Fix an integer overflow bug in avdt_msg_asmbl

Bug: 280633699
Test: manual
Ignore-AOSP-First: security
Tag: #security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:bf9449a704c2983861dbe0ede9ab660e42826179)
Merged-In: Iaa4d603921fc4ffb8cfb5783f99ec0963affd6a2
Change-Id: Iaa4d603921fc4ffb8cfb5783f99ec0963affd6a2

system/stack/avdt/avdt_msg.cc

@@ -1285,14 +1285,14 @@ BT_HDR* avdt_msg_asmbl(AvdtpCcb* p_ccb, BT_HDR* p_buf) {
        * NOTE: The buffer is allocated above at the beginning of the
        * reassembly, and is always of size BT_DEFAULT_BUFFER_SIZE.
        */
-      uint16_t buf_len = BT_DEFAULT_BUFFER_SIZE - sizeof(BT_HDR);
+      size_t buf_len = BT_DEFAULT_BUFFER_SIZE - sizeof(BT_HDR);
 
       /* adjust offset and len of fragment for header byte */
       p_buf->offset += AVDT_LEN_TYPE_CONT;
       p_buf->len -= AVDT_LEN_TYPE_CONT;
 
       /* verify length */
-      if ((p_ccb->p_rx_msg->offset + p_buf->len) > buf_len) {
+      if (((size_t) p_ccb->p_rx_msg->offset + (size_t) p_buf->len) > buf_len) {
         /* won't fit; free everything */
         AVDT_TRACE_WARNING("%s: Fragmented message too big!", __func__);
         osi_free_and_reset((void**)&p_ccb->p_rx_msg);