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

[Michael Niedermayer]

On Fri, Jul 12, 2019 at 08:40:40AM +0200, Olivier Maignial 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 strtoll 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 V6 --> V7:
>     - Use long long int and strtoll. LLONG_MAX is always greather than INT32_MIN while LONG_MAX can be equal to INT32_MAX. It allows to accept full INT32 range.
>     - Avoid to use errno
> 
>  libavformat/rtpdec_mpeg4.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/libavformat/rtpdec_mpeg4.c b/libavformat/rtpdec_mpeg4.c
> index 4f70599..f1cbedf 100644
> --- a/libavformat/rtpdec_mpeg4.c
> +++ b/libavformat/rtpdec_mpeg4.c
> @@ -289,15 +289,18 @@ 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;
> +                    long long int val = strtoll(value, &end_ptr, 10);
> +                    if (end_ptr == value || end_ptr[0] != '\0' ||
> +                        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;

Looking at this a bit deeper, this reads several specific values
for example sizelength which is then used to read with get_bits_long()
that is limited to 32bit. Maybe iam missing some check but if not
that is adding a bug.
I did not check what the valid range of the other cases is but
they may have similar problems

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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