Re: [PATCH 1/1] v4l: ioctl: Fix memory leak in video_usercopy

[Arnd Bergmann]

On Sun, Dec 20, 2020 at 12:06 PM Sakari Ailus
<sakari.ailus@xxxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> Reported-by: syzbot+1115e79c8df6472c612b@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: d14e6d76ebf7 ("[media] v4l: Add multi-planar ioctl handling code")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

>  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