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[FFmpeg-devel,4/8] avformat/matroskadec: Sanitize seekhead entries

Message ID 20190905201609.998-4-andreas.rheinhardt@gmail.com
State Superseded
Headers show

Commit Message

Andreas Rheinhardt Sept. 5, 2019, 8:16 p.m. UTC
A Seek element in a Matroska SeekHead should contain a SeekID and a
SeekPosition element and upon reading, they should be sanitized:

Given that IDs are restricted to 32 bit, longer SeekIDs should be treated
as invalid. Instead currently the lower 32 bits have been used.

For SeekPosition, no checks were performed for the element to be
present and if present, whether it was excessively large (i.e. the
absolute file position described by it exceeding an int64_t). The
SeekPosition element had a default value of -1 which means that a check
seems to have been intended; but it was not implemented. This commit adds
a check for overflow to the calculation of the absolute file position of
the referenced level 1 elements.
Using -1 (i.e. UINT64_MAX) as default value for SeekPosition implies that
a Seek element without SeekPosition will run afoul of this check.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
 libavformat/matroskadec.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
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diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index bdbddb58a5..2fe147126e 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -1856,8 +1856,12 @@  static void matroska_execute_seekhead(MatroskaDemuxContext *matroska)
         MatroskaSeekhead *seekheads = seekhead_list->elem;
         uint32_t id = seekheads[i].id;
         int64_t pos = seekheads[i].pos + matroska->segment_start;
+        MatroskaLevel1Element *elem;
-        MatroskaLevel1Element *elem = matroska_find_level1_elem(matroska, id);
+        if (id != seekheads[i].id || pos < matroska->segment_start)
+            continue;
+        elem = matroska_find_level1_elem(matroska, id);
         if (!elem || elem->parsed)