Re: [PATCH RFC v3] media: em28xx: Fix race condition between open and init function

[Shuah Khan]

On 4/16/21 1:33 PM, Igor Torrente wrote:
> On 4/15/21 2:25 PM, Shuah Khan wrote:
> > On 4/15/21 8:07 AM, Igor Matheus Andrade Torrente wrote:
> > > Fixes a race condition - for lack of a more precise term - between
> > > em28xx_v4l2_open and em28xx_v4l2_init, by detaching the v4l2_dev,
> > > media_pad and vdev structs from the em28xx_v4l2, and managing the
> > > lifetime of those objects more dynamicaly.
> > >
> > > The race happens when a thread[1] - containing the em28xx_v4l2_init()
> > > code - calls the v4l2_mc_create_media_graph(), and it return a error,
> > > if a thread[2] - running v4l2_open() - pass the verification point
> > > and reaches the em28xx_v4l2_open() before the thread[1] finishes
> > > the deregistration of v4l2 subsystem, the thread[1] will free all
> > > resources before the em28xx_v4l2_open() can process their things,
> > > because the em28xx_v4l2_init() has the dev->lock. And all this lead
> > > the thread[2] to cause a user-after-free.
> > >
> > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > Reported-and-tested-by: 
> > > syzbot+b2391895514ed9ef4a8e@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@xxxxxxxxx>
> > > ---
> > >
> > > V2: Add v4l2_i2c_new_subdev null check
> > >      Deal with v4l2 subdevs dependencies
> > >
> > > V3: Fix link error when compiled as a module
> > >
> > > ---
> > >   drivers/media/usb/em28xx/em28xx-camera.c |   4 +-
> > >   drivers/media/usb/em28xx/em28xx-video.c  | 300 +++++++++++++++--------
> > >   drivers/media/usb/em28xx/em28xx.h        |   6 +-
> > >   3 files changed, 209 insertions(+), 101 deletions(-)
> >
> > The changes looks good to me. Have you tried building as a modules and
> > running modprobes and rmmods? You can do that without a device.
>
> I tried and everything worked fine.

Thank you.

Reviewed-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

thanks,
-- Shuah