[PATCH v2 1/2] ALSA: usbusx2y: fix in04_last array size mismatch with in04_buf

[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 is allocated as sizeof(struct us428_ctls) which is 21 bytes.
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 source object.

Introduce a USX2Y_IN04_SIZE constant defined as sizeof(struct
us428_ctls) and use it consistently for the in04_last array, the
in04_buf allocation, the URB transfer length, and the comparison loop,
replacing the bare 24 and 21 literals throughout.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
v2: Introduce USX2Y_IN04_SIZE constant and replace all magic number
    occurrences, per Takashi Iwai review [Takashi Iwai]
 sound/usb/usx2y/usbusx2y.c | 6 +++---
 sound/usb/usx2y/usbusx2y.h | 4 +++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/sound/usb/usx2y/usbusx2y.c b/sound/usb/usx2y/usbusx2y.c
index 4190227c5a2a5..200b708aacd6d 100644
--- a/sound/usb/usx2y/usbusx2y.c
+++ b/sound/usb/usx2y/usbusx2y.c
@@ -196,7 +196,7 @@ static void i_usx2y_in04_int(struct urb *urb)
 			memcpy(usx2y->in04_last, usx2y->in04_buf, sizeof(usx2y->in04_last));
 			us428ctls->ctl_snapshot_last = -1;
 		} else {
-			for (i = 0; i < 21; i++) {
+			for (i = 0; i < USX2Y_IN04_SIZE; i++) {
 				if (usx2y->in04_last[i] != ((char *)usx2y->in04_buf)[i]) {
 					if (diff < 0)
 						diff = i;
@@ -305,7 +305,7 @@ int usx2y_in04_init(struct usx2ydev *usx2y)
 		goto error;
 	}
 
-	usx2y->in04_buf = kmalloc(21, GFP_KERNEL);
+	usx2y->in04_buf = kmalloc(USX2Y_IN04_SIZE, GFP_KERNEL);
 	if (!usx2y->in04_buf) {
 		err = -ENOMEM;
 		goto error;
@@ -313,7 +313,7 @@ int usx2y_in04_init(struct usx2ydev *usx2y)
 
 	init_waitqueue_head(&usx2y->in04_wait_queue);
 	usb_fill_int_urb(usx2y->in04_urb, usx2y->dev, usb_rcvintpipe(usx2y->dev, 0x4),
-			 usx2y->in04_buf, 21,
+			 usx2y->in04_buf, USX2Y_IN04_SIZE,
 			 i_usx2y_in04_int, usx2y,
 			 10);
 	if (usb_urb_ep_type_check(usx2y->in04_urb)) {
diff --git a/sound/usb/usx2y/usbusx2y.h b/sound/usb/usx2y/usbusx2y.h
index 6a76d04bf1c7d..7b6deed17d4b1 100644
--- a/sound/usb/usx2y/usbusx2y.h
+++ b/sound/usb/usx2y/usbusx2y.h
@@ -5,6 +5,8 @@
 #include "../midi.h"
 #include "usbus428ctldefs.h"
 
+#define USX2Y_IN04_SIZE	sizeof(struct us428_ctls)
+
 #define NRURBS	        2
 
 /* Default value used for nr of packs per urb.
@@ -55,7 +57,7 @@ struct usx2ydev {
 	int			stride;
 	struct urb		*in04_urb;
 	void			*in04_buf;
-	char			in04_last[24];
+	char			in04_last[USX2Y_IN04_SIZE];
 	unsigned int		in04_int_calls;
 	struct snd_usx2y_urb_seq	*us04;
 	wait_queue_head_t	in04_wait_queue;
-- 
2.47.3