relay: prevent integer overflow in relay_open()

"subbuf_size" and "n_subbufs" come from the user and they need to be
capped to prevent an integer overflow.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

kernel/relay.c

@@ -164,10 +164,14 @@ depopulate:
  */
 static struct rchan_buf *relay_create_buf(struct rchan *chan)
 {
-	struct rchan_buf *buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
-	if (!buf)
+	struct rchan_buf *buf;
+
+	if (chan->n_subbufs > UINT_MAX / sizeof(size_t *))
 		return NULL;
 
+	buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
+	if (!buf)
+		return NULL;
 	buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
 	if (!buf->padding)
 		goto free_buf;
@@ -574,6 +578,8 @@ struct rchan *relay_open(const char *base_filename,
 
 	if (!(subbuf_size && n_subbufs))
 		return NULL;
+	if (subbuf_size > UINT_MAX / n_subbufs)
+		return NULL;
 
 	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
 	if (!chan)