evm: Fix RCU list related warnings

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>

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 77ad1e5..2e1597e 100644 (file)
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -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)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index d361d7f..0d36259 100644 (file)
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -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;

diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index 39ad103..cfc3075 100644 (file)
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c
@@ -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) {