Commit 1249698e1b424cff8e77e6a83cfdbc9d11e01aa7 made ff_mjpeg_decode_dht() call build_vlc() with a wrong (too hight) number of codes. The reason it worked is that the lengths of the extraneous entries is initialized to zero and ff_init_vlc_sparse() ignores codes with a length of zero. But using a too high number of codes was nevertheless bad, because a) the assert in build_vlc() could have been triggered (namely if the real amount of codes is 256) and b) the loop in build_vlc() uses initialized data (leading to Valgrind errors [1]). Furthermore, the old code spend CPU cycles in said loop although the result won't be used anyway.
[1]: http://fate.ffmpeg.org/report.cgi?slot=x86_64-archlinux-gcc-valgrind&time=20201008025137 Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com> --- libavcodec/mjpegdec.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c index 44bbae010c..4128c47303 100644 --- a/libavcodec/mjpegdec.c +++ b/libavcodec/mjpegdec.c @@ -78,7 +78,7 @@ static int build_vlc(VLC *vlc, const uint8_t *bits_table, build_huffman_codes(huff_size, huff_code, bits_table); - for (i = 0; i < 256; i++) { + for (i = 0; i < nb_codes; i++) { huff_sym[i] = val_table[i] + 16 * is_ac; if (is_ac && !val_table[i]) @@ -295,15 +295,15 @@ int ff_mjpeg_decode_dht(MJpegDecodeContext *s) /* build VLC and flush previous vlc if present */ ff_free_vlc(&s->vlcs[class][index]); av_log(s->avctx, AV_LOG_DEBUG, "class=%d index=%d nb_codes=%d\n", - class, index, n + 1); + class, index, n); if ((ret = build_vlc(&s->vlcs[class][index], bits_table, val_table, - n + 1, 0, class > 0)) < 0) + n, 0, class > 0)) < 0) return ret; if (class > 0) { ff_free_vlc(&s->vlcs[2][index]); if ((ret = build_vlc(&s->vlcs[2][index], bits_table, val_table, - n + 1, 0, 0)) < 0) + n, 0, 0)) < 0) return ret; } -- 2.25.1 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
