Messages in this thread Patch in this message | | | From | Alexander Popov <> | Subject | [PATCH v3 1/1] media: vivid: Fix wrong locking that causes race conditions on streaming stop | Date | Sat, 2 Nov 2019 22:03:27 +0300 |
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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() 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> --- 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 003319d7816d..27b9c78d2d05 100644 --- a/drivers/media/platform/vivid/vivid-kthread-cap.c +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c @@ -796,7 +796,11 @@ static int vivid_thread_vid_cap(void *data) if (kthread_should_stop()) break; - mutex_lock(&dev->mutex); + if (!mutex_trylock(&dev->mutex)) { + schedule_timeout(1); + continue; + } + cur_jiffies = jiffies; if (dev->cap_seq_resync) { dev->jiffies_vid_cap = cur_jiffies; @@ -956,8 +960,6 @@ 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 ce5bcda2348c..a657b0d20e2f 100644 --- a/drivers/media/platform/vivid/vivid-kthread-out.c +++ b/drivers/media/platform/vivid/vivid-kthread-out.c @@ -143,7 +143,11 @@ static int vivid_thread_vid_out(void *data) if (kthread_should_stop()) break; - mutex_lock(&dev->mutex); + if (!mutex_trylock(&dev->mutex)) { + schedule_timeout(1); + continue; + } + cur_jiffies = jiffies; if (dev->out_seq_resync) { dev->jiffies_vid_out = cur_jiffies; @@ -301,8 +305,6 @@ 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..590080716962 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(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) -- 2.21.0
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