netdev - [PATCH net 1/2] net: tun: avoid disabling NAPI twice

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Date:   Wed, 29 Jun 2022 11:19:10 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, davem@...emloft.net, pabeni@...hat.com,
        Jakub Kicinski <kuba@...nel.org>,
        syzbot <syzkaller@...glegroups.com>,
        Petar Penkov <ppenkov@...atrix.com>
Subject: [PATCH net 1/2] net: tun: avoid disabling NAPI twice

Eric reports that syzbot made short work out of my speculative
fix. Indeed when queue gets detached its tfile->tun remains,
so we would try to stop NAPI twice with a detach(), close()
sequence.

Alternative fix would be to move tun_napi_disable() to
tun_detach_all() and let the NAPI run after the queue
has been detached.

Fixes: a8fc8cb5692a ("net: tun: stop NAPI when detaching queues")
Reported-by: syzbot <syzkaller@...glegroups.com>
Reported-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
Cc: Petar Penkov <ppenkov@...atrix.com>
---
CC: ppenkov@...atrix.com
---
 drivers/net/tun.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e2eb35887394..259b2b84b2b3 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -640,7 +640,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
 	tun = rtnl_dereference(tfile->tun);
 
 	if (tun && clean) {
-		tun_napi_disable(tfile);
+		if (!tfile->detached)
+			tun_napi_disable(tfile);
 		tun_napi_del(tfile);
 	}
 
-- 
2.36.1