[FFmpeg-cvslog] rm: prevent infinite loops for index parsing.

[Ronald S. Bultje]

ffmpeg | branch: release/0.8 | Ronald S. Bultje <rsbultje at gmail.com> | Wed Feb 22 11:33:24 2012 -0800| [811989e91092bfa8cbcf6305eee7c1353da99809] | committer: Reinhard Tartler

rm: prevent infinite loops for index parsing.

Specifically, prevent jumping back in the file for the next index, since
this can lead to infinite loops where we jump between indexes referring
to each other, and don't read indexes that don't fit in the file.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable at libav.org
(cherry picked from commit aac07a7a4c2c7a4a29cf6dbc88c1b9fdd191b99d)

Signed-off-by: Reinhard Tartler <siretart at tauware.de>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=811989e91092bfa8cbcf6305eee7c1353da99809
---

 libavformat/rmdec.c |   20 +++++++++++++++++---
 1 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/libavformat/rmdec.c b/libavformat/rmdec.c
index fbc4d0c..dbfeb92 100644
--- a/libavformat/rmdec.c
+++ b/libavformat/rmdec.c
@@ -350,8 +350,19 @@ static int rm_read_index(AVFormatContext *s)
                 st = s->streams[n];
                 break;
             }
-        if (n == s->nb_streams)
+        if (n == s->nb_streams) {
+            av_log(s, AV_LOG_ERROR,
+                   "Invalid stream index %d for index at pos %"PRId64"\n",
+                   str_id, avio_tell(pb));
             goto skip;
+        } else if ((avio_size(pb) - avio_tell(pb)) / 14 < n_pkts) {
+            av_log(s, AV_LOG_ERROR,
+                   "Nr. of packets in packet index for stream index %d "
+                   "exceeds filesize (%"PRId64" at %"PRId64" = %d)\n",
+                   str_id, avio_size(pb), avio_tell(pb),
+                   (avio_size(pb) - avio_tell(pb)) / 14);
+            goto skip;
+        }
 
         for (n = 0; n < n_pkts; n++) {
             avio_skip(pb, 2);
@@ -363,9 +374,12 @@ static int rm_read_index(AVFormatContext *s)
         }
 
 skip:
-        if (next_off && avio_tell(pb) != next_off &&
-            avio_seek(pb, next_off, SEEK_SET) < 0)
+        if (next_off && avio_tell(pb) < next_off &&
+            avio_seek(pb, next_off, SEEK_SET) < 0) {
+            av_log(s, AV_LOG_ERROR,
+                   "Non-linear index detected, not supported\n");
             return -1;
+        }
     } while (next_off);
 
     return 0;