Commit d3a9803b authored Apr 24, 2020 by Takashi Iwai Committed by Greg Kroah-Hartman Jun 25, 2020

ALSA: usb-audio: Fix racy list management in output queue

[ Upstream commit 5b6cc38f3f3f37109ce72b60bda215a5f6892c0b ]

The linked list entry from FIFO is peeked at
queue_pending_output_urbs() but the actual element pop-out is
performed outside the spinlock, and it's potentially racy.

Do delete the link at the right place inside the spinlock.

Fixes: 8fdff6a3 ("ALSA: snd-usb: implement new endpoint streaming model")
Link: https://lore.kernel.org/r/20200424074016.14301-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 2d50acd7

sound/usb/endpoint.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -359,17 +359,17 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep)
		ep->next_packet_read_pos %= MAX_URBS;

		/* take URB out of FIFO */
		if (!list_empty(&ep->ready_playback_urbs))
		if (!list_empty(&ep->ready_playback_urbs)) {
		ctx = list_first_entry(&ep->ready_playback_urbs,
		struct snd_urb_ctx, ready_list);
		list_del_init(&ctx->ready_list);
		}
		}
		spin_unlock_irqrestore(&ep->lock, flags);

		if (ctx == NULL)
		return;

		list_del_init(&ctx->ready_list);

		/* copy over the length information */
		for (i = 0; i < packet->packets; i++)
		ctx->packet_size[i] = packet->packet_size[i];