linux-kernel - Re: [RFC PATCH v1] can: m_can: m_can_read_fifo: fix memory leak in error branch

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Message-ID: <CAMZ6RqJ1CtphrUxRDWOKEsJF_uzoPbYD2mPiD56VvJ9qB7oxow@mail.gmail.com>
Date:   Sat, 30 Oct 2021 01:35:01 +0900
From:   Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     linux-can <linux-can@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Matt Kline <matt@...bashing.io>,
        Sean Nyekjaer <sean@...nix.com>,
        Chandrasekar Ramakrishnan <rcsekar@...sung.com>
Subject: Re: [RFC PATCH v1] can: m_can: m_can_read_fifo: fix memory leak in
 error branch

On Fri. 29 Oct 2021 at 20:34, Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> On 27.10.2021 03:09:09, Vincent Mailhol wrote:
> > In m_can_read_fifo(), if the second call to m_can_fifo_read() fails,
> > the function jump to the out_fail label and returns without calling
> > m_can_receive_skb(). This means that the skb previously allocated by
> > alloc_can_skb() is not freed. In other terms, this is a memory leak.
> >
> > This patch adds a new goto statement: out_receive_skb and do some
> > small code refactoring to fix the issue.
>
> This means we pass a skb to the user space, which contains wrong data.
> Probably 0x0, but if the CAN frame doesn't contain 0x0, it's wrong. That
> doesn't look like a good idea. If the CAN frame broke due to a CRC issue
> on the wire it is not received. IMHO it's best to discard the skb and
> return the error.

Arg... Guess I made the right choice to tag the patch as RFC...

Just one question, what is the correct function to discard the
skb? The driver uses the napi polling system (which I am not
entirely familiar with). Does it mean that the rx is not done in
IRQ context and that we can simply use kfree_skb() instead of
dev_kfree_skb_irq()?


Yours sincerely,
Vincent Mailhol