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lavc/vvc: Prevent OOB write to slice_top_left_ctu_x in PPS CBS

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Prior to the fix, in the case of a tile containing multiple slices
(pps_num_exp_slices_in_tile != 0) the number of slices was temporarily
allowed to exceed pps_num_slices_in_pic_minus1+1 and therefore
VVC_MAX_SLICES.  The number of slices was later verified, but while the
current slice index was higher than expected it was used to write to a
array of size VVC_MAX_SLICES, leading to an OOB write.

To rectify this, the patch adds some checks at an earlier stage, to
ensure that the slice index i + j at no point exceeds
pps_num_slices_in_pic_minus1.

Fixes #YWH-PGM40646-30

(cherry picked from commit 72a38c12e5)
This commit is contained in:
Frank Plowman
2025-12-29 22:14:53 +00:00
committed by Timo Rothenpieler
parent 61ac8e7d29
commit 4771d217bd
1 changed files with 13 additions and 0 deletions
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13
libavcodec/cbs_h266_syntax_template.c
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@@ -2011,6 +2011,12 @@ static int FUNC(pps) (CodedBitstreamContext *ctx, RWContext *rw,
slice_top_left_ctu_y[i] = ctu_y;
} else {
uint16_t slice_height_in_ctus;
int num_uniform_slices;
if (i + current->pps_num_exp_slices_in_tile[i] >
current->pps_num_slices_in_pic_minus1 + 1)
return AVERROR_INVALIDDATA;
for (j = 0; j < current->pps_num_exp_slices_in_tile[i];
j++) {
ues(pps_exp_slice_height_in_ctus_minus1[i][j], 0,
@@ -2031,6 +2037,13 @@ static int FUNC(pps) (CodedBitstreamContext *ctx, RWContext *rw,
uniform_slice_height = 1 +
(j == 0 ? current->row_height_val[tile_y] - 1:
current->pps_exp_slice_height_in_ctus_minus1[i][j-1]);
num_uniform_slices = (remaining_height_in_ctbs_y + uniform_slice_height - 1)
/ uniform_slice_height;
if (i + current->pps_num_exp_slices_in_tile[i] + num_uniform_slices >
current->pps_num_slices_in_pic_minus1 + 1)
return AVERROR_INVALIDDATA;
while (remaining_height_in_ctbs_y > uniform_slice_height) {
current->slice_height_in_ctus[i + j] =
uniform_slice_height;