[PATCH 1/2] ALSA: usbusx2y: fix in04_last array size causing slab OOB read

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

The in04_last array in struct usx2ydev is declared as char[24], but
in04_buf (the source for memcpy) is allocated with kmalloc(21).  In
i_usx2y_in04_int(), when ctl_snapshot_last == -2 (initialization path):

    memcpy(usx2y->in04_last, usx2y->in04_buf, sizeof(usx2y->in04_last));

This copies 24 bytes from a 21-byte slab allocation, reading 3 bytes
past the end of the kmalloc-32 object.

The comparison loop already uses the correct bound of 21:

    for (i = 0; i < 21; i++) {

Fix by reducing the in04_last array to 21 bytes, matching the actual
USB interrupt transfer size and the in04_buf allocation.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 sound/usb/usx2y/usbusx2y.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/usx2y/usbusx2y.h b/sound/usb/usx2y/usbusx2y.h
index 6a76d04bf1c7d..266a3483ab81c 100644
--- a/sound/usb/usx2y/usbusx2y.h
+++ b/sound/usb/usx2y/usbusx2y.h
@@ -55,7 +55,7 @@ struct usx2ydev {
 	int			stride;
 	struct urb		*in04_urb;
 	void			*in04_buf;
-	char			in04_last[24];
+	char			in04_last[21];
 	unsigned int		in04_int_calls;
 	struct snd_usx2y_urb_seq	*us04;
 	wait_queue_head_t	in04_wait_queue;
-- 
2.47.3