[FFmpeg-devel] [PATCH 1/3] avcodec/jpeg2000htdec: Check magp before using it in a shift

[Michael Niedermayer]

Fixes: shift exponent -1 is negative
Fixes: 65378/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5457678193197056

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavcodec/jpeg2000dec.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libavcodec/jpeg2000dec.c b/libavcodec/jpeg2000dec.c
index 1afc6b1e2dd..fe2afb05057 100644
--- a/libavcodec/jpeg2000dec.c
+++ b/libavcodec/jpeg2000dec.c
@@ -1910,6 +1910,8 @@ static inline void tile_codeblocks(const Jpeg2000DecoderContext *s, Jpeg2000Tile
                 int nb_precincts, precno;
                 Jpeg2000Band *band = rlevel->band + bandno;
                 int cblkno = 0, bandpos;
+                /* See Rec. ITU-T T.800, Equation E-2 */
+                int magp = quantsty->expn[subbandno] + quantsty->nguardbits - 1;
 
                 bandpos = bandno + (reslevelno > 0);
 
@@ -1917,6 +1919,9 @@ static inline void tile_codeblocks(const Jpeg2000DecoderContext *s, Jpeg2000Tile
                     band->coord[1][0] == band->coord[1][1])
                     continue;
 
+                if ((codsty->cblk_style & JPEG2000_CTSY_HTJ2K_F) && magp >= 31)
+                    return;
+
                 nb_precincts = rlevel->num_precincts_x * rlevel->num_precincts_y;
                 /* Loop on precincts */
                 for (precno = 0; precno < nb_precincts; precno++) {
@@ -1927,8 +1932,6 @@ static inline void tile_codeblocks(const Jpeg2000DecoderContext *s, Jpeg2000Tile
                          cblkno < prec->nb_codeblocks_width * prec->nb_codeblocks_height;
                          cblkno++) {
                         int x, y, ret;
-                        /* See Rec. ITU-T T.800, Equation E-2 */
-                        int magp = quantsty->expn[subbandno] + quantsty->nguardbits - 1;
 
                         Jpeg2000Cblk *cblk = prec->cblk + cblkno;
 
-- 
2.17.1