res_rtp_asterisk.c: Fix off-nominal crash potential.

ASTERISK-25296
Reported by: Richard Mudgett

Change-Id: I08549fb7c3ab40a559f41a3940f3732a4059b55b

diff --git a/res/res_rtp_asterisk.c b/res/res_rtp_asterisk.c
index 5d206c1a0201a04b9b6677bd9fdbb96c7e36315c..00617e4e7d1fc805b90dc36258374bc35a20e695 100644 (file)
--- a/res/res_rtp_asterisk.c
+++ b/res/res_rtp_asterisk.c
@@ -4504,6 +4504,10 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
        }
 
        payload = ast_rtp_codecs_get_payload(ast_rtp_instance_get_codecs(instance), payloadtype);
+       if (!payload) {
+               /* Unknown payload type. */
+               return AST_LIST_FIRST(&frames) ? AST_LIST_FIRST(&frames) : &ast_null_frame;
+       }
 
        /* If the payload is not actually an Asterisk one but a special one pass it off to the respective handler */
        if (!payload->asterisk_format) {
@@ -4530,10 +4534,7 @@ static struct ast_frame *ast_rtp_read(struct ast_rtp_instance *instance, int rtc
                /* Even if no frame was returned by one of the above methods,
                 * we may have a frame to return in our frame list
                 */
-               if (!AST_LIST_EMPTY(&frames)) {
-                       return AST_LIST_FIRST(&frames);
-               }
-               return &ast_null_frame;
+               return AST_LIST_FIRST(&frames) ? AST_LIST_FIRST(&frames) : &ast_null_frame;
        }
 
        ao2_replace(rtp->lastrxformat, payload->format);