[PATCH 5.4 387/389] can: j1939: j1939_session_destroy(): fix memory leak of skbs

[Greg Kroah-Hartman]

From: Fedor Pchelkin <pchelkin@xxxxxxxxx>

commit 8c21c54a53ab21842f5050fa090f26b03c0313d6 upstream.

We need to drop skb references taken in j1939_session_skb_queue() when
destroying a session in j1939_session_destroy(). Otherwise those skbs
would be lost.

Link to Syzkaller info and repro: https://forge.ispras.ru/issues/11743.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

V1: https://lore.kernel.org/all/20220708175949.539064-1-pchelkin@xxxxxxxxx

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Suggested-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
Signed-off-by: Alexey Khoroshilov <khoroshilov@xxxxxxxxx>
Acked-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20220805150216.66313-1-pchelkin@xxxxxxxxx
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/can/j1939/transport.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -260,6 +260,8 @@ static void __j1939_session_drop(struct
 
 static void j1939_session_destroy(struct j1939_session *session)
 {
+	struct sk_buff *skb;
+
 	if (session->err)
 		j1939_sk_errqueue(session, J1939_ERRQUEUE_ABORT);
 	else
@@ -270,7 +272,11 @@ static void j1939_session_destroy(struct
 	WARN_ON_ONCE(!list_empty(&session->sk_session_queue_entry));
 	WARN_ON_ONCE(!list_empty(&session->active_session_list_entry));
 
-	skb_queue_purge(&session->skb_queue);
+	while ((skb = skb_dequeue(&session->skb_queue)) != NULL) {
+		/* drop ref taken in j1939_session_skb_queue() */
+		skb_unref(skb);
+		kfree_skb(skb);
+	}
 	__j1939_session_drop(session);
 	j1939_priv_put(session->priv);
 	kfree(session);