[PATCH 6.18 090/175] ALSA: usb-audio: Prevent excessive number of frames

Greg Kroah-Hartman
2026-02-09T14:32:01Z

From: Edward Adam Davis <eadavis@qq.com>

[ Upstream commit ef5749ef8b307bf8717945701b1b79d036af0a15 ]

In this case, the user constructed the parameters with maxpacksize 40
for rate 22050 / pps 1000, and packsize[0] 22 packsize[1] 23. The buffer
size for each data URB is maxpacksize * packets, which in this example
is 40 * 6 = 240; When the user performs a write operation to send audio
data into the ALSA PCM playback stream, the calculated number of frames
is packsize[0] * packets = 264, which exceeds the allocated URB buffer
size, triggering the out-of-bounds (OOB) issue reported by syzbot [1].

Added a check for the number of single data URB frames when calculating
the number of frames to prevent [1].

[1]
BUG: KASAN: slab-out-of-bounds in copy_to_urb+0x261/0x460 sound/usb/pcm.c:1487
Write of size 264 at addr ffff88804337e800 by task syz.0.17/5506
Call Trace:
copy_to_urb+0x261/0x460 sound/usb/pcm.c:1487
prepare_playback_urb+0x953/0x13d0 sound/usb/pcm.c:1611
prepare_outbound_urb+0x377/0xc50 sound/usb/endpoint.c:333

Reported-by: syzbot+6db0415d6d5c635f72cb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6db0415d6d5c635f72cb
Tested-by: syzbot+6db0415d6d5c635f72cb@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Link: https://patch.msgid.link/tencent_9AECE6CD2C7A826D902D696C289724E8120A@qq.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
sound/usb/pcm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 54d01dfd820fa..263abb36bb2d1 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1553,7 +1553,7 @@ static int prepare_playback_urb(struct snd_usb_substream *subs,

for (i = 0; i < ctx->packets; i++) {
counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, avail);
- if (counts < 0)
+ if (counts < 0 || frames + counts >= ep->max_urb_frames)
break;
/* set up descriptor */
urb->iso_frame_desc[i].offset = frames * stride;
--
2.51.0