linux-kernel - Re: [PATCH] media: ti-vpe: cal: Fix a NULL pointer dereference in cal_ctx_v4l2_init

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Date:   Wed, 26 Jan 2022 02:39:41 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Benoit Parrot <bparrot@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: ti-vpe: cal: Fix a NULL pointer dereference in
 cal_ctx_v4l2_init_formats()

Hi Zhou,

Thank you for the patch.

On Tue, Jan 25, 2022 at 01:20:01AM +0800, Zhou Qingyang wrote:
> In cal_ctx_v4l2_init_formats(), devm_kzalloc() is assigned to fw and there

What do you mean by "fw" here ? It could be replaced with "is assigned
to ctx->active_fmt". If you're fine with this change, there's no need to
resend, I can fix this when applying.

> is a dereference of it after that, which could lead to NULL pointer
> dereference on failure of devm_kzalloc().
> 
> Fix this bug by adding a NULL check of ctx->active_fmt.
> 
> This bug was found by a static analyzer.
> 
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: 7168155002cf ("media: ti-vpe: cal: Move format handling to cal.c and expose helpers")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> --
> The analysis employs differential checking to identify inconsistent 
> security operations (e.g., checks or kfrees) between two code paths 
> and confirms that the inconsistent operations are not recovered in the
> current function or the callers, so they constitute bugs. 
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
>  drivers/media/platform/ti-vpe/cal-video.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/platform/ti-vpe/cal-video.c b/drivers/media/platform/ti-vpe/cal-video.c
> index 7799da1cc261..3e936a2ca36c 100644
> --- a/drivers/media/platform/ti-vpe/cal-video.c
> +++ b/drivers/media/platform/ti-vpe/cal-video.c
> @@ -823,6 +823,9 @@ static int cal_ctx_v4l2_init_formats(struct cal_ctx *ctx)
>  	/* Enumerate sub device formats and enable all matching local formats */
>  	ctx->active_fmt = devm_kcalloc(ctx->cal->dev, cal_num_formats,
>  				       sizeof(*ctx->active_fmt), GFP_KERNEL);
> +	if (!ctx->active_fmt)
> +		return -ENOMEM;
> +
>  	ctx->num_active_fmt = 0;
>  
>  	for (j = 0, i = 0; ; ++j) {

-- 
Regards,

Laurent Pinchart