res_rtp_asterisk: Add frame list cleanups to ast_rtp_read

In Asterisk 16+, there are a few places in ast_rtp_read where we've
allocated a frame list but return a null frame instead of the list.
In these cases, any frames left in the list won't be freed.  In the
vast majority of the cases, the list is empty when we return so
there's nothing to free but there have been leaks reported in the
wild that can be traced back to frames left in the list before
returning.

The escape paths now all have logic to free frames left in the
list.

ASTERISK-28609
Reported by: Ted G

Change-Id: Ia1d7075857ebd26b47183c44b1aebb0d8f985f7a

res/res_rtp_asterisk.c

@@ -7561,7 +7561,9 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 
 	if (!rtp->recv_buffer) {
 		/* If there is no receive buffer then we can pass back the frame directly */
-		return ast_rtp_interpret(instance, srtp, &addr, read_area, res, prev_seqno);
+		frame = ast_rtp_interpret(instance, srtp, &addr, read_area, res, prev_seqno);
+		AST_LIST_INSERT_TAIL(&frames, frame, frame_list);
+		return AST_LIST_FIRST(&frames);
 	} else if (rtp->expectedrxseqno == -1 || seqno == rtp->expectedrxseqno) {
 		rtp->expectedrxseqno = seqno + 1;
 
@@ -7569,7 +7571,9 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 		 * return it directly without duplicating it.
 		 */
 		if (!ast_data_buffer_count(rtp->recv_buffer)) {
-			return ast_rtp_interpret(instance, srtp, &addr, read_area, res, prev_seqno);
+			frame = ast_rtp_interpret(instance, srtp, &addr, read_area, res, prev_seqno);
+			AST_LIST_INSERT_TAIL(&frames, frame, frame_list);
+			return AST_LIST_FIRST(&frames);
 		}
 
 		if (!AST_VECTOR_REMOVE_CMP_ORDERED(&rtp->missing_seqno, seqno, find_by_value,
@@ -7582,7 +7586,9 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 		 * chance it will be overwritten.
 		 */
 		if (!ast_data_buffer_get(rtp->recv_buffer, seqno + 1)) {
-			return ast_rtp_interpret(instance, srtp, &addr, read_area, res, prev_seqno);
+			frame = ast_rtp_interpret(instance, srtp, &addr, read_area, res, prev_seqno);
+			AST_LIST_INSERT_TAIL(&frames, frame, frame_list);
+			return AST_LIST_FIRST(&frames);
 		}
 
 		/* Otherwise we need to dupe the frame so that the potential processing of frames placed after
@@ -7696,7 +7702,12 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 		AST_VECTOR_RESET(&rtp->missing_seqno, AST_VECTOR_ELEM_CLEANUP_NOOP);
 
 		return AST_LIST_FIRST(&frames);
-	} else if (seqno < rtp->expectedrxseqno) {
+	}
+
+	/* We're finished with the frames list */
+	ast_frame_free(AST_LIST_FIRST(&frames), 0);
+
+	if (seqno < rtp->expectedrxseqno) {
 		/* If this is a packet from the past then we have received a duplicate packet, so just drop it */
 		ast_debug(2, "Received an old packet with sequence number '%d' on RTP instance '%p', dropping it\n",
 			seqno, instance);
@@ -7807,8 +7818,6 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
 				ast_rtcp_calculate_sr_rr_statistics(instance, rtcp_report, remote_address, ice, sr);
 			}
 		}
-
-		return &ast_null_frame;
 	}
 
 	return &ast_null_frame;