"
+#include <linux/xattr.h>
 
 static bool ima_template_hash_algo_allowed(u8 algo)
 {

@@ -438,7 +439,7 @@ int ima_eventsig_init(struct ima_event_data *event_data,
 	struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
 
 	if ((!xattr_value) || (xattr_value->type != EVM_IMA_XATTR_DIGSIG))
-		return 0;
+		return ima_eventevmsig_init(event_data, field_data);
 
 	return ima_write_template_field_data(xattr_value, event_data->xattr_len,
 					     DATA_FMT_HEX, field_data);

@@ -484,3 +485,33 @@ int ima_eventmodsig_init(struct ima_event_data *event_data,
 	return ima_write_template_field_data(data, data_len, DATA_FMT_HEX,
 					     field_data);
 }
+
+/*
+ *  ima_eventevmsig_init - include the EVM portable signature as part of the
+ *  template data
+ */
+int ima_eventevmsig_init(struct ima_event_data *event_data,
+			 struct ima_field_data *field_data)
+{
+	struct evm_ima_xattr_data *xattr_data = NULL;
+	int rc = 0;
+
+	if (!event_data->file)
+		return 0;
+
+	rc = vfs_getxattr_alloc(&init_user_ns, file_dentry(event_data->file),
+				XATTR_NAME_EVM, (char **)&xattr_data, 0,
+				GFP_NOFS);
+	if (rc <= 0)
+		return 0;
+
+	if (xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG) {
+		kfree(xattr_data);
+		return 0;
+	}
+
+	rc = ima_write_template_field_data((char *)xattr_data, rc, DATA_FMT_HEX,
+					   field_data);
+	kfree(xattr_data);
+	return rc;
+}

diff --git a/security/integrity/ima/ima_template_lib.h b/security/integrity/ima/ima_template_lib.h
index 6b3b880637a0..f4b2a2056d1d 100644
--- a/security/integrity/ima/ima_template_lib.h
+++ b/security/integrity/ima/ima_template_lib.h

@@ -46,4 +46,6 @@ int ima_eventbuf_init(struct ima_event_data *event_data,
 		      struct ima_field_data *field_data);
 int ima_eventmodsig_init(struct ima_event_data *event_data,
 			 struct ima_field_data *field_data);
+int ima_eventevmsig_init(struct ima_event_data *event_data,
+			 struct ima_field_data *field_data);
 #endif /* __LINUX_IMA_TEMPLATE_LIB_H */

-- 
2.25.1

Files might come from a remote source and might have xattrs, including
security.ima. It should not be IMA task to decide whether security.ima
should be kept or not. This patch removes the removexattr() system
call in ima_inode_post_setattr().

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/ima/ima_appraise.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 23af45d8ac58..e1bd61f76f9e 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -532,8 +532,6 @@ void ima_inode_post_setattr(struct user_namespace *mnt_userns,
 		return;
 
 	action = ima_must_appraise(mnt_userns, inode, MAY_ACCESS, POST_SETATTR);
-	if (!action)
-		__vfs_removexattr(&init_user_ns, dentry, XATTR_NAME_IMA);
 	iint = integrity_iint_find(inode);
 	if (iint) {
 		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);

-- 
2.25.1

When a file is being created, LSMs can set the initial label with the
inode_init_security hook. If no HMAC key is loaded, the new file will have
LSM xattrs but not the HMAC. It is also possible that the file remains
without protected xattrs after creation if no active LSM provided it.

Unfortunately, EVM will deny any further metadata operation on new files,
as evm_protect_xattr() will always return the INTEGRITY_NOLABEL error, or
INTEGRITY_NOXATTRS if no protected xattrs exist. This would limit the
usability of EVM when only a public key is loaded, as commands such as cp
or tar with the option to preserve xattrs won't work.

This patch introduces the evm_hmac_disabled() function to determine whether
or not it is safe to ignore verification errors, based on the ability of
EVM to calculate HMACs. If the HMAC key is not loaded, and it cannot be
loaded in the future due to the EVM_SETUP_COMPLETE initialization flag,
allowing an operation despite the attrs/xattrs being found invalid will not
make them valid.

Since the post hooks can be executed even when the HMAC key is not loaded,
this patch also ensures that the EVM_INIT_HMAC initialization flag is set
before the post hooks call evm_update_evmxattr().

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/evm/evm_main.c | 37 ++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 998818283fda..940e5f0a5f93 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c

@@ -90,6 +90,24 @@ static bool evm_key_loaded(void)
 	return (bool)(evm_initialized & EVM_KEY_MASK);
 }
 
+/*
+ * This function determines whether or not it is safe to ignore verification
+ * errors, based on the ability of EVM to calculate HMACs. If the HMAC key
+ * is not loaded, and it cannot be loaded in the future due to the
+ * EVM_SETUP_COMPLETE initialization flag, allowing an operation despite the
+ * attrs/xattrs being found invalid will not make them valid.
+ */
+static bool evm_hmac_disabled(void)
+{
+	if (evm_initialized & EVM_INIT_HMAC)
+		return false;
+
+	if (!(evm_initialized & EVM_SETUP_COMPLETE))
+		return false;
+
+	return true;
+}
+
 static int evm_find_protected_xattrs(struct dentry *dentry)
 {
 	struct inode *inode = d_backing_inode(dentry);

@@ -338,6 +356,10 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 	if (evm_status == INTEGRITY_NOXATTRS) {
 		struct integrity_iint_cache *iint;
 
+		/* Exception if the HMAC is not going to be calculated. */
+		if (evm_hmac_disabled())
+			return 0;
+
 		iint = integrity_iint_find(d_backing_inode(dentry));
 		if (iint && (iint->flags & IMA_NEW_FILE))
 			return 0;

@@ -354,6 +376,9 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
 				    -EPERM, 0);
 	}
 out:
+	/* Exception if the HMAC is not going to be calculated. */
+	if (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL)
+		return 0;
 	if (evm_status != INTEGRITY_PASS)
 		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 				    dentry->d_name.name, "appraise_metadata",

@@ -470,6 +495,9 @@ void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 
 	evm_reset_status(dentry->d_inode);
 
+	if (!(evm_initialized & EVM_INIT_HMAC))
+		return;
+
 	evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
 }
 

@@ -490,6 +518,9 @@ void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
 
 	evm_reset_status(dentry->d_inode);
 
+	if (!(evm_initialized & EVM_INIT_HMAC))
+		return;
+
 	evm_update_evmxattr(dentry, xattr_name, NULL, 0);
 }
 

@@ -515,7 +546,8 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
 		return 0;
 	evm_status = evm_verify_current_integrity(dentry);
 	if ((evm_status == INTEGRITY_PASS) ||
-	    (evm_status == INTEGRITY_NOXATTRS))
+	    (evm_status == INTEGRITY_NOXATTRS) ||
+	    (evm_hmac_disabled() && evm_status == INTEGRITY_NOLABEL))
 		return 0;
 	integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
 			    dentry->d_name.name, "appraise_metadata",

@@ -541,6 +573,9 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 
 	evm_reset_status(dentry->d_inode);
 
+	if (!(evm_initialized & EVM_INIT_HMAC))
+		return;
+
 	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 		evm_update_evmxattr(dentry, NULL, NULL, 0);
 }

-- 
2.25.1

On Wed, 2021-05-05 at 13:29 +0200, Roberto Sassu wrote:

EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be set to
temporarily disable metadata verification until all xattrs/attrs necessary
to verify an EVM portable signature are copied to the file. This flag is
cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is
calculated on unverified xattrs/attrs.

Currently EVM unnecessarily denies setting this flag if EVM is initialized
with a public key, which is not a concern as it cannot be used to trust
xattrs/attrs updates. This patch removes this limitation.

Cc: stable@vger.kernel.org # 4.16.x
Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Once the comments below are addressed, 

Reviewed-by:  Mimi Zohar <zohar@linux.ibm.com>

It's worth mentioning that echo'ing a new value is additive.  Once EVM
metadata modification is enabled, the only way of disabling it is by
enabling an HMAC key.  It's also worth mentioning that metadata writes
are only permitted once further changes to the EVM policy are disabled.
Perhaps the best way of explaining this is by including a new example -
echo 6> <securityfs>/evm.

Please drop the word "freshly".  While updating the comment, please
move the sentence starting with "Don't" to a new line.

 	if ((i & EVM_ALLOW_METADATA_WRITES) &&
-	    ((evm_initialized & EVM_KEY_MASK) != 0) &&
-	    !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
+	    (evm_initialized & EVM_INIT_HMAC) != 0)
 		return -EPERM;
 
 	if (i & EVM_INIT_HMAC) {

On Wed, 2021-05-05 at 13:29 +0200, Roberto Sassu wrote:

When EVM_ALLOW_METADATA_WRITES is set, EVM allows any operation on
metadata. Its main purpose is to allow users to freely set metadata when it
is protected by a portable signature, until an HMAC key is loaded.

However, callers of evm_verifyxattr() are not notified about metadata
changes and continue to rely on the last status returned by the function.
For example IMA, since it caches the appraisal result, will not call again
evm_verifyxattr() until the appraisal flags are cleared, and will grant
access to the file even if there was a metadata operation that made the
portable signature invalid.

This patch introduces evm_status_revalidate(), which callers of
evm_verifyxattr() can use in their xattr hooks to determine whether
re-validation is necessary and to do the proper actions. IMA calls it in
its xattr hooks to reset the appraisal flags, so that the EVM status is
re-evaluated after a metadata operation.

Lastly, this patch also adds a call to evm_reset_status() in
evm_inode_post_setattr() to invalidate the cached EVM status after a
setattr operation.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

I'm really  sorry for the patch churn, but could you rename
evm_status_revalidate() to evm_revalidate_status().

Otherwise,

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>

thanks,

Mimi

On Fri, 2021-05-07 at 15:31 +0200, Roberto Sassu wrote:

When a file is being created, LSMs can set the initial label with the
inode_init_security hook. If no HMAC key is loaded, the new file will have
LSM xattrs but not the HMAC. It is also possible that the file remains
without protected xattrs after creation if no active LSM provided it.

Unfortunately, EVM will deny any further metadata operation on new files,
as evm_protect_xattr() will always return the INTEGRITY_NOLABEL error, or
INTEGRITY_NOXATTRS if no protected xattrs exist. This would limit the
usability of EVM when only a public key is loaded, as commands such as cp
or tar with the option to preserve xattrs won't work.

This patch introduces the evm_hmac_disabled() function to determine whether
or not it is safe to ignore verification errors, based on the ability of
EVM to calculate HMACs. If the HMAC key is not loaded, and it cannot be
loaded in the future due to the EVM_SETUP_COMPLETE initialization flag,
allowing an operation despite the attrs/xattrs being found invalid will not
make them valid.

Since the post hooks can be executed even when the HMAC key is not loaded,
this patch also ensures that the EVM_INIT_HMAC initialization flag is set
before the post hooks call evm_update_evmxattr().

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>

Thanks, Robert!

Reviewed-by:  Mimi Zohar <zohar@linux.ibm.com>

Hi Roberto,

On Wed, 2021-05-05 at 13:33 +0200, Roberto Sassu wrote:

With the patch to allow xattr/attr operations if a portable signature
verification fails, cp and tar can copy all xattrs/attrs so that at the
end of the process verification succeeds.

However, it might happen that the xattrs/attrs are already set to the
correct value (taken at signing time) and signature verification succeeds
before the copy has completed. For example, an archive might contains files
owned by root and the archive is extracted by root.

Then, since portable signatures are immutable, all subsequent operations
fail (e.g. fchown()), even if the operation is legitimate (does not alter
the current value).

This patch avoids this problem by reporting successful operation to user
space when that operation does not alter the current value of xattrs/attrs.

I must be missing something.  If both the IMA and EVM status flags are
reset after xattr or attr modification, do we really need to prevent
any metadata - same or different - changes?  Both evm_protect_xattr()
and evm_inode_setattr() would need to be modified to allow
INTEGRITY_PASS_IMMUTABLE.

thanks,

Mimi

From: Mimi Zohar [mailto:zohar@linux.ibm.com]
Sent: Tuesday, May 11, 2021 3:42 PM
On Wed, 2021-05-05 at 13:29 +0200, Roberto Sassu wrote:

quoted

EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be

set to

quoted

temporarily disable metadata verification until all xattrs/attrs necessary
to verify an EVM portable signature are copied to the file. This flag is
cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is
calculated on unverified xattrs/attrs.

Currently EVM unnecessarily denies setting this flag if EVM is initialized
with a public key, which is not a concern as it cannot be used to trust
xattrs/attrs updates. This patch removes this limitation.

Cc: stable@vger.kernel.org # 4.16.x
Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-

protected metadata")

quoted

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Once the comments below are addressed,

Reviewed-by:  Mimi Zohar <zohar@linux.ibm.com>

quoted

---
 Documentation/ABI/testing/evm      | 5 +++--
 security/integrity/evm/evm_secfs.c | 5 ++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/evm

b/Documentation/ABI/testing/evm

quoted

index 3c477ba48a31..eb6d70fd6fa2 100644

--- a/Documentation/ABI/testing/evm
+++ b/Documentation/ABI/testing/evm

@@ -49,8 +49,9 @@ Description:
 		modification of EVM-protected metadata and
 		disable all further modification of policy

-		Note that once a key has been loaded, it will no longer be
-		possible to enable metadata modification.
+		Note that once an HMAC key has been loaded, it will no longer
+		be possible to enable metadata modification and, if it is
+		already enabled, it will be disabled.

It's worth mentioning that echo'ing a new value is additive.  Once EVM
metadata modification is enabled, the only way of disabling it is by
enabling an HMAC key.  It's also worth mentioning that metadata writes
are only permitted once further changes to the EVM policy are disabled.

If I'm not wrong, it is not required to set EVM_SETUP_COMPLETE to allow
metadata writes. I think the original idea was to boot a system in a way
that portable signatures can be written, and then to enable enforcement.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

Perhaps the best way of explaining this is by including a new example -
echo 6> <securityfs>/evm.

quoted

 		Until key loading has been signaled EVM can not create
 		or validate the 'security.evm' xattr, but returns

diff --git a/security/integrity/evm/evm_secfs.c

b/security/integrity/evm/evm_secfs.c

quoted

index bbc85637e18b..860c48b9a0c3 100644

--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c

@@ -81,11 +81,10 @@ static ssize_t evm_write_key(struct file *file, const

char __user *buf,

quoted

 		return -EINVAL;

 	/* Don't allow a request to freshly enable metadata writes if
-	 * keys are loaded.
+	 * an HMAC key is loaded.
 	 */

Please drop the word "freshly".  While updating the comment, please
move the sentence starting with "Don't" to a new line.

quoted

 	if ((i & EVM_ALLOW_METADATA_WRITES) &&
-	    ((evm_initialized & EVM_KEY_MASK) != 0) &&
-	    !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
+	    (evm_initialized & EVM_INIT_HMAC) != 0)
 		return -EPERM;

 	if (i & EVM_INIT_HMAC) {

From: Mimi Zohar [mailto:zohar@linux.ibm.com]
Sent: Tuesday, May 11, 2021 4:12 PM
Hi Roberto,

On Wed, 2021-05-05 at 13:33 +0200, Roberto Sassu wrote:

quoted

With the patch to allow xattr/attr operations if a portable signature
verification fails, cp and tar can copy all xattrs/attrs so that at the
end of the process verification succeeds.

However, it might happen that the xattrs/attrs are already set to the
correct value (taken at signing time) and signature verification succeeds
before the copy has completed. For example, an archive might contains files
owned by root and the archive is extracted by root.

Then, since portable signatures are immutable, all subsequent operations
fail (e.g. fchown()), even if the operation is legitimate (does not alter
the current value).

This patch avoids this problem by reporting successful operation to user
space when that operation does not alter the current value of xattrs/attrs.

I must be missing something.  If both the IMA and EVM status flags are
reset after xattr or attr modification, do we really need to prevent
any metadata - same or different - changes?  Both evm_protect_xattr()
and evm_inode_setattr() would need to be modified to allow
INTEGRITY_PASS_IMMUTABLE.

Hi Mimi

yes, given that the IMA and EVM flags are reset, it should not be
a problem to allow changes. However, I think it is useful to keep
the current behavior. For example, it would prevent an accidental
change of the SELinux label during the relabeling process.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

thanks,

Mimi

On Tue, 2021-05-11 at 14:21 +0000, Roberto Sassu wrote:

quoted

On Wed, 2021-05-05 at 13:33 +0200, Roberto Sassu wrote:

quoted

With the patch to allow xattr/attr operations if a portable signature
verification fails, cp and tar can copy all xattrs/attrs so that at the
end of the process verification succeeds.

However, it might happen that the xattrs/attrs are already set to the
correct value (taken at signing time) and signature verification succeeds
before the copy has completed. For example, an archive might contains files
owned by root and the archive is extracted by root.

Then, since portable signatures are immutable, all subsequent operations
fail (e.g. fchown()), even if the operation is legitimate (does not alter
the current value).

This patch avoids this problem by reporting successful operation to user
space when that operation does not alter the current value of xattrs/attrs.

I must be missing something.  If both the IMA and EVM status flags are
reset after xattr or attr modification, do we really need to prevent
any metadata - same or different - changes?  Both evm_protect_xattr()
and evm_inode_setattr() would need to be modified to allow
INTEGRITY_PASS_IMMUTABLE.

yes, given that the IMA and EVM flags are reset, it should not be
a problem to allow changes. However, I think it is useful to keep
the current behavior. For example, it would prevent an accidental
change of the SELinux label during the relabeling process.

I understand we might want to prevent accidental or malicious changes,
but that isn't the purpose of this patch set.  The patch description
would also need to be updated to reflect the real purpose.

thanks,

Mimi

From: Mimi Zohar [mailto:zohar@linux.ibm.com]
Sent: Tuesday, May 11, 2021 4:41 PM
On Tue, 2021-05-11 at 14:21 +0000, Roberto Sassu wrote:

quoted

quoted

On Wed, 2021-05-05 at 13:33 +0200, Roberto Sassu wrote:

quoted

With the patch to allow xattr/attr operations if a portable signature
verification fails, cp and tar can copy all xattrs/attrs so that at the
end of the process verification succeeds.

However, it might happen that the xattrs/attrs are already set to the
correct value (taken at signing time) and signature verification succeeds
before the copy has completed. For example, an archive might contains

files

quoted

quoted

quoted

owned by root and the archive is extracted by root.

Then, since portable signatures are immutable, all subsequent operations
fail (e.g. fchown()), even if the operation is legitimate (does not alter
the current value).

This patch avoids this problem by reporting successful operation to user
space when that operation does not alter the current value of

xattrs/attrs.

quoted

quoted

I must be missing something.  If both the IMA and EVM status flags are
reset after xattr or attr modification, do we really need to prevent
any metadata - same or different - changes?  Both evm_protect_xattr()
and evm_inode_setattr() would need to be modified to allow
INTEGRITY_PASS_IMMUTABLE.

yes, given that the IMA and EVM flags are reset, it should not be
a problem to allow changes. However, I think it is useful to keep
the current behavior. For example, it would prevent an accidental
change of the SELinux label during the relabeling process.

I understand we might want to prevent accidental or malicious changes,
but that isn't the purpose of this patch set.  The patch description
would also need to be updated to reflect the real purpose.

We would be changing the expectation that metadata changes
are denied, which was defined with the original patches.

I would prefer to keep the current behavior, but if your suggestion
is to allow metadata changes, I will modify the patch set.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

thanks,

Mimi

On Tue, 2021-05-11 at 14:12 +0000, Roberto Sassu wrote:

quoted

From: Mimi Zohar [mailto:zohar@linux.ibm.com]
Sent: Tuesday, May 11, 2021 3:42 PM
On Wed, 2021-05-05 at 13:29 +0200, Roberto Sassu wrote:

quoted

EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be

set to

quoted

temporarily disable metadata verification until all xattrs/attrs necessary
to verify an EVM portable signature are copied to the file. This flag is
cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is
calculated on unverified xattrs/attrs.

Currently EVM unnecessarily denies setting this flag if EVM is initialized
with a public key, which is not a concern as it cannot be used to trust
xattrs/attrs updates. This patch removes this limitation.

Cc: stable@vger.kernel.org # 4.16.x
Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-

protected metadata")

quoted

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Once the comments below are addressed,

Reviewed-by:  Mimi Zohar <zohar@linux.ibm.com>

quoted

---
 Documentation/ABI/testing/evm      | 5 +++--
 security/integrity/evm/evm_secfs.c | 5 ++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/evm

b/Documentation/ABI/testing/evm

quoted

index 3c477ba48a31..eb6d70fd6fa2 100644

--- a/Documentation/ABI/testing/evm
+++ b/Documentation/ABI/testing/evm

@@ -49,8 +49,9 @@ Description:
 		modification of EVM-protected metadata and
 		disable all further modification of policy

-		Note that once a key has been loaded, it will no longer be
-		possible to enable metadata modification.
+		Note that once an HMAC key has been loaded, it will no longer
+		be possible to enable metadata modification and, if it is
+		already enabled, it will be disabled.

It's worth mentioning that echo'ing a new value is additive.  Once EVM
metadata modification is enabled, the only way of disabling it is by
enabling an HMAC key.  It's also worth mentioning that metadata writes
are only permitted once further changes to the EVM policy are disabled.

If I'm not wrong, it is not required to set EVM_SETUP_COMPLETE to allow
metadata writes.

Agreed, EVM_SETUP_COMPLETE is not needed to allow metadata writes. 
Once EVM_ALLOW_METADATA_WRITES is enabled, however, there is no way of
unsetting it without loading the HMAC key.

I think the original idea was to boot a system in a way
that portable signatures can be written, and then to enable enforcement.

Nothing special is needed to write portable signatures.  Based on the
documentation, I think the original intention supports three modes:
- only enable HMAC validation  (1)
- enable both HMAC and digital signature validation (3)
- only enable digital signature validation and allow modification of
EVM-protected metadata (6)

The third example is enabled using "0x80000006", which also prevents
enabling HMAC verification.  Leaving out the example of enabling just
digital signature validation without modification of EVM protected
metadata seems to have been intentional.

thanks,

Mimi

On Tue, 2021-05-11 at 14:54 +0000, Roberto Sassu wrote:

quoted

On Tue, 2021-05-11 at 14:21 +0000, Roberto Sassu wrote:

quoted

quoted

On Wed, 2021-05-05 at 13:33 +0200, Roberto Sassu wrote:

quoted

With the patch to allow xattr/attr operations if a portable signature
verification fails, cp and tar can copy all xattrs/attrs so that at the
end of the process verification succeeds.

However, it might happen that the xattrs/attrs are already set to the
correct value (taken at signing time) and signature verification succeeds
before the copy has completed. For example, an archive might contains

files

quoted

quoted

quoted

owned by root and the archive is extracted by root.

Then, since portable signatures are immutable, all subsequent operations
fail (e.g. fchown()), even if the operation is legitimate (does not alter
the current value).

This patch avoids this problem by reporting successful operation to user
space when that operation does not alter the current value of

xattrs/attrs.

quoted

quoted

I must be missing something.  If both the IMA and EVM status flags are
reset after xattr or attr modification, do we really need to prevent
any metadata - same or different - changes?  Both evm_protect_xattr()
and evm_inode_setattr() would need to be modified to allow
INTEGRITY_PASS_IMMUTABLE.

yes, given that the IMA and EVM flags are reset, it should not be
a problem to allow changes. However, I think it is useful to keep
the current behavior. For example, it would prevent an accidental
change of the SELinux label during the relabeling process.

I understand we might want to prevent accidental or malicious changes,
but that isn't the purpose of this patch set.  The patch description
would also need to be updated to reflect the real purpose.

We would be changing the expectation that metadata changes
are denied, which was defined with the original patches.

I would prefer to keep the current behavior, but if your suggestion
is to allow metadata changes, I will modify the patch set.