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Message-ID: <18aa0617-0afe-2543-89cf-2f04c682ea88@ispras.ru>
Date:   Fri, 5 Aug 2022 11:56:18 +0300
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Subject: Re: [PATCH] can: j1939: fix memory leak of skbs
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To:     Oleksij Rempel <o.rempel@pengutronix.de>
Cc:     Robin van der Gracht <robin@protonic.nl>,
        Oleksij Rempel <linux@rempel-privat.de>, kernel@pengutronix.de,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-can@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        ldv-project@linuxtesting.org,
        Alexey Khoroshilov <khoroshilov@ispras.ru>
References: <20220708175949.539064-1-pchelkin@ispras.ru>
 <20220729042244.GC30201@pengutronix.de>
From:   Fedor Pchelkin <pchelkin@ispras.ru>
In-Reply-To: <20220729042244.GC30201@pengutronix.de>
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Hi Oleksij,

On 29.07.2022 07:22, Oleksij Rempel wrote:
> Initial issue can be reproduced by using real (slow) CAN with j1939cat[1]
> tool. Both parts should be started to make sure the j1939_session_tx_dat() will
> actually start using the queue. After pushing about 100K of data, application
> will try to close the socket and exit. After socket is closed, all skb related
> to this socket will be freed and j1939_session_tx_dat() will use freed skbs.

Ok, the patch I suggested was a kind of a guess, now I understand that
it breaks important logic.

On 29.07.2022 07:22, Oleksij Rempel wrote:
 > This skb_get() is counter part of skb_unref()
 > j1939_session_skb_drop_old().

However, we have a case [1] where j1939_session_skb_queue() is called
but the corresponding j1939_session_skb_drop_old() is not called and it
causes a memory leak.

I tried to investigate it a little bit: the thing is that
j1939_session_skb_drop_old() can be called only when processing
J1939_ETP_CMD_CTS. On the contrary, as I can see,
j1939_session_skb_queue() can be called independently from
J1939_ETP_CMD_CTS so the two functions obviously do not correspond to
each other.

In reproducer case there is a J1939_ETP_CMD_RTS processing, then
we send some messages (where j1939_session_skb_queue() is called) and
after that J1939_ETP_CMD_ABORT is processed and we lose those skbs.

[1] https://forge.ispras.ru/issues/11743