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

[Igor Torrente]

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.

> thanks,
> -- Shuah

Thanks,
---
Igor Matheus Andrade Torrente