avformat: Add format_whitelist

This allows restricting demuxers to a list of needed ones for improved security
Note, some demuxers themselfs open other demuxers, these are only restricted if
AVOptions are forwarded to them. Please check that your code does that.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avformat.h

@@ -1584,6 +1584,22 @@ typedef struct AVFormatContext {
      */
     int format_probesize;
 
+    /**
+     * ',' seperated list of allowed decoders.
+     * If NULL then all are allowed
+     * - encoding: unused
+     * - decoding: set by user through AVOptions (NO direct access)
+     */
+    char *codec_whitelist;
+
+    /**
+     * ',' seperated list of allowed demuxers.
+     * If NULL then all are allowed
+     * - encoding: unused
+     * - decoding: set by user through AVOptions (NO direct access)
+     */
+    char *format_whitelist;
+
     /*****************************************************************
      * All fields below this line are not part of the public API. They
      * may not be used outside of libavformat and can be changed and

libavformat/options_table.h

@@ -97,6 +97,8 @@ static const AVOption avformat_options[] = {
 {"experimental", "allow non-standardized experimental variants", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_EXPERIMENTAL }, INT_MIN, INT_MAX, D|E, "strict"},
 {"max_ts_probe", "maximum number of packets to read while waiting for the first timestamp", OFFSET(max_ts_probe), AV_OPT_TYPE_INT, { .i64 = 50 }, 0, INT_MAX, D },
 {"dump_separator", "set information dump field separator", OFFSET(dump_separator), AV_OPT_TYPE_STRING, {.str = ", "}, CHAR_MIN, CHAR_MAX, D|E},
+{"codec_whitelist", "List of decoders that are allowed to be used", OFFSET(codec_whitelist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, D },
+{"format_whitelist", "List of demuxers that are allowed to be used", OFFSET(format_whitelist), AV_OPT_TYPE_STRING, { .str = NULL },  CHAR_MIN, CHAR_MAX, D },
 {NULL},
 };
 

libavformat/utils.c

@@ -291,6 +291,11 @@ static int set_codec_from_probe_data(AVFormatContext *s, AVStream *st,
 int av_demuxer_open(AVFormatContext *ic) {
     int err;
 
+    if (ic->format_whitelist && av_match_list(ic->iformat->name, ic->format_whitelist, ',') <= 0) {
+        av_log(ic, AV_LOG_ERROR, "Format not on whitelist\n");
+        return AVERROR(EINVAL);
+    }
+
     if (ic->iformat->read_header) {
         err = ic->iformat->read_header(ic);
         if (err < 0)
@@ -402,6 +407,13 @@ int avformat_open_input(AVFormatContext **ps, const char *filename,
     if ((ret = init_input(s, filename, &tmp)) < 0)
         goto fail;
     s->probe_score = ret;
+
+    if (s->format_whitelist && av_match_list(s->iformat->name, s->format_whitelist, ',') <= 0) {
+        av_log(s, AV_LOG_ERROR, "Format not on whitelist\n");
+        ret = AVERROR(EINVAL);
+        goto fail;
+    }
+
     avio_skip(s->pb, s->skip_initial_bytes);
 
     /* Check filename in case an image number is expected. */
@@ -2576,6 +2588,8 @@ static int try_decode_frame(AVFormatContext *s, AVStream *st, AVPacket *avpkt,
         /* Force thread count to 1 since the H.264 decoder will not extract
          * SPS and PPS to extradata during multi-threaded decoding. */
         av_dict_set(options ? options : &thread_opt, "threads", "1", 0);
+        if (s->codec_whitelist)
+            av_dict_set(options ? options : &thread_opt, "codec_whitelist", s->codec_whitelist, 0);
         ret = avcodec_open2(st->codec, codec, options ? options : &thread_opt);
         if (!options)
             av_dict_free(&thread_opt);
@@ -3009,6 +3023,9 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
          * SPS and PPS to extradata during multi-threaded decoding. */
         av_dict_set(options ? &options[i] : &thread_opt, "threads", "1", 0);
 
+        if (ic->codec_whitelist)
+            av_dict_set(options ? &options[i] : &thread_opt, "codec_whitelist", ic->codec_whitelist, 0);
+
         /* Ensure that subtitle_header is properly set. */
         if (st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE
             && codec && !st->codec->codec) {