[PATCH] media: bt8xx: Fix a possible data race in buffer_queue()

From: Tuo Li
Date: Wed Jun 28 2023 - 04:32:42 EST


The variable btv->loop_irq is often protected by the lock btv->s_lock when
is accessed. Here is an example in bttv_irq_timeout():

spin_lock_irqsave(&btv->s_lock,flags);
...
btv->loop_irq = 0;
...
spin_unlock_irqrestore(&btv->s_lock,flags);

However, it is accessed without holding the lock btv->s_lock in
buffer_queue():

btv->loop_irq |= 1;

And thus a data race can occur.
To fix this possible data race, a lock and unlock pair is added when
accessing the variable btv->loop_irq in buffer_queue().

Reported-by: BassCheck <bass@xxxxxxxxxxx>
Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
---
drivers/media/pci/bt8xx/bttv-driver.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/media/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
index 734f02b91aa3..241c51951627 100644
--- a/drivers/media/pci/bt8xx/bttv-driver.c
+++ b/drivers/media/pci/bt8xx/bttv-driver.c
@@ -1617,13 +1617,16 @@ buffer_queue(struct videobuf_queue *q, struct videobuf_buffer *vb)
struct bttv_buffer *buf = container_of(vb,struct bttv_buffer,vb);
struct bttv_fh *fh = q->priv_data;
struct bttv *btv = fh->btv;
+ unsigned long flags;

+ spin_lock_irqsave(&btv->s_lock,flags);
buf->vb.state = VIDEOBUF_QUEUED;
list_add_tail(&buf->vb.queue,&btv->capture);
if (!btv->curr.frame_irq) {
btv->loop_irq |= 1;
bttv_set_dma(btv, 0x03);
}
+ spin_unlock_irqrestore(&btv->s_lock,flags);
}

static void buffer_release(struct videobuf_queue *q, struct videobuf_buffer *vb)
--
2.34.1