ALSA: usb-audio: Prevent excessive number of frames

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>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 54d01dfd820fa736280b9bb25fd633a80653af49..263abb36bb2d1c0493486bdf62776bb1b178b490 100644 (file)
--- 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;