[PATCH] media: dvb-core: protect dvr_buffer reinitialization with lock

[Soham Kute <officialsohamkute@gmail.com>]

dvb_dvr_open() updates dvr_buffer fields without holding
dmxdev->lock. This can race with concurrent readers and
lead to inconsistent ringbuffer state.

Protect dvr_buffer reinitialization with spin_lock_irq()
to serialize against concurrent access.

Reported-by: syzbot+ab12f0c08dd7ab8d057c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ab12f0c08dd7ab8d057c
Signed-off-by: Soham Kute <officialsohamkute@gmail.com>
---
 drivers/media/dvb-core/dmxdev.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index 8c6f5aafd..e5e666866 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -168,7 +168,12 @@ static int dvb_dvr_open(struct inode *inode, struct file *file)
 			mutex_unlock(&dmxdev->mutex);
 			return -ENOMEM;
 		}
-		dvb_ringbuffer_init(&dmxdev->dvr_buffer, mem, DVR_BUFFER_SIZE);
+		spin_lock_irq(&dmxdev->lock);
+		dmxdev->dvr_buffer.data = mem;
+		dmxdev->dvr_buffer.size = DVR_BUFFER_SIZE;
+		dvb_ringbuffer_reset(&dmxdev->dvr_buffer);
+		spin_unlock_irq(&dmxdev->lock);
+
 		if (dmxdev->may_do_mmap)
 			dvb_vb2_init(&dmxdev->dvr_vb2_ctx, "dvr",
 				     file->f_flags & O_NONBLOCK);
-- 
2.34.1