On 5/16/2019 7:29 PM, Andreas Rheinhardt wrote:
> ebml_read_num had a number of flaws:
>
> 1. The check for read errors/EOF was totally wrong. E.g. an EBML number
> beginning with the invalid 0x00 would be considered a read error,
> although it is just invalid data.
> 2. The check for read errors/EOF was done just once, after reading the
> first byte of the EBML number. But errors/EOF can happen inbetween, of
> course, and this wasn't checked.
> 3. There was no way to distinguish when EOF should be an error (because
> the data has to be there) for which an error message should be emitted
> and when it is not necessarily an error (namely during parsing of EBML
> IDs). Such a possibility has been added and used.
>
> All this was fixed; furthermore, the error messages for invalid EBML
> numbers were improved and useless initializations were removed.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
> ---
> libavformat/matroskadec.c | 76 +++++++++++++++++++++++----------------
> 1 file changed, 45 insertions(+), 31 deletions(-)
>
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index 0f7decb212..431e742a2d 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -820,33 +820,30 @@ static int ebml_level_end(MatroskaDemuxContext
> *matroska)
> * Returns: number of bytes read, < 0 on error
> */
> static int ebml_read_num(MatroskaDemuxContext *matroska, AVIOContext *pb,
> - int max_size, uint64_t *number)
> + int max_size, uint64_t *number, int eof_forbidden)
> {
> - int read = 1, n = 1;
> - uint64_t total = 0;
> + int read, n = 1;
> + uint64_t total;
> + int64_t pos;
>
> - /* The first byte tells us the length in bytes - avio_r8() can normally
> - * return 0, but since that's not a valid first ebmlID byte, we can
> - * use it safely here to catch EOS. */
> - if (!(total = avio_r8(pb))) {
> - /* we might encounter EOS here */
> - if (!avio_feof(pb)) {
> - int64_t pos = avio_tell(pb);
> - av_log(matroska->ctx, AV_LOG_ERROR,
> - "Read error at pos. %"PRIu64" (0x%"PRIx64")\n",
> - pos, pos);
> - return pb->error ? pb->error : AVERROR(EIO);
> - }
> - return AVERROR_EOF;
> - }
> + /* The first byte tells us the length in bytes - except when it is zero.
> */
> + total = avio_r8(pb);
> + if (pb->eof_reached)
> + goto err;
>
> /* get the length of the EBML number */
> - read = 8 - ff_log2_tab[total];
> - if (read > max_size) {
> - int64_t pos = avio_tell(pb) - 1;
> - av_log(matroska->ctx, AV_LOG_ERROR,
> - "Invalid EBML number size tag 0x%02x at pos %"PRIu64"
> (0x%"PRIx64")\n",
> - (uint8_t) total, pos, pos);
> + if (!total || (read = 8 - ff_log2_tab[total]) > max_size) {
> + pos = avio_tell(pb) - 1;
> + if (!total) {
> + av_log(matroska->ctx, AV_LOG_ERROR,
> + "0x00 at pos %"PRId64" (0x%"PRIx64") invalid as first
> byte "
> + "of an EBML number\n", pos, pos);
> + } else {
> + av_log(matroska->ctx, AV_LOG_ERROR,
> + "Length %d indicated by an EBML number's first byte
> 0x%02x "
> + "at pos %"PRId64" (0x%"PRIx64") exceeds max length %d.\n",
> + read, (uint8_t) total, pos, pos, max_size);
> + }
> return AVERROR_INVALIDDATA;
> }
>
> @@ -855,9 +852,27 @@ static int ebml_read_num(MatroskaDemuxContext *matroska,
> AVIOContext *pb,
> while (n++ < read)
> total = (total << 8) | avio_r8(pb);
>
> + if (pb->eof_reached) {
> + eof_forbidden = 1;
> + goto err;
> + }
> +
> *number = total;
>
> return read;
> +
> +err:
> + pos = avio_tell(pb);
> + if (pb->error) {
> + av_log(matroska->ctx, AV_LOG_ERROR,
> + "Read error at pos. %"PRIu64" (0x%"PRIx64")\n",
> + pos, pos);
> + return pb->error;
> + }
> + if (eof_forbidden)
> + av_log(matroska->ctx, AV_LOG_ERROR, "File ended prematurely "
> + "at pos. %"PRIu64" (0x%"PRIx64")\n", pos, pos);
> + return AVERROR_EOF;
Same here, return EIO when the file ends unexpectedly and you want to
make sure libavformat knows demuxing failed.
> }
>
> /**
> @@ -868,7 +883,7 @@ static int ebml_read_num(MatroskaDemuxContext *matroska,
> AVIOContext *pb,
> static int ebml_read_length(MatroskaDemuxContext *matroska, AVIOContext *pb,
> uint64_t *number)
> {
> - int res = ebml_read_num(matroska, pb, 8, number);
> + int res = ebml_read_num(matroska, pb, 8, number, 1);
> if (res > 0 && *number + 1 == 1ULL << (7 * res))
> *number = EBML_UNKNOWN_LENGTH;
> return res;
> @@ -1010,7 +1025,7 @@ static int matroska_ebmlnum_uint(MatroskaDemuxContext
> *matroska,
> {
> AVIOContext pb;
> ffio_init_context(&pb, data, size, 0, NULL, NULL, NULL, NULL);
> - return ebml_read_num(matroska, &pb, FFMIN(size, 8), num);
> + return ebml_read_num(matroska, &pb, FFMIN(size, 8), num, 1);
> }
>
> /*
> @@ -1057,7 +1072,7 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
> EbmlSyntax *syntax,
> {
> if (!matroska->current_id) {
> uint64_t id;
> - int res = ebml_read_num(matroska, matroska->ctx->pb, 4, &id);
> + int res = ebml_read_num(matroska, matroska->ctx->pb, 4, &id, 0);
> if (res < 0) {
> // in live mode, finish parsing if EOF is reached.
> return (matroska->is_live && matroska->ctx->pb->eof_reached &&
> @@ -3353,10 +3368,9 @@ static int matroska_parse_block(MatroskaDemuxContext
> *matroska, AVBufferRef *buf
> uint64_t num;
> int trust_default_duration = 1;
>
> - if ((n = matroska_ebmlnum_uint(matroska, data, size, &num)) < 0) {
> - av_log(matroska->ctx, AV_LOG_ERROR, "EBML block data error\n");
> + if ((n = matroska_ebmlnum_uint(matroska, data, size, &num)) < 0)
> return n;
> - }
> +
> data += n;
> size -= n;
>
> @@ -3717,7 +3731,7 @@ static int
> webm_clusters_start_with_keyframe(AVFormatContext *s)
> AVPacket *pkt;
> avio_seek(s->pb, cluster_pos, SEEK_SET);
> // read cluster id and length
> - read = ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id);
> + read = ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id, 1);
> if (read < 0 || cluster_id != 0xF43B675) // done with all clusters
> break;
> read = ebml_read_length(matroska, matroska->ctx->pb,
> &cluster_length);
> @@ -3935,7 +3949,7 @@ static int webm_dash_manifest_cues(AVFormatContext *s,
> int64_t init_range)
> // cues_end is inclusive and the above sum is reduced by 1.
> uint64_t cues_length, cues_id;
> int bytes_read;
> - bytes_read = ebml_read_num (matroska, matroska->ctx->pb, 4,
> &cues_id);
> + bytes_read = ebml_read_num (matroska, matroska->ctx->pb, 4,
> &cues_id, 1);
> if (bytes_read < 0 || cues_id != (MATROSKA_ID_CUES & 0xfffffff))
> return bytes_read < 0 ? bytes_read : AVERROR_INVALIDDATA;
> bytes_read = ebml_read_length(matroska, matroska->ctx->pb,
> &cues_length);
>
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