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

Olivier Maignial olivier.maignial at smile.fr
Wed Jun 19 16:38:26 EEST 2019

=== 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)

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