ffmpeg | branch: master | Mark Thompson <s...@jkqxz.net> | Sun Oct 22 19:35:52 2023 +0100| [7110a36ba07f85ca2996d3b99898a4819e72d9bb] | committer: Michael Niedermayer
cbs_av1: Reject thirty-two zero bits in uvlc code The spec allows at least thirty-two zero bits followed by a one to mean 2^32-1, with no constraint on the number of zeroes. The libaom reference decoder does not match this, instead reading thirty-two zeroes but not the following one to mean 2^32-1. These two interpretations are incompatible and other implementations may follow one or the other. Therefore reject thirty-two zeroes because the intended behaviour is not clear. Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=7110a36ba07f85ca2996d3b99898a4819e72d9bb --- libavcodec/cbs_av1.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/libavcodec/cbs_av1.c b/libavcodec/cbs_av1.c index fb82996022..458381f038 100644 --- a/libavcodec/cbs_av1.c +++ b/libavcodec/cbs_av1.c @@ -36,7 +36,7 @@ static int cbs_av1_read_uvlc(CodedBitstreamContext *ctx, GetBitContext *gbc, CBS_TRACE_READ_START(); zeroes = 0; - while (1) { + while (zeroes < 32) { if (get_bits_left(gbc) < 1) { av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid uvlc code at " "%s: bitstream ended.\n", name); @@ -49,10 +49,18 @@ static int cbs_av1_read_uvlc(CodedBitstreamContext *ctx, GetBitContext *gbc, } if (zeroes >= 32) { - // Note that the spec allows an arbitrarily large number of - // zero bits followed by a one bit in this case, but the - // libaom implementation does not support it. - value = MAX_UINT_BITS(32); + // The spec allows at least thirty-two zero bits followed by a + // one to mean 2^32-1, with no constraint on the number of + // zeroes. The libaom reference decoder does not match this, + // instead reading thirty-two zeroes but not the following one + // to mean 2^32-1. These two interpretations are incompatible + // and other implementations may follow one or the other. + // Therefore we reject thirty-two zeroes because the intended + // behaviour is not clear. + av_log(ctx->log_ctx, AV_LOG_ERROR, "Thirty-two zero bits in " + "%s uvlc code: considered invalid due to conflicting " + "standard and reference decoder behaviour.\n", name); + return AVERROR_INVALIDDATA; } else { if (get_bits_left(gbc) < zeroes) { av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid uvlc code at " _______________________________________________ ffmpeg-cvslog mailing list ffmpeg-cvslog@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-cvslog To unsubscribe, visit link above, or email ffmpeg-cvslog-requ...@ffmpeg.org with subject "unsubscribe".
