linux-kernel - [PATCH 5.4 28/58] net: tun: avoid disabling NAPI twice

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Message-Id: <20220705115611.074797102@linuxfoundation.org>
Date:   Tue,  5 Jul 2022 13:58:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, syzbot <syzkaller@...glegroups.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 5.4 28/58] net: tun: avoid disabling NAPI twice

From: Jakub Kicinski <kuba@...nel.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@...glegroups.com>
Reported-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Link: https://lore.kernel.org/r/20220629181911.372047-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/tun.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -696,7 +696,8 @@ 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);
 	}