[FFmpeg-devel] [PATCH] lavc/vvc: Add max parameter to kth_order_egk_decode

[Frank Plowman <post@frankplowman.com>]

Prior to this patch, kth_order_egk_decode could read arbitrarily
large values which then overflowed and caused various issues.
Patch fixes this by making kth_order_egk_decode falliable,
requiring the caller to specify an upper bound and returning an
error if the read value would exceed that bound.

This patch resolves the same issue as
eb52251c0ab025b6b40b28994bc9dc616813b190, but I think this is the proper
fix as it also addresses issues with syntax elements besides
ff_vvc_num_signalled_palette_entries.

Patch also includes a minor fix in hls_palette_coding, where the
error code returned by palette_subblock_data was previously unchecked.

Signed-off-by: Frank Plowman <post@frankplowman.com>
---
I would appreciate a second pair of eyes on my changes to
kth_order_egk_decode, particularly wrt the behaviour concerning
potential overflows.  My understanding when writing this was that
overflows can only potentially occur when reading the prefix, hence the
per-prefix bit check there.  Then for the suffix no overflow can occur
so we just check the final value.
---
 libavcodec/vvc/cabac.c | 27 ++++++++++++++++-----------
 libavcodec/vvc/cabac.h |  6 +++---
 libavcodec/vvc/ctu.c   | 39 +++++++++++++++++++++++++--------------
 3 files changed, 44 insertions(+), 28 deletions(-)

diff --git a/libavcodec/vvc/cabac.c b/libavcodec/vvc/cabac.c
index 6847ce59af..e0cc82c3e1 100644
--- a/libavcodec/vvc/cabac.c
+++ b/libavcodec/vvc/cabac.c
@@ -929,24 +929,29 @@ static int truncated_binary_decode(VVCLocalContext *lc, const int c_max)
 }
 
 // 9.3.3.5 k-th order Exp - Golomb binarization process
-static int kth_order_egk_decode(CABACContext *c, int k)
+static int kth_order_egk_decode(CABACContext *c, int *value, int k, const int max)
 {
     int bit    = 1;
-    int value  = 0;
     int symbol = 0;
+    *value     = 0;
 
     while (bit) {
         bit = get_cabac_bypass(c);
-        value += bit << k++;
+        if (max - *value < (bit << k))
+            return AVERROR_INVALIDDATA;
+        *value += bit << k++;
     }
 
     if (--k) {
         for (int i = 0; i < k; i++)
             symbol = (symbol << 1) | get_cabac_bypass(c);
-        value += symbol;
+        *value += symbol;
     }
 
-    return value;
+    if (*value > max)
+        return AVERROR_INVALIDDATA;
+
+    return 0;
 }
 
 // 9.3.3.6 Limited k-th order Exp-Golomb binarization process
@@ -1377,14 +1382,14 @@ int ff_vvc_intra_chroma_pred_mode(VVCLocalContext *lc)
     return (get_cabac_bypass(&lc->ep->cc) << 1) | get_cabac_bypass(&lc->ep->cc);
 }
 
-int ff_vvc_palette_predictor_run(VVCLocalContext *lc)
+int ff_vvc_palette_predictor_run(VVCLocalContext *lc, int *value, const int max)
 {
-    return kth_order_egk_decode(&lc->ep->cc, 0);
+    return kth_order_egk_decode(&lc->ep->cc, value, 0, max);
 }
 
-int ff_vvc_num_signalled_palette_entries(VVCLocalContext *lc)
+int ff_vvc_num_signalled_palette_entries(VVCLocalContext *lc, int *value, const int max)
 {
-    return kth_order_egk_decode(&lc->ep->cc, 0);
+    return kth_order_egk_decode(&lc->ep->cc, value, 0, max);
 }
 
 int ff_vvc_new_palette_entries(VVCLocalContext *lc, const int bit_depth)
@@ -1424,9 +1429,9 @@ int ff_vvc_palette_idx_idc(VVCLocalContext *lc, const int max_palette_index, con
     return truncated_binary_decode(lc, max_palette_index - adjust);
 }
 
-int ff_vvc_palette_escape_val(VVCLocalContext *lc)
+int ff_vvc_palette_escape_val(VVCLocalContext *lc, int *value, const int max)
 {
-    return kth_order_egk_decode(&lc->ep->cc, 5);
+    return kth_order_egk_decode(&lc->ep->cc, value, 5, max);
 }
 
 int ff_vvc_general_merge_flag(VVCLocalContext *lc)
diff --git a/libavcodec/vvc/cabac.h b/libavcodec/vvc/cabac.h
index 972890317e..a0bea4a426 100644
--- a/libavcodec/vvc/cabac.h
+++ b/libavcodec/vvc/cabac.h
@@ -81,15 +81,15 @@ int ff_vvc_intra_luma_mpm_remainder(VVCLocalContext *lc);
 int ff_vvc_cclm_mode_flag(VVCLocalContext *lc);
 int ff_vvc_cclm_mode_idx(VVCLocalContext *lc);
 int ff_vvc_intra_chroma_pred_mode(VVCLocalContext *lc);
-int ff_vvc_palette_predictor_run(VVCLocalContext *lc);
-int ff_vvc_num_signalled_palette_entries(VVCLocalContext *lc);
+int ff_vvc_palette_predictor_run(VVCLocalContext *lc, int *value, const int max);
+int ff_vvc_num_signalled_palette_entries(VVCLocalContext *lc, int *value, const int max);
 int ff_vvc_new_palette_entries(VVCLocalContext *lc, int bit_dpeth);
 bool ff_vvc_palette_escape_val_present_flag(VVCLocalContext *lc);
 bool ff_vvc_palette_transpose_flag(VVCLocalContext *lc);
 bool ff_vvc_run_copy_flag(VVCLocalContext *lc, int prev_run_type, int prev_run_position, int cur_pos);
 bool ff_vvc_copy_above_palette_indices_flag(VVCLocalContext *lc);
 int ff_vvc_palette_idx_idc(VVCLocalContext *lc, int max_palette_index, bool adjust);
-int ff_vvc_palette_escape_val(VVCLocalContext *lc);
+int ff_vvc_palette_escape_val(VVCLocalContext *lc, int *value, const int max);
 
 //inter
 int ff_vvc_general_merge_flag(VVCLocalContext *lc);
diff --git a/libavcodec/vvc/ctu.c b/libavcodec/vvc/ctu.c
index cf7edccb8b..b0fe36e817 100644
--- a/libavcodec/vvc/ctu.c
+++ b/libavcodec/vvc/ctu.c
@@ -1850,6 +1850,7 @@ static int palette_predicted(VVCLocalContext *lc, const bool local_dual_tree, in
 {
     CodingUnit  *cu  = lc->cu;
     int nb_predicted = 0;
+    int ret;
 
     if (local_dual_tree) {
         start = LUMA;
@@ -1857,16 +1858,17 @@ static int palette_predicted(VVCLocalContext *lc, const bool local_dual_tree, in
     }
 
     for (int i = 0; i < predictor_size && nb_predicted < max_entries; i++) {
-        const int run = ff_vvc_palette_predictor_run(lc);
+        int run;
+        ret = ff_vvc_palette_predictor_run(lc, &run, predictor_size - i);
+        if (ret < 0)
+            return ret;
+
         if (run == 1)
             break;
 
         if (run > 1)
             i += run - 1;
 
-        if (i >= predictor_size)
-            return AVERROR_INVALIDDATA;
-
         predictor_reused[i] = true;
         for (int c = start; c < end; c++)
             cu->plt[c].entries[nb_predicted] = lc->ep->pp[c].entries[i];
@@ -1885,12 +1887,17 @@ static int palette_signaled(VVCLocalContext *lc, const bool local_dual_tree,
     const VVCSPS *sps         = lc->fc->ps.sps;
     CodingUnit  *cu           = lc->cu;
     const int nb_predicted    = cu->plt[start].size;
-    const int nb_signaled     = nb_predicted < max_entries ? ff_vvc_num_signalled_palette_entries(lc) : 0;
-    const int size            = nb_predicted + nb_signaled;
     const bool dual_tree_luma = local_dual_tree && cu->tree_type == DUAL_TREE_LUMA;
+    int nb_signaled, size;
 
-    if (size > max_entries || nb_signaled < 0)
-        return AVERROR_INVALIDDATA;
+    if (nb_predicted < max_entries) {
+        const int ret = ff_vvc_num_signalled_palette_entries(lc, &nb_signaled, max_entries - nb_predicted);
+        if (ret < 0)
+            return ret;
+    } else
+        nb_signaled = 0;
+
+    size = nb_predicted + nb_signaled;
 
     for (int c = start; c < end; c++) {
         Palette *plt = cu->plt + c;
@@ -2052,10 +2059,11 @@ static int palette_subblock_data(VVCLocalContext *lc,
             if (!(xc & hs) && !(yc & vs)) {
                 const int v = PALETTE_INDEX(xc, yc);
                 if (v == esc) {
-                    const int coeff = ff_vvc_palette_escape_val(lc);
-                    if (coeff >= (1U << sps->bit_depth))
-                        return AVERROR_INVALIDDATA;
-                    const int pixel = av_clip_intp2(RSHIFT(coeff * scale, 6), sps->bit_depth);
+                    int coeff, pixel;
+                    const int ret = ff_vvc_palette_escape_val(lc, &coeff, (1 << sps->bit_depth) - 1);
+                    if (ret < 0)
+                        return ret;
+                    pixel = av_clip_intp2(RSHIFT(coeff * scale, 6), sps->bit_depth);
                     PALETTE_SET_PIXEL(xc, yc, pixel);
                 } else {
                     PALETTE_SET_PIXEL(xc, yc, plt->entries[v]);
@@ -2118,9 +2126,12 @@ static int hls_palette_coding(VVCLocalContext *lc, const VVCTreeType tree_type)
     palette_qp(lc, tree_type, escape_present);
 
     index[0] = 0;
-    for (int i = 0; i <= (cu->cb_width * cu->cb_height - 1) >> 4; i++)
-        palette_subblock_data(lc, max_index, i, transpose,
+    for (int i = 0; i <= (cu->cb_width * cu->cb_height - 1) >> 4; i++) {
+        ret = palette_subblock_data(lc, max_index, i, transpose,
             run_type, index, &prev_run_pos, &adjust);
+        if (ret < 0)
+            return ret;
+    }
 
     return 0;
 }
-- 
2.47.0

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".