[PATCH 5.15 58/98] net: tun: avoid disabling NAPI twice

Greg Kroah-Hartman
2022-07-05T12:31:10Z

From: Jakub Kicinski <kuba@kernel.org>

commit ff1fa2081d173b01cebe2fbf0a2d0f1cee9ce4b5 upstream.

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/tun.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -641,7 +641,8 @@ static void __tun_detach(struct tun_file
tun = rtnl_dereference(tfile->tun);

if (tun && clean) {
- tun_napi_disable(tfile);
+ if (!tfile->detached)
+ tun_napi_disable(tfile);
tun_napi_del(tfile);
}