linux-kernel - Re: [PATCH] media: gspca: stv06xx: Fix memleak in stv06xx subdrivers

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Date:   Fri, 23 Apr 2021 08:48:34 +0530
From:   Atul Gopinathan <atulgopinathan@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     mchehab@...nel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH] media: gspca: stv06xx: Fix memleak in stv06xx subdrivers

On Thu, Apr 22, 2021 at 09:55:11PM +0300, Pavel Skripkin wrote:
> Hi!
> 
> On Thu, 22 Apr 2021 21:37:42 +0530
> Atul Gopinathan <atulgopinathan@...il.com> wrote:
> > During probing phase of a gspca driver in "gspca_dev_probe2()", the
> > stv06xx subdrivers have certain sensor variants (namely, hdcs_1x00,
> > hdcs_1020 and pb_0100) that allocate memory for their respective
> > sensor which is passed to the "sd->sensor_priv" field. During the
> > same probe routine, after "sensor_priv" allocation, there are chances
> > of later functions invoked to fail which result in the probing
> > routine to end immediately via "goto out" path. While doing so, the
> > memory allocated earlier for the sensor isn't taken care of resulting
> > in memory leak.
> > 
> > Fix this by adding operations to the gspca, stv06xx and down to the
> > sensor levels to free this allocated memory during gspca probe
> > failure.
> > 
> > -
> > The current level of hierarchy looks something like this:
> > 
> > 	gspca (main driver) represented by struct gspca_dev
> > 	   |
> > ___________|_____________________________________
> > |	|	|	|	|		| (subdrivers)
> > 			|			  represented
> >  			stv06xx			  by "struct
> > sd" |
> >  	 _______________|_______________
> >  	 |	|	|	|	|  (sensors)
> > 	 	|			|
> >  		hdcs_1x00/1020		pb01000
> > 			|_________________|
> > 				|
> > 			These three sensor variants
> > 			allocate memory for
> > 			"sd->sensor_priv" field.
> > 
> > Here, "struct gspca_dev" is the representation used in the top level.
> > In the sub-driver levels, "gspca_dev" pointer is cast to "struct sd*",
> > something like this:
> > 
> > 	struct sd *sd = (struct sd *)gspca_dev;
> > 
> > This is possible because the first field of "struct sd" is
> > "gspca_dev":
> > 
> > 	struct sd {
> > 		struct gspca_dev;
> > 		.
> > 		.
> > 	}
> > 
> > Therefore, to deallocate the "sd->sensor_priv" fields from
> > "gspca_dev_probe2()" which is at the top level, the patch creates
> > operations for the subdrivers and sensors to be invoked from the gspca
> > driver levels. These operations essentially free the "sd->sensor_priv"
> > which were allocated by the "config" and "init_controls" operations in
> > the case of stv06xx sub-drivers and the sensor levels.
> > 
> > This patch doesn't affect other sub-drivers or even sensors who never
> > allocate memory to "sensor_priv". It has also been tested by syzbot
> > and it returned an "OK" result.
> > 
> > https://syzkaller.appspot.com/bug?id=ab69427f2911374e5f0b347d0d7795bfe384016c
> > -
> > 
> > Fixes: 4c98834addfe ("V4L/DVB (10048): gspca - stv06xx: New
> > subdriver.") Cc: stable@...r.kernel.org
> > Suggested-by: Shuah Khan <skhan@...uxfoundation.org>
> > Reported-by: syzbot+990626a4ef6f043ed4cd@...kaller.appspotmail.com
> > Tested-by: syzbot+990626a4ef6f043ed4cd@...kaller.appspotmail.com
> > Signed-off-by: Atul Gopinathan <atulgopinathan@...il.com>
> 
> AFAIK, something similar is already applied to linux-media tree
> https://git.linuxtv.org/media_tree.git/commit/?id=4f4e6644cd876c844cdb3bea2dd7051787d5ae25

Oh, my bad. Thanks for pointing it out. The syzkaller page of this bug
hasn't been updated. I will send an e-mail and mark it as fixed.

Regards,
Atul