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From: Frank Plowman <post@frankplowman.com>
To: ffmpeg-devel@ffmpeg.org
Date: Fri, 18 Apr 2025 15:38:45 +0100
Message-ID: <20250418143949.24285-1-post@frankplowman.com>
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Subject: [FFmpeg-devel] [PATCH] lavc/vvc: Detect subpic overlaps at CTU level
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Cc: Frank Plowman <post@frankplowman.com>, nuomi2021@gmail.com
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In d5dbcc00d889fb17948b025a468b00ddbea9e058, it was hoped that detection
of subpicture overlaps could be performed at the tile level, so as to
avoid introducing per-CTU checks. Unfortunately since that patch,
fuzzing has indicated there are some structures involving
pps_subpic_one_or_more_tiles_slice where tile-level checking is not
sufficient. Performing the check at the CTU level should (touch wood)
be the be-all and and-all of this, as CTUs are the lowest common
denominator of the picture partitioning.
Signed-off-by: Frank Plowman <post@frankplowman.com>
---
libavcodec/vvc/ps.c | 81 +++++++++++++++++++++++----------------------
1 file changed, 42 insertions(+), 39 deletions(-)
diff --git a/libavcodec/vvc/ps.c b/libavcodec/vvc/ps.c
index e8c312d8ac..4edfe408c0 100644
--- a/libavcodec/vvc/ps.c
+++ b/libavcodec/vvc/ps.c
@@ -402,14 +402,35 @@ static int ctu_rs(const int rx, const int ry, const VVCPPS *pps)
return pps->ctb_width * ry + rx;
}
+static void pps_add_ctu(VVCPPS *pps, int *off, const int x, const int y)
+{
+ pps->ctb_addr_in_slice[*off] = ctu_rs(x, y, pps);
+ (*off)++;
+}
+
static int pps_add_ctus(VVCPPS *pps, int *off, const int rx, const int ry,
const int w, const int h)
{
int start = *off;
for (int y = 0; y < h; y++) {
for (int x = 0; x < w; x++) {
- pps->ctb_addr_in_slice[*off] = ctu_rs(rx + x, ry + y, pps);
- (*off)++;
+ pps_add_ctu(pps, off, rx + x, ry + y);
+ }
+ }
+ return *off - start;
+}
+
+// Similar to pps_add_ctus, but with a check to ensure a given CTU isn't used
+// multiple times, to be used with some of the more complex partitioning mechanisms.
+static int pps_add_ctus_check(VVCPPS *pps, int *off, const int rx, const int ry,
+ const int w, const int h)
+{
+ int start = *off;
+ for (int y = 0; y < h; y++) {
+ for (int x = 0; x < w; x++) {
+ if (*off >= pps->ctb_count)
+ return AVERROR_INVALIDDATA;
+ pps_add_ctu(pps, off, rx + x, ry + y);
}
}
return *off - start;
@@ -451,50 +472,39 @@ static void subpic_tiles(int *tile_x, int *tile_y, int *tile_x_end, int *tile_y_
(*tile_y_end)++;
}
-static bool mark_tile_as_used(bool *tile_in_subpic, const int tx, const int ty, const int tile_columns)
-{
- const size_t tile_idx = ty * tile_columns + tx;
- if (tile_in_subpic[tile_idx]) {
- /* the tile is covered by other subpictures */
- return false;
- }
- tile_in_subpic[tile_idx] = true;
- return true;
-}
-
-static int pps_subpic_less_than_one_tile_slice(VVCPPS *pps, const VVCSPS *sps, const int i, const int tx, const int ty, int *off, bool *tile_in_subpic)
+static int pps_subpic_less_than_one_tile_slice(VVCPPS *pps, const VVCSPS *sps, const int i, const int tx, const int ty, int *off)
{
- const int subpic_bottom = sps->r->sps_subpic_ctu_top_left_y[i] + sps->r->sps_subpic_height_minus1[i];
- const int tile_bottom = pps->row_bd[ty] + pps->r->row_height_val[ty] - 1;
- const bool is_final_subpic_in_tile = subpic_bottom == tile_bottom;
-
- if (is_final_subpic_in_tile && !mark_tile_as_used(tile_in_subpic, tx, ty, pps->r->num_tile_columns))
- return AVERROR_INVALIDDATA;
-
- pps->num_ctus_in_slice[i] = pps_add_ctus(pps, off,
+ const int ret = pps_add_ctus_check(pps, off,
sps->r->sps_subpic_ctu_top_left_x[i], sps->r->sps_subpic_ctu_top_left_y[i],
sps->r->sps_subpic_width_minus1[i] + 1, sps->r->sps_subpic_height_minus1[i] + 1);
- return 0;
+ if (ret < 0)
+ return ret;
+ else {
+ pps->num_ctus_in_slice[i] = ret;
+ return 0;
+ }
}
static int pps_subpic_one_or_more_tiles_slice(VVCPPS *pps, const int tile_x, const int tile_y, const int x_end, const int y_end,
- const int i, int *off, bool *tile_in_subpic)
+ const int i, int *off)
{
for (int ty = tile_y; ty < y_end; ty++) {
for (int tx = tile_x; tx < x_end; tx++) {
- if (!mark_tile_as_used(tile_in_subpic, tx, ty, pps->r->num_tile_columns))
- return AVERROR_INVALIDDATA;
-
- pps->num_ctus_in_slice[i] += pps_add_ctus(pps, off,
+ const int ret = pps_add_ctus_check(pps, off,
pps->col_bd[tx], pps->row_bd[ty],
pps->r->col_width_val[tx], pps->r->row_height_val[ty]);
+
+ if (ret < 0)
+ return ret;
+ else
+ pps->num_ctus_in_slice[i] += ret;
}
}
return 0;
}
-static int pps_subpic_slice(VVCPPS *pps, const VVCSPS *sps, const int i, int *off, bool *tile_in_subpic)
+static int pps_subpic_slice(VVCPPS *pps, const VVCSPS *sps, const int i, int *off)
{
int tx, ty, x_end, y_end;
@@ -503,9 +513,9 @@ static int pps_subpic_slice(VVCPPS *pps, const VVCSPS *sps, const int i, int *of
subpic_tiles(&tx, &ty, &x_end, &y_end, sps, pps, i);
if (ty + 1 == y_end && sps->r->sps_subpic_height_minus1[i] + 1 < pps->r->row_height_val[ty])
- return pps_subpic_less_than_one_tile_slice(pps, sps, i, tx, ty, off, tile_in_subpic);
+ return pps_subpic_less_than_one_tile_slice(pps, sps, i, tx, ty, off);
else
- return pps_subpic_one_or_more_tiles_slice(pps, tx, ty, x_end, y_end, i, off, tile_in_subpic);
+ return pps_subpic_one_or_more_tiles_slice(pps, tx, ty, x_end, y_end, i, off);
}
static int pps_single_slice_per_subpic(VVCPPS *pps, const VVCSPS *sps, int *off)
@@ -513,18 +523,11 @@ static int pps_single_slice_per_subpic(VVCPPS *pps, const VVCSPS *sps, int *off)
if (!sps->r->sps_subpic_info_present_flag) {
pps_single_slice_picture(pps, off);
} else {
- bool tile_in_subpic[VVC_MAX_TILES_PER_AU] = {0};
for (int i = 0; i < pps->r->pps_num_slices_in_pic_minus1 + 1; i++) {
- const int ret = pps_subpic_slice(pps, sps, i, off, tile_in_subpic);
+ const int ret = pps_subpic_slice(pps, sps, i, off);
if (ret < 0)
return ret;
}
-
- // We only use tile_in_subpic to check that the subpictures don't overlap
- // here; we don't use tile_in_subpic to check that the subpictures cover
- // every tile. It is possible to avoid doing this work here because the
- // covering property of subpictures is already guaranteed by the mechanisms
- // which check every CTU belongs to a slice.
}
return 0;
}
--
2.47.0
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