netdev - [PATCH v2] can: fix skb reference counting in j1939_session

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Message-ID: <20241105094823.2403806-1-dmantipov@yandex.ru>
Date: Tue,  5 Nov 2024 12:48:23 +0300
From: Dmitry Antipov <dmantipov@...dex.ru>
To: Robin van der Gracht <robin@...tonic.nl>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Marc Kleine-Budde <mkl@...gutronix.de>
Cc: linux-can@...r.kernel.org,
	netdev@...r.kernel.org,
	lvc-project@...uxtesting.org,
	Dmitry Antipov <dmantipov@...dex.ru>,
	syzbot+d4e8dc385d9258220c31@...kaller.appspotmail.com
Subject: [PATCH v2] can: fix skb reference counting in j1939_session_new()

Since 'j1939_session_skb_queue()' do an extra 'skb_get()' for each
new skb, I assume that the same should be done for an initial one
in 'j1939_session_new()' just to avoid refcount underflow.

Reported-by: syzbot+d4e8dc385d9258220c31@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d4e8dc385d9258220c31
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Dmitry Antipov <dmantipov@...dex.ru>
---
v2: resend after hitting skb refcount underflow once again when looking
around https://syzkaller.appspot.com/bug?extid=0e6ddb1ef80986bdfe64
---
 net/can/j1939/transport.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 319f47df3330..95f7a7e65a73 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -1505,7 +1505,7 @@ static struct j1939_session *j1939_session_new(struct j1939_priv *priv,
 	session->state = J1939_SESSION_NEW;
 
 	skb_queue_head_init(&session->skb_queue);
-	skb_queue_tail(&session->skb_queue, skb);
+	skb_queue_tail(&session->skb_queue, skb_get(skb));
 
 	skcb = j1939_skb_to_cb(skb);
 	memcpy(&session->skcb, skcb, sizeof(session->skcb));
-- 
2.47.0