[FFmpeg-devel] [PATCH v6] Fix integer parameters size check in SDP fmtp line

[Reimar Döffinger]

I don't think we should be using errno when avoidable, and it is avoidable here by disallowing min/max int32 values themselves. Or using strtoll.
I'm also rather sceptical about allowing negative values here, does that make sense?
Admittedly the type is set to just "int", but maybe it should be unsigned instead?

On 28.06.2019, at 08:46, Olivier MAIGNIAL <olivier.maignial at smile.fr> wrote:

> Hello here!
> 
> A simple ping about this patch
> If you have any question, feel free to ask!
> 
> Regards,
> Olivier
> 
> On Wed, Jun 19, 2019 at 3:38 PM Olivier Maignial <olivier.maignial at smile.fr>
> wrote:
> 
>> === PROBLEM ===
>> 
>> I was trying to record h264 + aac streams from an RTSP server to mp4 file.
>> using this command line:
>>    ffmpeg -v verbose -y -i "rtsp://<ip>/my_resources" -codec copy -bsf:a
>> aac_adtstoasc test.mp4
>> 
>> FFmpeg then fail to record audio and output this logs:
>>    [rtsp @ 0xcda1f0] The profile-level-id field size is invalid (40)
>>    [rtsp @ 0xcda1f0] Error parsing AU headers
>>    ...
>>    [rtsp @ 0xcda1f0] Could not find codec parameters for stream 1 (Audio:
>> aac, 48000 Hz, 1 channels): unspecified sample format
>> 
>> In SDP provided by my RTSP server I had this fmtp line:
>>    a=fmtp:98 streamType=5; profile-level-id=40; mode=AAC-hbr;
>> config=1188; sizeLength=13; indexLength=3; indexDeltaLength=3;
>> 
>> In FFmpeg code, I found a check introduced by commit
>> 24130234cd9dd733116d17b724ea4c8e12ce097a. It disallows values greater than
>> 32 for fmtp line parameters.
>> However, In RFC-6416 (RTP Payload Format for MPEG-4 Audio/Visual Streams)
>> give examples of "profile-level-id" values for AAC, up to 55.
>> Furthermore, RFC-4566 (SDP: Session Description Protocol) do not give any
>> limit of size on interger parameters given in fmtp line.
>> 
>> === FIX ===
>> 
>> Instead of prohibit values over 32, I propose to check the possible
>> integer overflow.
>> The use of strtol allow to check the string validity and the possible
>> overflow.
>> Value is then checked against INT32_MIN and INT32_MAX. Using INT32_MIN/MAX
>> ensure to have the same behavior on 32 or 64 bits platforms.
>> 
>> This patch fix my problem and I now can record my RTSP AAC stream to mp4.
>> It has passed the full fate tests suite sucessfully.
>> 
>> Signed-off-by: Olivier Maignial <olivier.maignial at smile.fr>
>> ---
>> 
>> Changes V5 -> V6:
>>    - Simplify code
>> 
>> libavformat/rtpdec_mpeg4.c | 15 ++++++++++-----
>> 1 file changed, 10 insertions(+), 5 deletions(-)
>> 
>> diff --git a/libavformat/rtpdec_mpeg4.c b/libavformat/rtpdec_mpeg4.c
>> index 4f70599..9c4f8a1 100644
>> --- a/libavformat/rtpdec_mpeg4.c
>> +++ b/libavformat/rtpdec_mpeg4.c
>> @@ -289,15 +289,20 @@ static int parse_fmtp(AVFormatContext *s,
>>         for (i = 0; attr_names[i].str; ++i) {
>>             if (!av_strcasecmp(attr, attr_names[i].str)) {
>>                 if (attr_names[i].type == ATTR_NAME_TYPE_INT) {
>> -                    int val = atoi(value);
>> -                    if (val > 32) {
>> +                    char *end_ptr = NULL;
>> +                    errno = 0;
>> +                    long int val = strtol(value, &end_ptr, 10);
>> +                    if (end_ptr == value || end_ptr[0] != '\0' ||
>> +                        errno == ERANGE ||
>> +                        val < INT32_MIN || val > INT32_MAX) {
>>                         av_log(s, AV_LOG_ERROR,
>> -                               "The %s field size is invalid (%d)\n",
>> -                               attr, val);
>> +                               "The %s field value is not a valid number,
>> or overflows int32: %s\n",
>> +                               attr, value);
>>                         return AVERROR_INVALIDDATA;
>>                     }
>> +
>>                     *(int *)((char *)data+
>> -                        attr_names[i].offset) = val;
>> +                        attr_names[i].offset) = (int) val;
>>                 } else if (attr_names[i].type == ATTR_NAME_TYPE_STR) {
>>                     char *val = av_strdup(value);
>>                     if (!val)
>> --
>> 2.7.4
>> 
>> 
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