Re: [FFmpeg-devel] [PATCH] avformat/hls: look for trailing GET headers with m3u8 extension check

[Leo Izen <leo.izen@gmail.com>]

On 5/14/23 05:31, Andreas Rheinhardt wrote:
> Leo Izen:
>> After commit 6b1f68ccb04d791f0250e05687c346a99ff47ea1 we refuse to use
>> URLs of the form https://foo.bar/baz.m3u8?foo=bar because it fails the
>> file extension check. This commit strips the ?foo=bar at the end before
>> checking the file extension.
>>
>> Signed-off-by: Leo Izen <leo.izen@gmail.com>
>> ---
>>   libavformat/hls.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/hls.c b/libavformat/hls.c
>> index 11e345b280..6a97cced17 100644
>> --- a/libavformat/hls.c
>> +++ b/libavformat/hls.c
>> @@ -2534,7 +2534,16 @@ static int hls_probe(const AVProbeData *p)
>>           strstr(p->buf, "#EXT-X-TARGETDURATION:") ||
>>           strstr(p->buf, "#EXT-X-MEDIA-SEQUENCE:")) {
>>   
>> -        if (!av_match_ext(p->filename, "m3u8,hls,m3u")) {
>> +        char *request_qmark = strchr(p->filename, '?');
>> +        int match_ext;
>> +
>> +        if (request_qmark)
>> +            *request_qmark = '\0';
>> +        match_ext = av_match_ext(p->filename, "m3u8,hls,m3u");
>> +        if (request_qmark)
>> +            *request_qmark = '?';
>> +
>> +        if (!match_ext) {
>>               av_log(NULL, AV_LOG_ERROR, "Not detecting m3u8/hls with non standard extension\n");
>>               return 0;
>>           }
> 
> This temporarily modifies p->filename which is a const char* (you let
> strchr cast the const away); it is provided by the user and may point to
> read-only memory, i.e. restoring the string is not safe. Furthermore, it
> may lead to data races, because the string might be used somewhere else
> concurrently (hypothetically, we could even run the probe functions in a
> multi-threaded way).
> 
> - Andreas

Would you recommend I strdup instead? I considered that but wanted to 
avoid the heap allocation.

- Leo Izen

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