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

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Message-ID: <ZypJ4ZnR0JkPedNz@nanopsycho.orion>
Date: Tue, 5 Nov 2024 17:37:53 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Dmitry Antipov <dmantipov@...dex.ru>
Cc: Robin van der Gracht <robin@...tonic.nl>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Marc Kleine-Budde <mkl@...gutronix.de>, linux-can@...r.kernel.org,
	netdev@...r.kernel.org, lvc-project@...uxtesting.org,
	syzbot+d4e8dc385d9258220c31@...kaller.appspotmail.com
Subject: Re: [PATCH v2] can: fix skb reference counting in j1939_session_new()

Tue, Nov 05, 2024 at 10:48:23AM CET, dmantipov@...dex.ru wrote:
>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

It is odd to write "I assume" for fix like this. You should know for
sure, don't you?


>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
>
>