[FFmpeg-cvslog] avcodec/movtextdec: Check style_start/end

[Michael Niedermayer]

ffmpeg | branch: release/2.8 | Michael Niedermayer <michael at niedermayer.cc> | Sun Apr  8 03:29:44 2018 +0200| [07cd51f10e96a4b9208d3aa99caea1068f89041b] | committer: Michael Niedermayer

avcodec/movtextdec: Check style_start/end

Limits based on 3GPP TS 26.245 V14.0.0
Fixes: Timeout
Fixes: 6377/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MOVTEXT_fuzzer-5175929115508736

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Philip Langdale <philipl at overt.org>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 249aca8f98ff7fb09c12ea68e23c862c62203b95)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=07cd51f10e96a4b9208d3aa99caea1068f89041b
---

 libavcodec/movtextdec.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libavcodec/movtextdec.c b/libavcodec/movtextdec.c
index 2f3ef7d02e..7d3dfae469 100644
--- a/libavcodec/movtextdec.c
+++ b/libavcodec/movtextdec.c
@@ -298,6 +298,14 @@ static int decode_styl(const uint8_t *tsmb, MovTextContext *m, AVPacket *avpkt)
         m->s_temp->style_start = AV_RB16(tsmb);
         tsmb += 2;
         m->s_temp->style_end = AV_RB16(tsmb);
+
+        if (   m->s_temp->style_end < m->s_temp->style_start
+            || (m->count_s && m->s_temp->style_start < m->s[m->count_s - 1]->style_end)) {
+            av_freep(&m->s_temp);
+            mov_text_cleanup(m);
+            return AVERROR(ENOMEM);
+        }
+
         tsmb += 2;
         m->s_temp->style_fontID = AV_RB16(tsmb);
         tsmb += 2;