[FFmpeg-devel] [PATCH v2 1/6] avformat/mxfenc: Never set codec_ul UID to NULL

[Andreas Rheinhardt]

mxf distinguishes codec profiles by different UIDs and therefore needs
to check that the input is actually compatible with mxf (i.e. if there
is a defined UID for it). If not, then sometimes the UID would be set to
NULL and writing the (video) packet would fail. Yet the following audio
packet would trigger writing the header (which has been postponed because
the UID is not known at the start) and if the UID is NULL, this can lead
to segfaults. This commit therefore stops setting the UID to NULL if the
input is incompatible with mxf (it has initially been set to a generic
value in mxf_write_header()).

Fixes #7993.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
---
This has already been sent earlier [1], yet it hasn't been applied
because Baptiste wanted it to be fixed by making sure that it is always
the video track that triggers writing the header. In a discussion on IRC
Tomas indicated that he wants both fixes for this bug and I will
therefore apply this here tomorrow unless there are objections.

[1]: https://ffmpeg.org/pipermail/ffmpeg-devel/2020-February/257755.html

 libavformat/mxfenc.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
index 0b399178b5..509cae8442 100644
--- a/libavformat/mxfenc.c
+++ b/libavformat/mxfenc.c
@@ -2020,7 +2020,6 @@ static int mxf_parse_prores_frame(AVFormatContext *s, AVStream *st, AVPacket *pk
     if (mxf->header_written)
         return 1;
 
-    sc->codec_ul = NULL;
     profile = st->codecpar->profile;
     for (i = 0; i < FF_ARRAY_ELEMS(mxf_prores_codec_uls); i++) {
         if (profile == mxf_prores_codec_uls[i].profile) {
@@ -2028,7 +2027,7 @@ static int mxf_parse_prores_frame(AVFormatContext *s, AVStream *st, AVPacket *pk
             break;
         }
     }
-    if (!sc->codec_ul)
+    if (i == FF_ARRAY_ELEMS(mxf_prores_codec_uls))
         return 0;
 
     sc->frame_size = pkt->size;
@@ -2074,7 +2073,6 @@ static int mxf_parse_dnxhd_frame(AVFormatContext *s, AVStream *st, AVPacket *pkt
     if (pkt->size < 43)
         return 0;
 
-    sc->codec_ul = NULL;
     cid = AV_RB32(pkt->data + 0x28);
     for (i = 0; i < FF_ARRAY_ELEMS(mxf_dnxhd_codec_uls); i++) {
         if (cid == mxf_dnxhd_codec_uls[i].cid) {
@@ -2082,7 +2080,7 @@ static int mxf_parse_dnxhd_frame(AVFormatContext *s, AVStream *st, AVPacket *pkt
             break;
         }
     }
-    if (!sc->codec_ul)
+    if (i == FF_ARRAY_ELEMS(mxf_dnxhd_codec_uls))
         return 0;
 
     sc->component_depth = 0;
@@ -2245,6 +2243,7 @@ static int mxf_parse_h264_frame(AVFormatContext *s, AVStream *st,
     const uint8_t *buf = pkt->data;
     const uint8_t *buf_end = pkt->data + pkt->size;
     const uint8_t *nal_end;
+    const UID *codec_ul = NULL;
     uint32_t state = -1;
     int extra_size = 512; // support AVC Intra files without SPS/PPS header
     int i, frame_size, slice_type, has_sps = 0, intra_only = 0, ret;
@@ -2315,12 +2314,11 @@ static int mxf_parse_h264_frame(AVFormatContext *s, AVStream *st,
 
     if (!has_sps)
         sc->interlaced = st->codecpar->field_order != AV_FIELD_PROGRESSIVE ? 1 : 0;
-    sc->codec_ul = NULL;
     frame_size = pkt->size + extra_size;
 
     for (i = 0; i < FF_ARRAY_ELEMS(mxf_h264_codec_uls); i++) {
         if (frame_size == mxf_h264_codec_uls[i].frame_size && sc->interlaced == mxf_h264_codec_uls[i].interlaced) {
-            sc->codec_ul = &mxf_h264_codec_uls[i].uid;
+            codec_ul = &mxf_h264_codec_uls[i].uid;
             sc->component_depth = 10; // AVC Intra is always 10 Bit
             sc->aspect_ratio = (AVRational){ 16, 9 }; // 16:9 is mandatory for broadcast HD
             st->codecpar->profile = mxf_h264_codec_uls[i].profile;
@@ -2334,17 +2332,18 @@ static int mxf_parse_h264_frame(AVFormatContext *s, AVStream *st,
                    mxf_h264_codec_uls[i].profile == sps->profile_idc &&
                    (mxf_h264_codec_uls[i].intra_only < 0 ||
                     mxf_h264_codec_uls[i].intra_only == intra_only)) {
-            sc->codec_ul = &mxf_h264_codec_uls[i].uid;
+            codec_ul = &mxf_h264_codec_uls[i].uid;
             st->codecpar->profile = sps->profile_idc;
             st->codecpar->level = sps->level_idc;
             // continue to check for avc intra
         }
     }
 
-    if (!sc->codec_ul) {
+    if (!codec_ul) {
         av_log(s, AV_LOG_ERROR, "h264 profile not supported\n");
         return 0;
     }
+    sc->codec_ul = codec_ul;
 
     return 1;
 }
@@ -2441,9 +2440,13 @@ static int mxf_parse_mpeg2_frame(AVFormatContext *s, AVStream *st,
             }
         }
     }
-    if (s->oformat != &ff_mxf_d10_muxer)
-        sc->codec_ul = mxf_get_mpeg2_codec_ul(st->codecpar);
-    return !!sc->codec_ul;
+    if (s->oformat != &ff_mxf_d10_muxer) {
+        const UID *codec_ul = mxf_get_mpeg2_codec_ul(st->codecpar);
+        if (!codec_ul)
+            return 0;
+        sc->codec_ul = codec_ul;
+    }
+    return 1;
 }
 
 static uint64_t mxf_parse_timestamp(int64_t timestamp64)
-- 
2.27.0