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webm_dash_manifest_demuxer: Fix UB in cue timestamp string code and make it actually work

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Output was apparently not tested for correctness. Passing overlapping
memory to snprintf causes undefined behavior, and usually resulted in
only the very last timestamp being written to metadata, and not a list
at all.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
This commit is contained in:
Derek Buitenhuis 2017-04-20 15:02:54 +01:00
parent 41b0561dc7
commit 8e6b9ef473
1 changed files with 11 additions and 3 deletions
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14
libavformat/matroskadec.c
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@ -3823,6 +3823,7 @@ static int webm_dash_manifest_cues(AVFormatContext *s)
char *buf;
int64_t cues_start = -1, cues_end = -1, before_pos, bandwidth;
int i;
int end = 0;
// determine cues start and end positions
for (i = 0; i < seekhead_list->nb_elem; i++)
@ -3868,10 +3869,17 @@ static int webm_dash_manifest_cues(AVFormatContext *s)
if (!buf) return -1;
strcpy(buf, "");
for (i = 0; i < s->streams[0]->nb_index_entries; i++) {
snprintf(buf, (i + 1) * 20 * sizeof(char),
"%s%" PRId64, buf, s->streams[0]->index_entries[i].timestamp);
if (i != s->streams[0]->nb_index_entries - 1)
int ret = snprintf(buf + end, 20 * sizeof(char),
"%" PRId64, s->streams[0]->index_entries[i].timestamp);
if (ret <= 0 || (ret == 20 && i == s->streams[0]->nb_index_entries - 1)) {
av_log(s, AV_LOG_ERROR, "timestamp too long.\n");
return AVERROR_INVALIDDATA;
}
end += ret;
if (i != s->streams[0]->nb_index_entries - 1) {
strncat(buf, ",", sizeof(char));
end++;
}
}
av_dict_set(&s->streams[0]->metadata, CUE_TIMESTAMPS, buf, 0);
av_free(buf);