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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Petar Penkov <ppenkov@aviatrix.com>,
        Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH 5.4 14/58] net: tun: stop NAPI when detaching queues
Date:   Tue,  5 Jul 2022 13:57:50 +0200
Message-Id: <20220705115610.663956499@linuxfoundation.org>
In-Reply-To: <20220705115610.236040773@linuxfoundation.org>
References: <20220705115610.236040773@linuxfoundation.org>
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From: Jakub Kicinski <kuba@kernel.org>

commit a8fc8cb5692aebb9c6f7afd4265366d25dcd1d01 upstream.

While looking at a syzbot report I noticed the NAPI only gets
disabled before it's deleted. I think that user can detach
the queue before destroying the device and the NAPI will never
be stopped.

Fixes: 943170998b20 ("tun: enable NAPI for TUN/TAP driver")
Acked-by: Petar Penkov <ppenkov@aviatrix.com>
Link: https://lore.kernel.org/r/20220623042105.2274812-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/tun.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -327,6 +327,12 @@ static void tun_napi_init(struct tun_str
 	}
 }
 
+static void tun_napi_enable(struct tun_file *tfile)
+{
+	if (tfile->napi_enabled)
+		napi_enable(&tfile->napi);
+}
+
 static void tun_napi_disable(struct tun_file *tfile)
 {
 	if (tfile->napi_enabled)
@@ -709,8 +715,10 @@ static void __tun_detach(struct tun_file
 		if (clean) {
 			RCU_INIT_POINTER(tfile->tun, NULL);
 			sock_put(&tfile->sk);
-		} else
+		} else {
 			tun_disable_queue(tun, tfile);
+			tun_napi_disable(tfile);
+		}
 
 		synchronize_net();
 		tun_flow_delete_by_queue(tun, tun->numqueues + 1);
@@ -864,6 +872,7 @@ static int tun_attach(struct tun_struct
 
 	if (tfile->detached) {
 		tun_enable_queue(tfile);
+		tun_napi_enable(tfile);
 	} else {
 		sock_hold(&tfile->sk);
 		tun_napi_init(tun, tfile, napi, napi_frags);