| blackeangel |
07-01-2017 10:06 2701435 |
Объясните готовый код
Код:
#include "file_contexts.h"
#include "mbutil/autoclose/file.h"
#include <memory>
#include <string>
#include <utility>
#include <vector>
#include <cstdlib>
#include <getopt.h>
#define SELINUX_MAGIC_COMPILED_FCONTEXT 0xf97cff8a
#define SELINUX_COMPILED_FCONTEXT_NOPCRE_VERS 1
#define SELINUX_COMPILED_FCONTEXT_PCRE_VERS 2
#define SELINUX_COMPILED_FCONTEXT_MODE 3
#define SELINUX_COMPILED_FCONTEXT_PREFIX_LEN 4
#define SELINUX_COMPILED_FCONTEXT_MAX_VERS \
SELINUX_COMPILED_FCONTEXT_PREFIX_LEN
namespace mb
{
typedef std::vector<std::pair<std::string, std::string>> ContextsList;
typedef std::unique_ptr<char, void (*)(void *)> ScopedCharPtr;
static bool skip_pcre(FILE *fp)
{
size_t n;
uint32_t entry_len;
// Skip PCRE regex
n = fread(&entry_len, 1, sizeof(entry_len), fp);
if (n != sizeof(entry_len) || entry_len == 0) {
return false;
}
if (fseek(fp, entry_len, SEEK_CUR) != 0) {
return false;
}
// Skip PCRE study data
n = fread(&entry_len, 1, sizeof(entry_len), fp);
if (n != sizeof(entry_len) || entry_len == 0) {
return false;
}
if (fseek(fp, entry_len, SEEK_CUR) != 0) {
return false;
}
return true;
}
static bool load_file(FILE *fp, ContextsList *list)
{
size_t n;
uint32_t magic;
uint32_t version;
uint32_t entry_len;
uint32_t stem_map_len;
uint32_t regex_array_len;
// Check magic
n = fread(&magic, 1, sizeof(magic), fp);
if (n != sizeof(magic) || magic != SELINUX_MAGIC_COMPILED_FCONTEXT) {
return false;
}
// Check version
n = fread(&version, 1, sizeof(version), fp);
if (n != sizeof(version) || version > SELINUX_COMPILED_FCONTEXT_MAX_VERS) {
return false;
}
// Skip regex version
if (version >= SELINUX_COMPILED_FCONTEXT_PCRE_VERS) {
n = fread(&entry_len, 1, sizeof(entry_len), fp);
if (n != sizeof(entry_len)) {
return false;
}
if (fseek(fp, entry_len, SEEK_CUR) != 0) {
return false;
}
}
// Skip stem map
n = fread(&stem_map_len, 1, sizeof(stem_map_len), fp);
if (n != sizeof(stem_map_len) || stem_map_len == 0) {
return false;
}
for (uint32_t i = 0; i < stem_map_len; ++i) {
uint32_t stem_len;
// Length does not include NULL-terminator
n = fread(&stem_len, 1, sizeof(stem_len), fp);
if (n != sizeof(stem_len) || stem_len == 0) {
return false;
}
if (stem_len < UINT32_MAX) {
if (fseek(fp, stem_len + 1, SEEK_CUR) != 0) {
return false;
}
} else {
return false;
}
}
// Load regexes
n = fread(®ex_array_len, 1, sizeof(regex_array_len), fp);
if (n != sizeof(regex_array_len) || regex_array_len == 0) {
return false;
}
for (uint32_t i = 0; i < regex_array_len; ++i) {
// Read context string
n = fread(&entry_len, 1, sizeof(entry_len), fp);
if (n != sizeof(uint32_t) || entry_len == 0) {
return false;
}
ScopedCharPtr context(static_cast<char *>(malloc(entry_len)), &free);
if (!context) {
return false;
}
n = fread(context.get(), 1, entry_len, fp);
if (n != entry_len) {
return false;
}
if (context.get()[entry_len - 1] != '\0') {
return false;
}
// Read regex string
n = fread(&entry_len, 1, sizeof(entry_len), fp);
if (n != sizeof(entry_len) || entry_len == 0) {
return false;
}
ScopedCharPtr regex(static_cast<char *>(malloc(entry_len)), &free);
if (!regex) {
return false;
}
n = fread(regex.get(), 1, entry_len, fp);
if (n != entry_len) {
return false;
}
if (regex.get()[entry_len - 1] != '\0') {
return false;
}
// Skip mode
if (version >= SELINUX_COMPILED_FCONTEXT_MODE) {
if (fseek(fp, sizeof(uint32_t), SEEK_CUR) != 0) {
return false;
}
} else {
if (fseek(fp, sizeof(mode_t), SEEK_CUR) != 0) {
return false;
}
}
// Skip stem ID
if (fseek(fp, sizeof(uint32_t), SEEK_CUR) != 0) {
return false;
}
// Skip meta chars
if (fseek(fp, sizeof(uint32_t), SEEK_CUR) != 0) {
return false;
}
if (version >= SELINUX_COMPILED_FCONTEXT_PREFIX_LEN) {
// Skip prefix length
if (fseek(fp, sizeof(uint32_t), SEEK_CUR) != 0) {
return false;
}
}
// Skip PCRE stuff
if (!skip_pcre(fp)) {
return false;
}
list->emplace_back(context.get(), regex.get());
}
return true;
}
FileContextsResult patch_file_contexts(const char *source_path,
const char *target_path)
{
ContextsList list;
autoclose::file fp_old(autoclose::fopen(source_path, "rb"));
if (!fp_old) {
return FileContextsResult::ERRNO;
}
if (!load_file(fp_old.get(), &list)) {
return FileContextsResult::PARSE_ERROR;
}
fp_old.reset();
autoclose::file fp_new(autoclose::fopen(target_path, "w"));
if (!fp_new) {
return FileContextsResult::ERRNO;
}
for (auto const &pair : list) {
auto const &context = pair.first;
auto const ®ex = pair.second;
if (fputs(regex.c_str(), fp_new.get()) == EOF
|| fputc(' ', fp_new.get()) == EOF
|| fputs(context.c_str(), fp_new.get()) == EOF
|| fputc('\n', fp_new.get()) == EOF) {
return FileContextsResult::ERRNO;
}
}
return FileContextsResult::OK;
}
static void file_contexts_usage(FILE *stream)
{
fprintf(stream,
"Usage: file_contexts [OPTION]... <input> <output>\n\n"
"Options:\n"
" -h, --help Display this help message\n");
}
int file_contexts_main(int argc, char *argv[])
{
int opt;
static const char *short_options = "h";
static struct option long_options[] = {
{"help", no_argument, 0, 'h'},
{0, 0, 0, 0}
};
int long_index = 0;
while ((opt = getopt_long(argc, argv, short_options,
long_options, &long_index)) != -1) {
switch (opt) {
case 'h':
file_contexts_usage(stdout);
return EXIT_SUCCESS;
default:
file_contexts_usage(stderr);
return EXIT_FAILURE;
}
}
if (argc - optind != 2) {
file_contexts_usage(stderr);
return EXIT_FAILURE;
}
const char *input = argv[optind];
const char *output = argv[optind + 1];
auto ret = patch_file_contexts(input, output);
return ret == FileContextsResult::OK ? EXIT_SUCCESS : EXIT_FAILURE;
}
}
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