From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> [ 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@xxxxxxxxxx/ Reported-by: syzbot+3f91de0b813cc3d19a80@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 3823ab2c4e4be..cec3f56739dc2 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; } -- 2.33.0
