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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "pdf/font_table_linux.h"
#include <sys/stat.h>
#include <unistd.h>
#include <algorithm>
#include <limits>
#include <memory>
#include "base/numerics/safe_conversions.h"
#include "base/posix/eintr_wrapper.h"
#include "base/sys_byteorder.h"
namespace pdf {
// TODO(drott): This should be should be replaced with using FreeType for the
// purpose instead of reimplementing table parsing.
bool GetFontTable(int fd,
uint32_t table_tag,
off_t offset,
uint8_t* output,
size_t* output_length) {
if (offset < 0)
return false;
size_t data_length = 0; // the length of the file data.
off_t data_offset = 0; // the offset of the data in the file.
if (table_tag == 0) {
// Get the entire font file.
struct stat st;
if (fstat(fd, &st) < 0)
return false;
data_length = base::checked_cast<size_t>(st.st_size);
} else {
// Get a font table. Read the header to find its offset in the file.
uint16_t num_tables;
ssize_t n = HANDLE_EINTR(
pread(fd, &num_tables, sizeof(num_tables), 4 /* skip the font type */));
if (n != sizeof(num_tables))
return false;
// Font data is stored in net (big-endian) order.
num_tables = base::NetToHost16(num_tables);
// Read the table directory.
static const size_t kTableEntrySize = 16;
const size_t directory_size = num_tables * kTableEntrySize;
std::unique_ptr<uint8_t[]> table_entries(new uint8_t[directory_size]);
n = HANDLE_EINTR(pread(fd, table_entries.get(), directory_size,
12 /* skip the SFNT header */));
if (n != base::checked_cast<ssize_t>(directory_size))
return false;
for (uint16_t i = 0; i < num_tables; ++i) {
uint8_t* entry = table_entries.get() + i * kTableEntrySize;
uint32_t tag = *reinterpret_cast<uint32_t*>(entry);
if (tag == table_tag) {
// Font data is stored in net (big-endian) order.
data_offset =
base::NetToHost32(*reinterpret_cast<uint32_t*>(entry + 8));
data_length =
base::NetToHost32(*reinterpret_cast<uint32_t*>(entry + 12));
break;
}
}
}
if (!data_length)
return false;
// Clamp |offset| inside the allowable range. This allows the read to succeed
// but return 0 bytes.
offset = std::min(offset, base::checked_cast<off_t>(data_length));
// Make sure it's safe to add the data offset and the caller's logical offset.
// Define the maximum positive offset on 32 bit systems.
static const off_t kMaxPositiveOffset32 = 0x7FFFFFFF; // 2 GB - 1.
if ((offset > kMaxPositiveOffset32 / 2) ||
(data_offset > kMaxPositiveOffset32 / 2))
return false;
data_offset += offset;
data_length -= offset;
if (output) {
// 'output_length' holds the maximum amount of data the caller can accept.
data_length = std::min(data_length, *output_length);
ssize_t n = HANDLE_EINTR(pread(fd, output, data_length, data_offset));
if (n != base::checked_cast<ssize_t>(data_length))
return false;
}
*output_length = data_length;
return true;
}
} // namespace pdf
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