bap: Fix not checking if request fits when grouping

When grouping requests with the same opcode the code was queueing them
without attempt to check that that would fit in the ATT MTU causing the
following trace:

stack-buffer-overflow on address 0x7fffdba951f0 at pc 0x7fc15fc49d21 bp
0x7fffdba95020 sp 0x7fffdba947d0
WRITE of size 9 at 0x7fffdba951f0 thread T0
   #0 0x7fc15fc49d20 in __interceptor_memcpy
(/lib64/libasan.so.8+0x49d20)
   #1 0x71f698 in util_iov_push_mem src/shared/util.c:266
   #2 0x7b9312 in append_group src/shared/bap.c:3424
   #3 0x71ba01 in queue_foreach src/shared/queue.c:207
   #4 0x7b9b66 in bap_send src/shared/bap.c:3459
   #5 0x7ba594 in bap_process_queue src/shared/bap.c:351

Fixes: bluez/bluez#457 (comment)

src/shared/bap.c

@@ -3425,27 +3425,44 @@ static void append_group(void *data, void *user_data)
 					req->iov[i].iov_base);
 }
 
+static uint16_t bap_req_len(struct bt_bap_req *req)
+{
+	uint16_t len = 0;
+	size_t i;
+	const struct queue_entry *e;
+
+	for (i = 0; i < req->len; i++)
+		len += req->iov[i].iov_len;
+
+	e = queue_get_entries(req->group);
+	for (; e; e = e->next)
+		len += bap_req_len(e->data);
+
+	return len;
+}
+
 static bool bap_send(struct bt_bap *bap, struct bt_bap_req *req)
 {
 	struct bt_ascs *ascs = bap_get_ascs(bap);
 	int ret;
 	uint16_t handle;
-	uint8_t buf[64];
 	struct bt_ascs_ase_hdr hdr;
-	struct iovec iov  = {
-		.iov_base = buf,
-		.iov_len = 0,
-	};
+	struct iovec iov;
 	size_t i;
 
-	DBG(bap, "req %p", req);
+	iov.iov_len = sizeof(hdr) + bap_req_len(req);
+
+	DBG(bap, "req %p len %u", req, iov.iov_len);
 
 	if (!gatt_db_attribute_get_char_data(ascs->ase_cp, NULL, &handle,
 						NULL, NULL, NULL)) {
 		DBG(bap, "Unable to find Control Point");
 		return false;
 	}
 
+	iov.iov_base = alloca(iov.iov_len);
+	iov.iov_len = 0;
+
 	hdr.op = req->op;
 	hdr.num = 1 + queue_length(req->group);
 
@@ -3531,9 +3548,19 @@ static bool bap_queue_req(struct bt_bap *bap, struct bt_bap_req *req)
 {
 	struct bt_bap_req *pend;
 	struct queue *queue;
+	struct bt_att *att = bt_bap_get_att(bap);
+	uint16_t mtu = bt_att_get_mtu(att);
+	uint16_t len = 2 + bap_req_len(req);
+
+	if (len > mtu) {
+		DBG(bap, "Unable to queue request: req len %u > %u mtu", len,
+									mtu);
+		return false;
+	}
 
 	pend = queue_find(bap->reqs, match_req, req);
-	if (pend) {
+	/* Check if req can be grouped together and it fits in the MTU */
+	if (pend && (bap_req_len(pend) + len < mtu)) {
 		if (!pend->group)
 			pend->group = queue_new();
 		/* Group requests with the same opcode */