From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, davem@davemloft.net,
kuba@kernel.org,
syzbot+3f91de0b813cc3d19a80@syzkaller.appspotmail.com,
netdev@vger.kernel.org
Subject: [PATCH] smackfs: Fix use-after-free in netlbl_catmap_walk()
Date: Wed, 1 Sep 2021 16:18:06 -0700 [thread overview]
Message-ID: <53d3eb4e5b3c6f2a0754a5be2b36c38adf32a1dd.1630537810.git.pawan.kumar.gupta@linux.intel.com> (raw)
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(-)
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.
base-commit: 7d2a07b769330c34b4deabeed939325c77a7ec2f
--
2.31.1
reply other threads:[~2021-09-01 23:16 UTC|newest]
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