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.
(cherry picked from commit 902bc91)

Change-Id: I3abe4db460dcac62c14a84832284c0b530630af2

src/dec/vp8l.c

@@ -252,11 +252,11 @@ 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,
+  if (!VP8LHuffmanTablesAllocate(1 << LENGTHS_TABLE_BITS, &tables) ||
-                             code_length_code_lengths,
+      !VP8LBuildHuffmanTable(&tables, LENGTHS_TABLE_BITS,
-                             NUM_CODE_LENGTH_CODES)) {
+                             code_length_code_lengths, NUM_CODE_LENGTH_CODES)) {
     goto End;
   }
 
@@ -276,7 +276,7 @@ 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) {
@@ -299,6 +299,7 @@ static int ReadHuffmanCodeLengths(
   ok = 1;
 
  End:
+  VP8LHuffmanTablesDeallocate(&tables);
   if (!ok) dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
   return ok;
 }
@@ -306,7 +307,8 @@ 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_;
@@ -361,8 +363,7 @@ 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;
+  HuffmanTables* huffman_tables = &hdr->huffman_tables_;
-  HuffmanCode* huffman_table = NULL;
   int num_htree_groups = 1;
   int num_htree_groups_max = 1;
   int max_alphabet_size = 0;
@@ -371,6 +372,10 @@ 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;
@@ -431,18 +436,17 @@ static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
     }
   }
 
-  huffman_tables = (HuffmanCode*)WebPSafeMalloc(num_htree_groups * table_size,
-                                                sizeof(*huffman_tables));
   htree_groups = VP8LHtreeGroupsNew(num_htree_groups);
   code_lengths = (int*)WebPSafeCalloc((uint64_t)max_alphabet_size,
                                       sizeof(*code_lengths));
 
-  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.
@@ -467,19 +471,20 @@ 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;
+        total_size += htrees[j]->bits;
-        huffman_table += size;
+        huffman_tables->curr_segment->curr_table += size;
         if (j <= ALPHA) {
           int local_max_bits = code_lengths[0];
           int k;
@@ -514,14 +519,13 @@ 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;
@@ -1329,7 +1333,7 @@ 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_);
@@ -1644,7 +1648,7 @@ int VP8LDecodeImage(VP8LDecoder* const dec) {
   // Sanity checks.
   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);
 

src/dec/vp8li.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;

src/utils/huffman.c

@@ -75,11 +75,13 @@ static WEBP_INLINE int NextTableBitSize(const int* const count,
   return len - root_bits;
 }
 
-int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
+// sorted[code_lengths_size] is a pre-allocated array for sorting symbols
-                          const int code_lengths[], int code_lengths_size) {
+// by code length.
+static int BuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
+                             const int code_lengths[], int code_lengths_size,
+                             uint16_t sorted[]) {
   HuffmanCode* table = root_table;  // next available space in table
   int total_size = 1 << root_bits;  // total size root table + 2nd level table
-  int* sorted = NULL;               // symbols sorted by code length
   int len;                          // current code length
   int symbol;                       // symbol index in original or sorted table
   // number of codes of each length:
@@ -89,7 +91,8 @@ int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
 
   assert(code_lengths_size != 0);
   assert(code_lengths != NULL);
-  assert(root_table != NULL);
+  assert((root_table != NULL && sorted != NULL) ||
+         (root_table == NULL && sorted == NULL));
   assert(root_bits > 0);
 
   // Build histogram of code lengths.
@@ -114,26 +117,26 @@ int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
     offset[len + 1] = offset[len] + count[len];
   }
 
-  sorted = (int*)WebPSafeMalloc(code_lengths_size, sizeof(*sorted));
-  if (sorted == NULL) {
-    return 0;
-  }
-
   // Sort symbols by length, by symbol order within each length.
   for (symbol = 0; symbol < code_lengths_size; ++symbol) {
     const int symbol_code_length = code_lengths[symbol];
     if (code_lengths[symbol] > 0) {
+      if (sorted != NULL) {
         sorted[offset[symbol_code_length]++] = symbol;
+      } else {
+        offset[symbol_code_length]++;
+      }
     }
   }
 
   // Special case code with only one value.
   if (offset[MAX_ALLOWED_CODE_LENGTH] == 1) {
+    if (sorted != NULL) {
       HuffmanCode code;
       code.bits = 0;
       code.value = (uint16_t)sorted[0];
       ReplicateValue(table, 1, total_size, code);
-    WebPSafeFree(sorted);
+    }
     return total_size;
   }
 
@@ -153,9 +156,9 @@ int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
       num_nodes += num_open;
       num_open -= count[len];
       if (num_open < 0) {
-        WebPSafeFree(sorted);
         return 0;
       }
+      if (root_table == NULL) continue;
       for (; count[len] > 0; --count[len]) {
         HuffmanCode code;
         code.bits = (uint8_t)len;
@@ -172,34 +175,122 @@ int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
       num_nodes += num_open;
       num_open -= count[len];
       if (num_open < 0) {
-        WebPSafeFree(sorted);
         return 0;
       }
       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;
+          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);
+        }
         key = GetNextKey(key, len);
       }
     }
 
     // Check if tree is full.
     if (num_nodes != 2 * offset[MAX_ALLOWED_CODE_LENGTH] - 1) {
-      WebPSafeFree(sorted);
       return 0;
     }
   }
 
-  WebPSafeFree(sorted);
   return total_size;
 }
+
+// Maximum code_lengths_size is 2328 (reached for 11-bit color_cache_bits).
+// More commonly, the value is around ~280.
+#define MAX_CODE_LENGTHS_SIZE \
+  ((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(HuffmanTables* const root_table, int root_bits,
+                          const int code_lengths[], int code_lengths_size) {
+  const int total_size =
+      BuildHuffmanTable(NULL, root_bits, code_lengths, code_lengths_size, NULL);
+  assert(code_lengths_size <= MAX_CODE_LENGTHS_SIZE);
+  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];
+    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;
+    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;
+  }
+}

src/utils/huffman.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)
 
@@ -78,7 +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).
-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