diff mbox series

smackfs: Fix use-after-free in netlbl_catmap_walk()

Message ID 53d3eb4e5b3c6f2a0754a5be2b36c38adf32a1dd.1630537810.git.pawan.kumar.gupta@linux.intel.com (mailing list archive)
State Not Applicable
Headers show
Series smackfs: Fix use-after-free in netlbl_catmap_walk() | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Pawan Gupta Sept. 1, 2021, 11:18 p.m. UTC 
Syzkaller reported use-after-free bug as described in [1]. The bug is
triggered when smk_set_cipso() tries to free stale category bitmaps
while there are concurrent readers using those bitmaps.

Wait for RCU grace period to finish before freeing the category bitmaps
in smk_set_cipso(). This makes sure that there are no more readers using
the stale bitmaps and freeing them is safe.

[1] https://lore.kernel.org/netdev/000000000000a814c505ca657a4e@google.com/

Reported-by: syzbot+3f91de0b813cc3d19a80@syzkaller.appspotmail.com
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 security/smack/smackfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)


base-commit: 7d2a07b769330c34b4deabeed939325c77a7ec2f
diff mbox series

Patch

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index 3a75d2a8f517..9d853c0e55b8 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -831,6 +831,7 @@  static int smk_open_cipso(struct inode *inode, struct file *file)
 static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
 				size_t count, loff_t *ppos, int format)
 {
+	struct netlbl_lsm_catmap *old_cat;
 	struct smack_known *skp;
 	struct netlbl_lsm_secattr ncats;
 	char mapcatset[SMK_CIPSOLEN];
@@ -920,9 +921,11 @@  static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
 
 	rc = smk_netlbl_mls(maplevel, mapcatset, &ncats, SMK_CIPSOLEN);
 	if (rc >= 0) {
-		netlbl_catmap_free(skp->smk_netlabel.attr.mls.cat);
+		old_cat = skp->smk_netlabel.attr.mls.cat;
 		skp->smk_netlabel.attr.mls.cat = ncats.attr.mls.cat;
 		skp->smk_netlabel.attr.mls.lvl = ncats.attr.mls.lvl;
+		synchronize_rcu();
+		netlbl_catmap_free(old_cat);
 		rc = count;
 		/*
 		 * This mapping may have been cached, so clear the cache.