From 8ed576395f6a9dbf8ce39351d00cc83e093b4598 Mon Sep 17 00:00:00 2001

From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

Date: Sat, 28 Aug 2021 23:41:40 -0700

Subject: [PATCH] smackfs: Fix use-after-free in netlbl_catmap_walk()

Git-commit: 0817534ff9ea809fac1322c5c8c574be8483ea57

Patch-mainline: v5.16-rc1

References: stable-5.14.19

[ Upstream commit 0817534ff9ea809fac1322c5c8c574be8483ea57 ]

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 reader(s) using the same 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 should be 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>

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 security/smack/smackfs.c | 5 ++++-

 1 file changed, 4 insertions(+), 1 deletion(-)

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.

-- 

2.26.2