linux-kernel - Re: [PATCH v2] media: meson: vdec: Fix a NULL pointer dereference in amvdec_add

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Date:   Tue, 14 Dec 2021 15:16:38 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Zhou Qingyang <zhou1615@....edu>, kjlu@....edu,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Maxime Jourdan <mjourdan@...libre.com>,
        linux-media@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: meson: vdec: Fix a NULL pointer dereference in
 amvdec_add_ts()

On Tue, Dec 14, 2021 at 02:46:13PM +0100, Mauro Carvalho Chehab wrote:
> Em Fri,  3 Dec 2021 00:03:57 +0800
> Zhou Qingyang <zhou1615@....edu> escreveu:
> 
> > In amvdec_add_ts(), there is a dereference of kzalloc(), which could lead
> > to a NULL pointer dereference on failure of kzalloc().
> > 
> > I fix this bug by adding a NULL check of new_ts.
> > 
> > This bug was found by a static analyzer. 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.
> > 
> > Builds with CONFIG_VIDEO_MESON_VDEC=m show no new warnings,
> > and our static analyzer no longer warns about this code.
> > 
> > Fixes: 876f123b8956 ("media: meson: vdec: bring up to compliance")
> > Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> > ---
> > Changes in v2:
> >   -  Delete dev_err() message
> > 
> >  drivers/staging/media/meson/vdec/vdec_helpers.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/staging/media/meson/vdec/vdec_helpers.c b/drivers/staging/media/meson/vdec/vdec_helpers.c
> > index b9125c295d1d..ac60514c475b 100644
> > --- a/drivers/staging/media/meson/vdec/vdec_helpers.c
> > +++ b/drivers/staging/media/meson/vdec/vdec_helpers.c
> > @@ -234,6 +234,9 @@ void amvdec_add_ts(struct amvdec_session *sess, u64 ts,
> >  	unsigned long flags;
> >  
> >  	new_ts = kzalloc(sizeof(*new_ts), GFP_KERNEL);
> > +	if (!new_ts)
> > +		return;
> > +
> >  	new_ts->ts = ts;
> >  	new_ts->tc = tc;
> >  	new_ts->offset = offset;
> 
> I don't think this change is ok. Sure, it needs to check if
> kzalloc() fails, but it should return -ENOMEM and the caller
> should check if it returns an error. So, I would expect
> that this patch would also touch the caller function at
> drivers/staging/media/meson/vdec/esparser.c.

This is why umn.edu emails still are in my black-hole :(