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evm: Fix RCU list related warnings

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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 <lkp@intel.com>
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org> (RCU viewpoint)
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Madhuparna Bhowmik 2020-04-30 21:32:05 +05:30 committed by Mimi Zohar
parent 2e3a34e9f4
commit 770f60586d
3 changed files with 11 additions and 4 deletions
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2
security/integrity/evm/evm_crypto.c
View File

@ -207,7 +207,7 @@ 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)

4
security/integrity/evm/evm_main.c
View File

@ -97,7 +97,7 @@ 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)
@ -228,7 +228,7 @@ 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;

9
security/integrity/evm/evm_secfs.c
View File

@ -232,7 +232,14 @@ 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) {