[FFmpeg-devel] [PATCH] avformat/hlsenc: Don't segfault on uncommon names

[Andreas Rheinhardt]

Andreas Rheinhardt:
> Andreas Rheinhardt:
>> The parsing process of the AVOpt-enabled string controlling the mapping
>> of input streams to variant streams is roughly as follows: Space and tab
>> separate variant stream group maps while the entries in each variant
>> stream group map are separated by ','.
>>
>> The parsing process of each variant stream group proceeded as follows:
>> At first the number of occurences of "a:", "v:" and "s:" in each variant
>> stream group is calculated so that one can can allocate an array of
>> streams with this number of entries. Then the string is split along ','
>> and each substring is parsed. If such a substring starts with "a:", "s:"
>> or "v:" it is treated as stream specifier and (if there is a correct
>> number after ':') a stream of the variant stream is mapped to one of the
>> actual input streams.
>>
>> Nothing actually guarantees that the number of streams allocated initially
>> equals the number of streams that are mapped to an actual input stream.
>> These numbers can differ if e.g. the name, the sgroup, agroup or ccgroup
>> of the variant stream contain "a:", "s:" or "v:".
>>
>> The problem hereby is that the rest of the code presumes these numbers
>> to be equal and segfaults if it isn't (because the corresponding input
>> stream is NULL).
>>
>> This commit fixes this by modifying the initial counting process to only
>> count occurences of "a:", "s:" or "v:" that are at the beginning or that
>> immediately follow a ','.
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>> ---
>> Alternatively, one could error out if these two counts differed (in
>> which case one can conclude that one of the other values must have
>> contained "a:", "s:" or "v:"). I have not done so, because using these
>> doesn't seem to be forbidden at all and there might even be usecases
>> (think of "name:The_Lord_of_the_Rings:_The_Two_Towers" or "Avengers:").
>>
>> Furthermore modifying the check has the advantage of not allocating to
>> much and it also allows to introduce keys that end with 'a', 's' or 'v'.
>>
>>  libavformat/hlsenc.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
>> index 5695c6cc95..a381ca3e9e 100644
>> --- a/libavformat/hlsenc.c
>> +++ b/libavformat/hlsenc.c
>> @@ -1951,10 +1951,13 @@ static int parse_variant_stream_mapstring(AVFormatContext *s)
>>              return AVERROR(EINVAL);
>>  
>>          q = varstr;
>> -        while (q < varstr + strlen(varstr)) {
>> +        while (1) {
>>              if (!av_strncasecmp(q, "a:", 2) || !av_strncasecmp(q, "v:", 2) ||
>>                  !av_strncasecmp(q, "s:", 2))
>>                  vs->nb_streams++;
>> +            q = strchr(q, ',');
>> +            if (!q)
>> +                break;
>>              q++;
>>          }
>>          vs->streams = av_mallocz(sizeof(AVStream *) * vs->nb_streams);
>>
> Will apply this tomorrow if there are no objections.
> 
> - Andreas
> 
Applied.

- Andreas