[PATCH] ALSA: firewire: isight: bound the sample count to the packet payload

[Maoyi Xie <maoyixie.tju@gmail.com>]

isight_packet() takes the frame count from the device iso packet and
checks it only against the device claimed iso length.

	count = be32_to_cpu(payload->sample_count);
	if (likely(count <= (length - 16) / 4))
		isight_samples(isight, payload->samples, count);

length is the iso header data_length. It can be up to 0xffff. So the
gate allows a count up to about 16379. isight_samples() then copies
count frames out of payload->samples into the PCM DMA buffer.

payload->samples holds only 2 * MAX_FRAMES_PER_PACKET values. The
device multiplexes two samples per frame. A count past
MAX_FRAMES_PER_PACKET reads past the payload. A count past the buffer
size writes past runtime->dma_area. The smallest PCM buffer is larger
than MAX_FRAMES_PER_PACKET. Bounding the count to MAX_FRAMES_PER_PACKET
keeps both the read and the write in range.

A malicious or faulty Apple iSight on the FireWire bus reaches this
during a normal capture.

Add the MAX_FRAMES_PER_PACKET bound to the gate.

Fixes: 3a691b28a0ca ("ALSA: add Apple iSight microphone driver")
Suggested-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
---
 sound/firewire/isight.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/firewire/isight.c b/sound/firewire/isight.c
index 2b7f071d593b..33c9dd48b3b0 100644
--- a/sound/firewire/isight.c
+++ b/sound/firewire/isight.c
@@ -179,7 +179,8 @@ static void isight_packet(struct fw_iso_context *context, u32 cycle,
 	if (likely(length >= 16 &&
 		   payload->signature == cpu_to_be32(0x73676874/*"sght"*/))) {
 		count = be32_to_cpu(payload->sample_count);
-		if (likely(count <= (length - 16) / 4)) {
+		if (likely(count <= (length - 16) / 4 &&
+			   count <= MAX_FRAMES_PER_PACKET)) {
 			total = be32_to_cpu(payload->sample_total);
 			if (unlikely(total != isight->total_samples)) {
 				if (!isight->first_packet)
-- 
2.34.1