[FFmpeg-devel] [PATCH] deobfuscate ff_interleave_add_packet

Reimar Döffinger Reimar.Doeffinger
Sat Apr 11 14:54:23 CEST 2009

I propose this change:
Index: libavformat/utils.c
--- libavformat/utils.c (revision 18431)
+++ libavformat/utils.c (working copy)
@@ -2613,10 +2613,8 @@
     this_pktl = av_mallocz(sizeof(AVPacketList));
     this_pktl->pkt= *pkt;
-    if(pkt->destruct == av_destruct_packet)
-        pkt->destruct= NULL; // not shared -> must keep original from being freed
-    else
-        av_dup_packet(&this_pktl->pkt);  //shared -> must dup
+    pkt->destruct= NULL; // do not free original but only the copy
+    av_dup_packet(&this_pktl->pkt);  // duplicate the packet if it uses non-alloced memory
     next_point = &s->packet_buffer;

Besides being simpler, there are 3 cases, (the deprecated nofree treated the same as NULL):
1) pkt->destruct == NULL, behaviour is unchanged
2) pkt->destruct == av_destruct_packet, behaviour is unchanged since
   av_dup_packet is a nop then
3) pkt->destruct something else:
  old code:
    av_dup_packet is called but is a nop, thus destruct will later be
    called twice resulting in something equivalent to a double free
  new code:
    destruct will only be called for the copy

I not convinced that case 3) will still work completely right, but at least
this should be a step forward.

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