[PATCH AUTOSEL 5.4 03/26] evm: Fix RCU list related warnings
From: Sasha Levin <sashal@kernel.org>
Date: 2020-05-28 12:05:36
Also in:
lkml, stable
Subsystem:
extended verification module (evm), integrity measurement architecture (ima), security subsystem, the rest · Maintainers:
Mimi Zohar, Roberto Sassu, Dmitry Kasatkin, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
From: Madhuparna Bhowmik <redacted> [ Upstream commit 770f60586d2af0590be263f55fd079226313922c ] This patch fixes the following warning and few other instances of traversal of evm_config_xattrnames list: [ 32.848432] ============================= [ 32.848707] WARNING: suspicious RCU usage [ 32.848966] 5.7.0-rc1-00006-ga8d5875ce5f0b #1 Not tainted [ 32.849308] ----------------------------- [ 32.849567] security/integrity/evm/evm_main.c:231 RCU-list traversed in non-reader section!! Since entries are only added to the list and never deleted, use list_for_each_entry_lockless() instead of list_for_each_entry_rcu for traversing the list. Also, add a relevant comment in evm_secfs.c to indicate this fact. Reported-by: kernel test robot <redacted> Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Madhuparna Bhowmik <redacted> Acked-by: Paul E. McKenney <paulmck@kernel.org> (RCU viewpoint) Signed-off-by: Mimi Zohar <zohar@linux.ibm.com> Signed-off-by: Sasha Levin <sashal@kernel.org> --- security/integrity/evm/evm_crypto.c | 2 +- security/integrity/evm/evm_main.c | 4 ++-- security/integrity/evm/evm_secfs.c | 9 ++++++++- 3 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index cc826c2767a3..fbc2ee6d46fc 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c@@ -209,7 +209,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry, data->hdr.length = crypto_shash_digestsize(desc->tfm); error = -ENODATA; - list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { bool is_ima = false; if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index f9a81b187fae..a2c393385db0 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c@@ -99,7 +99,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry) if (!(inode->i_opflags & IOP_XATTR)) return -EOPNOTSUPP; - list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0); if (error < 0) { if (error == -ENODATA)
@@ -230,7 +230,7 @@ static int evm_protected_xattr(const char *req_xattr_name) struct xattr_list *xattr; namelen = strlen(req_xattr_name); - list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { if ((strlen(xattr->name) == namelen) && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) { found = 1;
diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index c11c1f7b3ddd..0f37ef27268d 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c@@ -234,7 +234,14 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf, goto out; } - /* Guard against races in evm_read_xattrs */ + /* + * xattr_list_mutex guards against races in evm_read_xattrs(). + * Entries are only added to the evm_config_xattrnames list + * and never deleted. Therefore, the list is traversed + * using list_for_each_entry_lockless() without holding + * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs() + * and evm_protected_xattr(). + */ mutex_lock(&xattr_list_mutex); list_for_each_entry(tmp, &evm_config_xattrnames, list) { if (strcmp(xattr->name, tmp->name) == 0) {
--
2.25.1