From 4619a48fc3292743d7ce9658bee4245406734109 Mon Sep 17 00:00:00 2001
From: Vincent Rabaud <vrabaud@google.com>
Date: Thu, 7 Sep 2023 21:16:03 +0200
Subject: [PATCH] Fix OOB write in BuildHuffmanTable.

First, BuildHuffmanTable is called to check if the data is valid.
If it is and the table is not big enough, more memory is allocated.

This will make sure that valid (but unoptimized because of unbalanced
codes) streams are still decodable.

Bug: chromium:1479274
Change-Id: I31c36dbf3aa78d35ecf38706b50464fd3d375741
(cherry picked from commit 902bc9190331343b2017211debcec8d2ab87e17a)
(cherry picked from commit 2af26267cdfcb63a88e5c74a85927a12d6ca1d76)
---
 src/dec/vp8l_dec.c        | 46 ++++++++++---------
 src/dec/vp8li_dec.h       |  2 +-
 src/utils/huffman_utils.c | 97 +++++++++++++++++++++++++++++++--------
 src/utils/huffman_utils.h | 27 +++++++++--
 4 files changed, 129 insertions(+), 43 deletions(-)

diff --git a/src/dec/vp8l_dec.c b/src/dec/vp8l_dec.c
index c0ea0181e5..7995313fa1 100644
--- a/src/dec/vp8l_dec.c
+++ b/src/dec/vp8l_dec.c
@@ -253,11 +253,11 @@ static int ReadHuffmanCodeLengths(
   int symbol;
   int max_symbol;
   int prev_code_len = DEFAULT_CODE_LENGTH;
-  HuffmanCode table[1 << LENGTHS_TABLE_BITS];
+  HuffmanTables tables;

-  if (!VP8LBuildHuffmanTable(table, LENGTHS_TABLE_BITS,
-                             code_length_code_lengths,
-                             NUM_CODE_LENGTH_CODES)) {
+  if (!VP8LHuffmanTablesAllocate(1 << LENGTHS_TABLE_BITS, &tables) ||
+      !VP8LBuildHuffmanTable(&tables, LENGTHS_TABLE_BITS,
+                             code_length_code_lengths, NUM_CODE_LENGTH_CODES)) {
     goto End;
   }

@@ -277,7 +277,7 @@ static int ReadHuffmanCodeLengths(
     int code_len;
     if (max_symbol-- == 0) break;
     VP8LFillBitWindow(br);
-    p = &table[VP8LPrefetchBits(br) & LENGTHS_TABLE_MASK];
+    p = &tables.curr_segment->start[VP8LPrefetchBits(br) & LENGTHS_TABLE_MASK];
     VP8LSetBitPos(br, br->bit_pos_ + p->bits);
     code_len = p->value;
     if (code_len < kCodeLengthLiterals) {
@@ -300,6 +300,7 @@ static int ReadHuffmanCodeLengths(
   ok = 1;

  End:
+  VP8LHuffmanTablesDeallocate(&tables);
   if (!ok) dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
   return ok;
 }
@@ -307,7 +308,8 @@ static int ReadHuffmanCodeLengths(
 // 'code_lengths' is pre-allocated temporary buffer, used for creating Huffman
 // tree.
 static int ReadHuffmanCode(int alphabet_size, VP8LDecoder* const dec,
-                           int* const code_lengths, HuffmanCode* const table) {
+                           int* const code_lengths,
+                           HuffmanTables* const table) {
   int ok = 0;
   int size = 0;
   VP8LBitReader* const br = &dec->br_;
@@ -362,8 +364,7 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
   VP8LMetadata* const hdr = &dec->hdr_;
   uint32_t* huffman_image = NULL;
   HTreeGroup* htree_groups = NULL;
-  HuffmanCode* huffman_tables = NULL;
-  HuffmanCode* huffman_table = NULL;
+  HuffmanTables* huffman_tables = &hdr->huffman_tables_;
   int num_htree_groups = 1;
   int num_htree_groups_max = 1;
   int max_alphabet_size = 0;
@@ -372,6 +373,10 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
   int* mapping = NULL;
   int ok = 0;

+  // Check the table has been 0 initialized (through InitMetadata).
+  assert(huffman_tables->root.start == NULL);
+  assert(huffman_tables->curr_segment == NULL);
+
   if (allow_recursion && VP8LReadBits(br, 1)) {
     // use meta Huffman codes.
     const int huffman_precision = VP8LReadBits(br, 3) + 2;
@@ -434,16 +439,15 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,

   code_lengths = (int*)WebPSafeCalloc((uint64_t)max_alphabet_size,
                                       sizeof(*code_lengths));
-  huffman_tables = (HuffmanCode*)WebPSafeMalloc(num_htree_groups * table_size,
-                                                sizeof(*huffman_tables));
   htree_groups = VP8LHtreeGroupsNew(num_htree_groups);

-  if (htree_groups == NULL || code_lengths == NULL || huffman_tables == NULL) {
+  if (htree_groups == NULL || code_lengths == NULL ||
+      !VP8LHuffmanTablesAllocate(num_htree_groups * table_size,
+                                 huffman_tables)) {
     dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
     goto Error;
   }

-  huffman_table = huffman_tables;
   for (i = 0; i < num_htree_groups_max; ++i) {
     // If the index "i" is unused in the Huffman image, just make sure the
     // coefficients are valid but do not store them.
@@ -468,19 +472,20 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
       int max_bits = 0;
       for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; ++j) {
         int alphabet_size = kAlphabetSize[j];
-        htrees[j] = huffman_table;
         if (j == 0 && color_cache_bits > 0) {
           alphabet_size += (1 << color_cache_bits);
         }
-        size = ReadHuffmanCode(alphabet_size, dec, code_lengths, huffman_table);
+        size =
+            ReadHuffmanCode(alphabet_size, dec, code_lengths, huffman_tables);
+        htrees[j] = huffman_tables->curr_segment->curr_table;
         if (size == 0) {
           goto Error;
         }
         if (is_trivial_literal && kLiteralMap[j] == 1) {
-          is_trivial_literal = (huffman_table->bits == 0);
+          is_trivial_literal = (htrees[j]->bits == 0);
         }
-        total_size += huffman_table->bits;
-        huffman_table += size;
+        total_size += htrees[j]->bits;
+        huffman_tables->curr_segment->curr_table += size;
         if (j <= ALPHA) {
           int local_max_bits = code_lengths[0];
           int k;
@@ -515,14 +520,13 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
   hdr->huffman_image_ = huffman_image;
   hdr->num_htree_groups_ = num_htree_groups;
   hdr->htree_groups_ = htree_groups;
-  hdr->huffman_tables_ = huffman_tables;

  Error:
   WebPSafeFree(code_lengths);
   WebPSafeFree(mapping);
   if (!ok) {
     WebPSafeFree(huffman_image);
-    WebPSafeFree(huffman_tables);
+    VP8LHuffmanTablesDeallocate(huffman_tables);
     VP8LHtreeGroupsFree(htree_groups);
   }
   return ok;
@@ -1358,7 +1362,7 @@ static void ClearMetadata(VP8LMetadata* const hdr) {
   assert(hdr != NULL);

   WebPSafeFree(hdr->huffman_image_);
-  WebPSafeFree(hdr->huffman_tables_);
+  VP8LHuffmanTablesDeallocate(&hdr->huffman_tables_);
   VP8LHtreeGroupsFree(hdr->htree_groups_);
   VP8LColorCacheClear(&hdr->color_cache_);
   VP8LColorCacheClear(&hdr->saved_color_cache_);
@@ -1673,7 +1677,7 @@ int VP8LDecodeImage(VP8LDecoder* const dec) {

   if (dec == NULL) return 0;

-  assert(dec->hdr_.huffman_tables_ != NULL);
+  assert(dec->hdr_.huffman_tables_.root.start != NULL);
   assert(dec->hdr_.htree_groups_ != NULL);
   assert(dec->hdr_.num_htree_groups_ > 0);

diff --git a/src/dec/vp8li_dec.h b/src/dec/vp8li_dec.h
index 72b2e86120..32540a4b88 100644
--- a/src/dec/vp8li_dec.h
+++ b/src/dec/vp8li_dec.h
@@ -51,7 +51,7 @@ typedef struct {
   uint32_t*       huffman_image_;
   int             num_htree_groups_;
   HTreeGroup*     htree_groups_;
-  HuffmanCode*    huffman_tables_;
+  HuffmanTables   huffman_tables_;
 } VP8LMetadata;

 typedef struct VP8LDecoder VP8LDecoder;
diff --git a/src/utils/huffman_utils.c b/src/utils/huffman_utils.c
index 90c2fbf7c1..cf73abd437 100644
--- a/src/utils/huffman_utils.c
+++ b/src/utils/huffman_utils.c
@@ -177,21 +177,24 @@ static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
       if (num_open < 0) {
         return 0;
       }
-      if (root_table == NULL) continue;
       for (; count[len] > 0; --count[len]) {
         HuffmanCode code;
         if ((key & mask) != low) {
-          table += table_size;
+          if (root_table != NULL) table += table_size;
           table_bits = NextTableBitSize(count, len, root_bits);
           table_size = 1 << table_bits;
           total_size += table_size;
           low = key & mask;
-          root_table[low].bits = (uint8_t)(table_bits + root_bits);
-          root_table[low].value = (uint16_t)((table - root_table) - low);
+          if (root_table != NULL) {
+            root_table[low].bits = (uint8_t)(table_bits + root_bits);
+            root_table[low].value = (uint16_t)((table - root_table) - low);
+          }
+        }
+        if (root_table != NULL) {
+          code.bits = (uint8_t)(len - root_bits);
+          code.value = (uint16_t)sorted[symbol++];
+          ReplicateValue(&table[key >> root_bits], step, table_size, code);
         }
-        code.bits = (uint8_t)(len - root_bits);
-        code.value = (uint16_t)sorted[symbol++];
-        ReplicateValue(&table[key >> root_bits], step, table_size, code);
         key = GetNextKey(key, len);
       }
     }
@@ -211,25 +214,83 @@ static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
   ((1 << MAX_CACHE_BITS) + NUM_LITERAL_CODES + NUM_LENGTH_CODES)
 // Cut-off value for switching between heap and stack allocation.
 #define SORTED_SIZE_CUTOFF 512
-int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
+int VP8LBuildHuffmanTable(HuffmanTables* const root_table, int root_bits,
                           const int code_lengths[], int code_lengths_size) {
-  int total_size;
+  const int total_size =
+      BuildHuffmanTable(NULL, root_bits, code_lengths, code_lengths_size, NULL);
   assert(code_lengths_size <= MAX_CODE_LENGTHS_SIZE);
-  if (root_table == NULL) {
-    total_size = BuildHuffmanTable(NULL, root_bits,
-                                   code_lengths, code_lengths_size, NULL);
-  } else if (code_lengths_size <= SORTED_SIZE_CUTOFF) {
+  if (total_size == 0 || root_table == NULL) return total_size;
+
+  if (root_table->curr_segment->curr_table + total_size >=
+      root_table->curr_segment->start + root_table->curr_segment->size) {
+    // If 'root_table' does not have enough memory, allocate a new segment.
+    // The available part of root_table->curr_segment is left unused because we
+    // need a contiguous buffer.
+    const int segment_size = root_table->curr_segment->size;
+    struct HuffmanTablesSegment* next =
+        (HuffmanTablesSegment*)WebPSafeMalloc(1, sizeof(*next));
+    if (next == NULL) return 0;
+    // Fill the new segment.
+    // We need at least 'total_size' but if that value is small, it is better to
+    // allocate a big chunk to prevent more allocations later. 'segment_size' is
+    // therefore chosen (any other arbitrary value could be chosen).
+    next->size = total_size > segment_size ? total_size : segment_size;
+    next->start =
+        (HuffmanCode*)WebPSafeMalloc(next->size, sizeof(*next->start));
+    if (next->start == NULL) {
+      WebPSafeFree(next);
+      return 0;
+    }
+    next->curr_table = next->start;
+    next->next = NULL;
+    // Point to the new segment.
+    root_table->curr_segment->next = next;
+    root_table->curr_segment = next;
+  }
+  if (code_lengths_size <= SORTED_SIZE_CUTOFF) {
     // use local stack-allocated array.
     uint16_t sorted[SORTED_SIZE_CUTOFF];
-    total_size = BuildHuffmanTable(root_table, root_bits,
-                                   code_lengths, code_lengths_size, sorted);
-  } else {   // rare case. Use heap allocation.
+    BuildHuffmanTable(root_table->curr_segment->curr_table, root_bits,
+                      code_lengths, code_lengths_size, sorted);
+  } else {  // rare case. Use heap allocation.
     uint16_t* const sorted =
         (uint16_t*)WebPSafeMalloc(code_lengths_size, sizeof(*sorted));
     if (sorted == NULL) return 0;
-    total_size = BuildHuffmanTable(root_table, root_bits,
-                                   code_lengths, code_lengths_size, sorted);
+    BuildHuffmanTable(root_table->curr_segment->curr_table, root_bits,
+                      code_lengths, code_lengths_size, sorted);
     WebPSafeFree(sorted);
   }
   return total_size;
 }
+
+int VP8LHuffmanTablesAllocate(int size, HuffmanTables* huffman_tables) {
+  // Have 'segment' point to the first segment for now, 'root'.
+  HuffmanTablesSegment* const root = &huffman_tables->root;
+  huffman_tables->curr_segment = root;
+  // Allocate root.
+  root->start = (HuffmanCode*)WebPSafeMalloc(size, sizeof(*root->start));
+  if (root->start == NULL) return 0;
+  root->curr_table = root->start;
+  root->next = NULL;
+  root->size = size;
+  return 1;
+}
+
+void VP8LHuffmanTablesDeallocate(HuffmanTables* const huffman_tables) {
+  HuffmanTablesSegment *current, *next;
+  if (huffman_tables == NULL) return;
+  // Free the root node.
+  current = &huffman_tables->root;
+  next = current->next;
+  WebPSafeFree(current->start);
+  current->start = NULL;
+  current->next = NULL;
+  current = next;
+  // Free the following nodes.
+  while (current != NULL) {
+    next = current->next;
+    WebPSafeFree(current->start);
+    WebPSafeFree(current);
+    current = next;
+  }
+}
diff --git a/src/utils/huffman_utils.h b/src/utils/huffman_utils.h
index 13b7ad1ac4..98415c5328 100644
--- a/src/utils/huffman_utils.h
+++ b/src/utils/huffman_utils.h
@@ -43,6 +43,29 @@ typedef struct {
                     // or non-literal symbol otherwise
 } HuffmanCode32;

+// Contiguous memory segment of HuffmanCodes.
+typedef struct HuffmanTablesSegment {
+  HuffmanCode* start;
+  // Pointer to where we are writing into the segment. Starts at 'start' and
+  // cannot go beyond 'start' + 'size'.
+  HuffmanCode* curr_table;
+  // Pointer to the next segment in the chain.
+  struct HuffmanTablesSegment* next;
+  int size;
+} HuffmanTablesSegment;
+
+// Chained memory segments of HuffmanCodes.
+typedef struct HuffmanTables {
+  HuffmanTablesSegment root;
+  // Currently processed segment. At first, this is 'root'.
+  HuffmanTablesSegment* curr_segment;
+} HuffmanTables;
+
+// Allocates a HuffmanTables with 'size' contiguous HuffmanCodes. Returns 0 on
+// memory allocation error, 1 otherwise.
+int VP8LHuffmanTablesAllocate(int size, HuffmanTables* huffman_tables);
+void VP8LHuffmanTablesDeallocate(HuffmanTables* const huffman_tables);
+
 #define HUFFMAN_PACKED_BITS 6
 #define HUFFMAN_PACKED_TABLE_SIZE (1u << HUFFMAN_PACKED_BITS)

@@ -78,9 +101,7 @@ void VP8LHtreeGroupsFree(HTreeGroup* const htree_groups);
 // the huffman table.
 // Returns built table size or 0 in case of error (invalid tree or
 // memory error).
-// If root_table is NULL, it returns 0 if a lookup cannot be built, something
-// > 0 otherwise (but not the table size).
-int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
+int VP8LBuildHuffmanTable(HuffmanTables* const root_table, int root_bits,
                           const int code_lengths[], int code_lengths_size);

 #ifdef __cplusplus
