tree b5cdc1b59f56649c5c95322ef91cf898f2d2afc9
parent c1ced46c7b49ad7bc064e68d966e0ad303f917fb
author Hans Verkuil <hverkuil@xs4all.nl> 1542625740 -0500
committer Mauro Carvalho Chehab <mchehab+samsung@kernel.org> 1555948207 -0400

media: vb2: add waiting_in_dqbuf flag

Calling VIDIOC_DQBUF can release the core serialization lock pointed to
by vb2_queue->lock if it has to wait for a new buffer to arrive.

However, if userspace dup()ped the video device filehandle, then it is
possible to read or call DQBUF from two filehandles at the same time.

It is also possible to call REQBUFS from one filehandle while the other
is waiting for a buffer. This will remove all the buffers and reallocate
new ones. Removing all the buffers isn't the problem here (that's already
handled correctly by DQBUF), but the reallocating part is: DQBUF isn't
aware that the buffers have changed.

This is fixed by setting a flag whenever the lock is released while waiting
for a buffer to arrive. And checking the flag where needed so we can return
-EBUSY.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Reported-by: Syzbot <syzbot+4180ff9ca6810b06c1e9@syzkaller.appspotmail.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>