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Fix OOB write in BuildHuffmanTable.
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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 902bc91)
(cherry picked from commit 2af2626)
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@vrabaud @jzern
vrabaud authored and jzern committed Sep 7, 2023
1 parent d01505c commit 8d9916d
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Showing 4 changed files with 129 additions and 43 deletions.
46 changes: 25 additions & 21 deletions src/dec/vp8l_dec.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}

Expand All @@ -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) {
Expand All @@ -300,14 +300,16 @@ static int ReadHuffmanCodeLengths(
ok = 1;

End:
VP8LHuffmanTablesDeallocate(&tables);
if (!ok) dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
return ok;
}

// '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_;
Expand Down Expand Up @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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.
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -1354,7 +1358,7 @@ 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_);
Expand Down Expand Up @@ -1670,7 +1674,7 @@ 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);

Expand Down
2 changes: 1 addition & 1 deletion src/dec/vp8li_dec.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
97 changes: 79 additions & 18 deletions src/utils/huffman_utils.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
}
Expand All @@ -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;
}
}
27 changes: 24 additions & 3 deletions src/utils/huffman_utils.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)

Expand Down Expand Up @@ -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
Expand Down

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