From: Casey Schaufler [mailto:casey@schaufler-ca.com]
Sent: Wednesday, April 7, 2021 6:18 PM
On 4/7/2021 3:52 AM, Roberto Sassu wrote:

quoted

ima_inode_setxattr() and ima_inode_removexattr() hooks are called

before an

quoted

operation is performed. Thus, ima_reset_appraise_flags() should not be
called there, as flags might be unnecessarily reset if the operation is
denied.

This patch introduces the post hooks ima_inode_post_setxattr() and
ima_inode_post_removexattr(), and adds the call to
ima_reset_appraise_flags() in the new functions.

Cc: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 fs/xattr.c                            |  2 ++
 include/linux/ima.h                   | 18 ++++++++++++++++++
 security/integrity/ima/ima_appraise.c | 25 ++++++++++++++++++++++--

-

quoted

 security/security.c                   |  1 +
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index b3444e06cded..81847f132d26 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c

@@ -16,6 +16,7 @@
 #include <linux/namei.h>
 #include <linux/security.h>
 #include <linux/evm.h>
+#include <linux/ima.h>
 #include <linux/syscalls.h>
 #include <linux/export.h>
 #include <linux/fsnotify.h>

@@ -502,6 +503,7 @@ __vfs_removexattr_locked(struct

user_namespace *mnt_userns,

quoted

 	if (!error) {
 		fsnotify_xattr(dentry);
+		ima_inode_post_removexattr(dentry, name);
 		evm_inode_post_removexattr(dentry, name);
 	}

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 61d5723ec303..5e059da43857 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h

@@ -171,7 +171,13 @@ extern void ima_inode_post_setattr(struct

user_namespace *mnt_userns,

quoted

 				   struct dentry *dentry);
 extern int ima_inode_setxattr(struct dentry *dentry, const char

*xattr_name,

quoted

 		       const void *xattr_value, size_t xattr_value_len);
+extern void ima_inode_post_setxattr(struct dentry *dentry,
+				    const char *xattr_name,
+				    const void *xattr_value,
+				    size_t xattr_value_len);
 extern int ima_inode_removexattr(struct dentry *dentry, const char

*xattr_name);

quoted

+extern void ima_inode_post_removexattr(struct dentry *dentry,
+				       const char *xattr_name);
 #else
 static inline bool is_ima_appraise_enabled(void)
 {

@@ -192,11 +198,23 @@ static inline int ima_inode_setxattr(struct dentry

*dentry,

quoted

 	return 0;
 }

+static inline void ima_inode_post_setxattr(struct dentry *dentry,
+					   const char *xattr_name,
+					   const void *xattr_value,
+					   size_t xattr_value_len)
+{
+}
+
 static inline int ima_inode_removexattr(struct dentry *dentry,
 					const char *xattr_name)
 {
 	return 0;
 }
+
+static inline void ima_inode_post_removexattr(struct dentry *dentry,
+					      const char *xattr_name)
+{
+}
 #endif /* CONFIG_IMA_APPRAISE */

 #if defined(CONFIG_IMA_APPRAISE) &&

defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)

quoted

diff --git a/security/integrity/ima/ima_appraise.c

b/security/integrity/ima/ima_appraise.c

quoted

index 565e33ff19d0..1f029e4c8d7f 100644

--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c

@@ -577,21 +577,40 @@ int ima_inode_setxattr(struct dentry *dentry,

const char *xattr_name,

quoted

 	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;
 	}
 	return result;
 }

+void ima_inode_post_setxattr(struct dentry *dentry, const char

*xattr_name,

quoted

+			     const void *xattr_value, size_t xattr_value_len)
+{
+	const struct evm_ima_xattr_data *xvalue = xattr_value;
+	int result;
+
+	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
+				   xattr_value_len);
+	if (result == 1)
+		ima_reset_appraise_flags(d_backing_inode(dentry),
+			xvalue->type == EVM_IMA_XATTR_DIGSIG);
+}
+

Now you're calling ima_protect_xattr() twice for each setxattr.
Is that safe? Is it performant? Does it matter?

Hi Casey

I would expect that this does not have a significant impact on
the performance (it is just a strcmp on the xattr name).

Thanks

Roberto

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

quoted

 int ima_inode_removexattr(struct dentry *dentry, const char

*xattr_name)

quoted

 {
 	int result;

 	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
 	if (result == 1) {
-		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
 		result = 0;
 	}
 	return result;
 }
+
+void ima_inode_post_removexattr(struct dentry *dentry, const char

*xattr_name)

quoted

+{
+	int result;
+
+	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
+	if (result == 1)
+		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
+}

Now you're calling ima_protect_xattr() twice for each removexattr.
Is that safe? Is it performant? Does it matter?

quoted

diff --git a/security/security.c b/security/security.c
index 5ac96b16f8fa..efb1f874dc41 100644
--- a/security/security.c
+++ b/security/security.c

@@ -1319,6 +1319,7 @@ void security_inode_post_setxattr(struct dentry

*dentry, const char *name,

quoted

 	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
 		return;
 	call_void_hook(inode_post_setxattr, dentry, name, value, size,

flags);

quoted

+	ima_inode_post_setxattr(dentry, name, value, size);
 	evm_inode_post_setxattr(dentry, name, value, size);
 }