From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit bfbc0b5b32a8f28ce284add619bf226716a59bc0 ]

dvb_dvr_open() calls dvb_ringbuffer_init() when a new reader opens the
DVR device.  dvb_ringbuffer_init() calls init_waitqueue_head(), which
reinitializes the waitqueue list head to empty.

Since dmxdev->dvr_buffer.queue is a shared waitqueue (all opens of the
same DVR device share it), this orphans any existing waitqueue entries
from io_uring poll or epoll, leaving them with stale prev/next pointers
while the list head is reset to {self, self}.

The waitqueue and spinlock in dvr_buffer are already properly
initialized once in dvb_dmxdev_init().  The open path only needs to
reset the buffer data pointer, size, and read/write positions.

Replace the dvb_ringbuffer_init() call in dvb_dvr_open() with direct
assignment of data/size and a call to dvb_ringbuffer_reset(), which
properly resets pread, pwrite, and error with correct memory ordering
without touching the waitqueue or spinlock.

Cc: stable@vger.kernel.org
Fixes: 34731df288a5f ("V4L/DVB (3501): Dmxdev: use dvb_ringbuffer")
Reported-by: syzbot+ab12f0c08dd7ab8d057c@syzkaller.appspotmail.com
Tested-by: syzbot+ab12f0c08dd7ab8d057c@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/698a26d3.050a0220.3b3015.007d.GAE@google.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jianqiang kang <jianqkang@sina.cn>
---
 drivers/media/dvb-core/dmxdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index 4989ffe2477e..a5dd2470ecbe 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -178,7 +178,9 @@ 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);
+		dmxdev->dvr_buffer.data = mem;
+		dmxdev->dvr_buffer.size = DVR_BUFFER_SIZE;
+		dvb_ringbuffer_reset(&dmxdev->dvr_buffer);
 		if (dmxdev->may_do_mmap)
 			dvb_vb2_init(&dmxdev->dvr_vb2_ctx, "dvr",
 				     file->f_flags & O_NONBLOCK);
-- 
2.34.1