[PATCH] mac80211: fix locking in ieee80211_start_ap error path

[PATCH] mac80211: fix locking in ieee80211_start_ap error path

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

We need to hold the local->mtx to release the channel context,
as even encoded by the lockdep_assert_held() there. Fix it.

Cc: stable@vger.kernel.org
Fixes: 295b02c4be74 ("mac80211: Add FILS discovery support")
Reported-by: syzbot+11c342e5e30e9539cabd@syzkaller.appspotmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git master
---
 net/mac80211/cfg.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index bd3d3195097f..2d0dd69f9753 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1264,7 +1264,10 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 	return 0;
 
 error:
+	mutex_lock(&local->mtx);
 	ieee80211_vif_release_channel(sdata);
+	mutex_unlock(&local->mtx);
+
 	return err;
 }
 
-- 
2.33.1

Re: [syzbot] WARNING in ieee80211_vif_release_channel (2)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+11c342e5e30e9539cabd@syzkaller.appspotmail.com

Tested on:

commit:         60ec7fcf qlcnic: potential dereference null pointer of..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git master
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa556098924b78f0
dashboard link: https://syzkaller.appspot.com/bug?extid=11c342e5e30e9539cabd
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1412bd93b00000

Note: testing is done by a robot and is best-effort only.