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References: <20201220110651.13432-1-sakari.ailus@linux.intel.com>
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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Sun, 20 Dec 2020 12:36:23 +0100
Message-ID: <CAK8P3a3s=yU=PW7zLc4M83DksxAsb=v8r4U6aAySj2-nmeczjA@mail.gmail.com>
Subject: Re: [PATCH 1/1] v4l: ioctl: Fix memory leak in video_usercopy
To:     Sakari Ailus <sakari.ailus@linux.intel.com>
Cc:     Linux Media Mailing List <linux-media@vger.kernel.org>,
        syzbot <syzbot+1115e79c8df6472c612b@syzkaller.appspotmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Sun, Dec 20, 2020 at 12:06 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> When an IOCTL with argument size larger than 128 that also used array
> arguments were handled, two memory allocations were made but alas, only
> the latter one of them was released. This happened because there was only
> a single local variable to hold such a temporary allocation.
>
> Fix this by adding separate variables to hold the pointers to the
> temporary allocations.
>
> Reported-by: Arnd Bergmann <arnd@kernel.org>
> Reported-by: syzbot+1115e79c8df6472c612b@syzkaller.appspotmail.com
> Fixes: d14e6d76ebf7 ("[media] v4l: Add multi-planar ioctl handling code")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

Acked-by: Arnd Bergmann <arnd@arndb.de>

>  out:
> +       kvfree(array_buf);
>         kvfree(mbuf);

I think it would make sense to change mbuf back to kzalloc()/kfree
after this, since the size of the ioctl argument has an upper bound
of 2^_IOC_SIZEBITS (16KB), which does not need the vmalloc
path, unlike the array args.

        Arnd