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: 6760cd5a7546 ("net: tun: stop NAPI when detaching queues")
Reported-by: syzbot <syzkaller@googlegroups.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20220629181911.372047-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e2eb35887394e384972f573745f5870ba8c9d19b..259b2b84b2b39453cb3de27c632cf9bc0f9ce2b7 100644 (file)
--- 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);
        }