If the chroma components are subsampled, smaller buffers are allocated
for them. In that case the maximal block_offset for the chroma
components is not as large as for the luma component.
This fixes out of bounds writes causing segmentation faults or memory
corruption.
Signed-off-by: Andreas Cadhalpun <andreas.cadhal...@googlemail.com>
---
libavcodec/mjpegdec.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c
index cfc59ac..303b990 100644
--- a/libavcodec/mjpegdec.c
+++ b/libavcodec/mjpegdec.c
@@ -1246,7 +1246,7 @@ static int mjpeg_decode_scan(MJpegDecodeContext *s, int
nb_components, int Ah,
int mb_bitmask_size,
const AVFrame *reference)
{
- int i, mb_x, mb_y;
+ int i, mb_x, mb_y, chroma_h_shift, chroma_v_shift;
uint8_t *data[MAX_COMPONENTS];
const uint8_t *reference_data[MAX_COMPONENTS];
int linesize[MAX_COMPONENTS];
@@ -1271,6 +1271,9 @@ static int mjpeg_decode_scan(MJpegDecodeContext *s, int
nb_components, int Ah,
s->coefs_finished[c] |= 1;
}
+ av_pix_fmt_get_chroma_sub_sample(s->avctx->pix_fmt, &chroma_h_shift,
+ &chroma_v_shift);
+
for (mb_y = 0; mb_y < s->mb_height; mb_y++) {
for (mb_x = 0; mb_x < s->mb_width; mb_x++) {
const int copy_mb = mb_bitmask && !get_bits1(&mb_bitmask_gb);
@@ -1285,7 +1288,7 @@ static int mjpeg_decode_scan(MJpegDecodeContext *s, int
nb_components, int Ah,
}
for (i = 0; i < nb_components; i++) {
uint8_t *ptr;
- int n, h, v, x, y, c, j;
+ int n, h, v, x, y, c, j, h_shift, v_shift;
int block_offset;
n = s->nb_blocks[i];
c = s->comp_index[i];
@@ -1293,14 +1296,16 @@ static int mjpeg_decode_scan(MJpegDecodeContext *s, int
nb_components, int Ah,
v = s->v_scount[i];
x = 0;
y = 0;
+ h_shift = c ? chroma_h_shift: 0;
+ v_shift = c ? chroma_v_shift: 0;
for (j = 0; j < n; j++) {
block_offset = (((linesize[c] * (v * mb_y + y) * 8) +
(h * mb_x + x) * 8 * bytes_per_pixel) >>
s->avctx->lowres);
if (s->interlaced && s->bottom_field)
block_offset += linesize[c] >> 1;
- if ( 8*(h * mb_x + x) < s->width
- && 8*(v * mb_y + y) < s->height) {
+ if ( 8*(h * mb_x + x) < (s->width + (1 << h_shift) - 1)
>> h_shift
+ && 8*(v * mb_y + y) < (s->height + (1 << v_shift) - 1)
>> v_shift) {
ptr = data[c] + block_offset;
} else
ptr = NULL;
--
2.6.2
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