[vlc-devel] Crash while seeking a Matroska file (Ticket #1006 et all) -fix

[Harry Sintonen]

   Hello!

I've tracked down the MKV seek crash to modules/demux/mkv.cpp
void matroska_segment_c::Seek( mtime_t i_date, mtime_t i_time_offset )

The 'while( i_track_skipping > 0 )' -loop does BlockGet() to get the 
'block'. However for LIBMATROSKA_VERSION >= 0x000800 it can happen that 
the 'block' is NULL, resulting in NULL references later in the loop:

             if( tracks[i_track]->i_number == block->TrackNum() )

and:

         sys.i_pts = (sys.i_chapter_time + block->GlobalTimecode()) / (mtime_t) 1000;

I've included a proposed fix as an attachment (I bet those long lines
would barf).

In case the attachment is stripped down, it's temporarily here aswell:
http://www.iki.fi/sintonen/temp/mkv.cpp.diff.txt


   Regards,
-- 
l=2001;main(i){float o,O,_,I,D;for(;O=I=l/571.-1.75,l;)for(putchar(--l%80?
i:10),o=D=l%80*.05-2,i=31;_=O*O,O=2*o*O+I,o=o*o-_+D,o+_+_<4+D&i++<87;);puts
("  Harry 'Piru' Sintonen <sintonen at iki.fi> http://www.iki.fi/sintonen");}
-------------- next part --------------
--- mkv.cpp.old	Wed May  9 04:14:29 2007
+++ mkv.cpp	Wed May  9 04:16:45 2007
@@ -5672,14 +5672,24 @@
         ep->Down();
 
         for( i_track = 0; i_track < tracks.size(); i_track++ )
         {
+#if LIBMATROSKA_VERSION >= 0x000800
+            if( (simpleblock != NULL && tracks[i_track]->i_number == simpleblock->TrackNum()) ||
+                (block != NULL && tracks[i_track]->i_number == block->TrackNum()) )
+#else
             if( tracks[i_track]->i_number == block->TrackNum() )
+#endif
             {
                 break;
             }
         }
 
+#if LIBMATROSKA_VERSION >= 0x000800
+        if( simpleblock )
+            sys.i_pts = (sys.i_chapter_time + simpleblock->GlobalTimecode()) / (mtime_t) 1000;
+        else
+#endif
         sys.i_pts = (sys.i_chapter_time + block->GlobalTimecode()) / (mtime_t) 1000;
 
         if( i_track < tracks.size() )
         {