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

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Date:   Fri, 28 Jan 2022 12:32:30 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Zhou Qingyang <zhou1615@....edu>, 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 Greg,

On Fri, Jan 28, 2022 at 11:19:36AM +0100, Greg KH wrote:
> 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
> > 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>
> > --
> > 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) {
> 
> As stated before, umn.edu is still not allowed to contribute to the
> Linux kernel.  Please work with your administration to resolve this
> issue.

I thought this had been resolved, my bad. I can drop the patch, but it
fixes a real bug (although unlikely). Should I re-author this fix ?

-- 
Regards,

Laurent Pinchart