[PATCH] can: fix skb reference counting in j1939_session_new()

[Dmitry Antipov]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=d4e8dc385d9258220c31
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Dmitry Antipov <dmantipov@xxxxxxxxx>
---
 net/can/j1939/transport.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 319f47df3330..fecee36dbb70 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -1505,7 +1505,8 @@ 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);
+	/* Take an extra ref just like in j1939_session_skb_queue(). */
+	skb_queue_tail(&session->skb_queue, skb_get(skb));
 
 	skcb = j1939_skb_to_cb(skb);
 	memcpy(&session->skcb, skcb, sizeof(session->skcb));
-- 
2.46.2