linux-kernel - Re: [Patch 07/16] media: ti-vpe: vpe: fix a v4l2-compliance failure causing a kernel panic

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Date:   Mon, 30 Sep 2019 10:35:05 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Benoit Parrot <bparrot@...com>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch 07/16] media: ti-vpe: vpe: fix a v4l2-compliance failure
 causing a kernel panic

On 9/27/19 8:36 PM, Benoit Parrot wrote:
> v4l2-compliance fails with this message:
> 
>    warn: v4l2-test-formats.cpp(717): \
>    	TRY_FMT cannot handle an invalid pixelformat.
>    test VIDIOC_TRY_FMT: FAIL
> 
> This causes the following kernel panic:
> 
> Unable to handle kernel paging request at virtual address 56595561
> pgd = ecd80e00
> *pgd=00000000
> Internal error: Oops: 205 [#1] PREEMPT SMP ARM
> ...
> CPU: 0 PID: 930 Comm: v4l2-compliance Not tainted \
> 	4.14.62-01715-gc8cd67f49a19 #1
> Hardware name: Generic DRA72X (Flattened Device Tree)
> task: ece44d80 task.stack: ecc6e000
> PC is at __vpe_try_fmt+0x18c/0x2a8 [ti_vpe]
> LR is at 0x8
> 
> Because the driver fails to properly check the 'num_planes' values for
> proper ranges it ends up accessing out of bound data causing the kernel
> panic.
> 
> Since this driver only handle single or dual plane pixel format, make
> sure the provided value does not exceed 2 planes.
> 
> Signed-off-by: Benoit Parrot <bparrot@...com>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...com>
> ---
>  drivers/media/platform/ti-vpe/vpe.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/ti-vpe/vpe.c b/drivers/media/platform/ti-vpe/vpe.c
> index bbbf11174e16..1278d457f753 100644
> --- a/drivers/media/platform/ti-vpe/vpe.c
> +++ b/drivers/media/platform/ti-vpe/vpe.c
> @@ -1650,7 +1650,7 @@ static int __vpe_try_fmt(struct vpe_ctx *ctx, struct v4l2_format *f,
>  			      &pix->height, MIN_H, MAX_H, H_ALIGN,
>  			      S_ALIGN);
>  
> -	if (!pix->num_planes)
> +	if (!pix->num_planes || pix->num_planes > 2)
>  		pix->num_planes = fmt->coplanar ? 2 : 1;
>  	else if (pix->num_planes > 1 && !fmt->coplanar)
>  		pix->num_planes = 1;
> 

This looks weird.

Why not just unconditionally do:

	pix->num_planes = fmt->coplanar ? 2 : 1;

Regards,

	Hans