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Subject: media: vivid: Fix wrong locking that causes race conditions on streaming stop Author: Alexander Popov alex.popov@linux.com Date: Sun Nov 3 23:17:19 2019 +0100
There is the same incorrect approach to locking implemented in vivid_stop_generating_vid_cap(), vivid_stop_generating_vid_out() and sdr_cap_stop_streaming().
These functions are called during streaming stopping with vivid_dev.mutex locked. And they all do the same mistake while stopping their kthreads, which need to lock this mutex as well. See the example from vivid_stop_generating_vid_cap(): /* shutdown control thread */ vivid_grab_controls(dev, false); mutex_unlock(&dev->mutex); kthread_stop(dev->kthread_vid_cap); dev->kthread_vid_cap = NULL; mutex_lock(&dev->mutex);
But when this mutex is unlocked, another vb2_fop_read() can lock it instead of vivid_thread_vid_cap() and manipulate the buffer queue. That causes a use-after-free access later.
To fix those issues let's: 1. avoid unlocking the mutex in vivid_stop_generating_vid_cap(), vivid_stop_generating_vid_out() and sdr_cap_stop_streaming(); 2. use mutex_trylock() with schedule_timeout_uninterruptible() in the loops of the vivid kthread handlers.
Signed-off-by: Alexander Popov alex.popov@linux.com Acked-by: Linus Torvalds torvalds@linux-foundation.org Tested-by: Hans Verkuil hverkuil-cisco@xs4all.nl Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Cc: stable@vger.kernel.org # for v3.18 and up Signed-off-by: Mauro Carvalho Chehab mchehab@kernel.org
drivers/media/platform/vivid/vivid-kthread-cap.c | 8 +++++--- drivers/media/platform/vivid/vivid-kthread-out.c | 8 +++++--- drivers/media/platform/vivid/vivid-sdr-cap.c | 8 +++++--- 3 files changed, 15 insertions(+), 9 deletions(-)
---
diff --git a/drivers/media/platform/vivid/vivid-kthread-cap.c b/drivers/media/platform/vivid/vivid-kthread-cap.c index 9f981e8bae6e..01a9d671b947 100644 --- a/drivers/media/platform/vivid/vivid-kthread-cap.c +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c @@ -818,7 +818,11 @@ static int vivid_thread_vid_cap(void *data) if (kthread_should_stop()) break;
- mutex_lock(&dev->mutex); + if (!mutex_trylock(&dev->mutex)) { + schedule_timeout_uninterruptible(1); + continue; + } + cur_jiffies = jiffies; if (dev->cap_seq_resync) { dev->jiffies_vid_cap = cur_jiffies; @@ -998,8 +1002,6 @@ void vivid_stop_generating_vid_cap(struct vivid_dev *dev, bool *pstreaming)
/* shutdown control thread */ vivid_grab_controls(dev, false); - mutex_unlock(&dev->mutex); kthread_stop(dev->kthread_vid_cap); dev->kthread_vid_cap = NULL; - mutex_lock(&dev->mutex); } diff --git a/drivers/media/platform/vivid/vivid-kthread-out.c b/drivers/media/platform/vivid/vivid-kthread-out.c index c974235d7de3..6780687978f9 100644 --- a/drivers/media/platform/vivid/vivid-kthread-out.c +++ b/drivers/media/platform/vivid/vivid-kthread-out.c @@ -166,7 +166,11 @@ static int vivid_thread_vid_out(void *data) if (kthread_should_stop()) break;
- mutex_lock(&dev->mutex); + if (!mutex_trylock(&dev->mutex)) { + schedule_timeout_uninterruptible(1); + continue; + } + cur_jiffies = jiffies; if (dev->out_seq_resync) { dev->jiffies_vid_out = cur_jiffies; @@ -344,8 +348,6 @@ void vivid_stop_generating_vid_out(struct vivid_dev *dev, bool *pstreaming)
/* shutdown control thread */ vivid_grab_controls(dev, false); - mutex_unlock(&dev->mutex); kthread_stop(dev->kthread_vid_out); dev->kthread_vid_out = NULL; - mutex_lock(&dev->mutex); } diff --git a/drivers/media/platform/vivid/vivid-sdr-cap.c b/drivers/media/platform/vivid/vivid-sdr-cap.c index 9acc709b0740..2b7522e16efc 100644 --- a/drivers/media/platform/vivid/vivid-sdr-cap.c +++ b/drivers/media/platform/vivid/vivid-sdr-cap.c @@ -141,7 +141,11 @@ static int vivid_thread_sdr_cap(void *data) if (kthread_should_stop()) break;
- mutex_lock(&dev->mutex); + if (!mutex_trylock(&dev->mutex)) { + schedule_timeout_uninterruptible(1); + continue; + } + cur_jiffies = jiffies; if (dev->sdr_cap_seq_resync) { dev->jiffies_sdr_cap = cur_jiffies; @@ -303,10 +307,8 @@ static void sdr_cap_stop_streaming(struct vb2_queue *vq) }
/* shutdown control thread */ - mutex_unlock(&dev->mutex); kthread_stop(dev->kthread_sdr_cap); dev->kthread_sdr_cap = NULL; - mutex_lock(&dev->mutex); }
static void sdr_cap_buf_request_complete(struct vb2_buffer *vb)