sandboxed-api/sandboxed_api/embed_file.cc

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// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "sandboxed_api/embed_file.h"
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include "sandboxed_api/file_toc.h"
#include "absl/strings/str_cat.h"
#include "absl/synchronization/mutex.h"
#include "sandboxed_api/sandbox2/util.h"
#include "sandboxed_api/util/fileops.h"
#include "sandboxed_api/util/raw_logging.h"
namespace sapi {
namespace {
#ifndef F_ADD_SEALS
#define F_ADD_SEALS 1033
#define F_SEAL_SEAL 0x0001
#define F_SEAL_SHRINK 0x0002
#define F_SEAL_GROW 0x0004
#define F_SEAL_WRITE 0x0008
#endif
bool SealFile(int fd) {
constexpr int kMaxRetries = 10;
for (int i = 0; i < kMaxRetries; ++i) {
if (fcntl(fd, F_ADD_SEALS,
F_SEAL_SEAL | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE) == 0) {
return true;
}
}
return false;
}
} // namespace
EmbedFile* EmbedFile::instance() {
static auto* embed_file_instance = new EmbedFile();
return embed_file_instance;
}
int EmbedFile::CreateFdForFileToc(const FileToc* toc) {
// Create a memfd/temp file and write contents of the SAPI library to it.
int fd = -1;
if (!sandbox2::util::CreateMemFd(&fd, toc->name)) {
SAPI_RAW_LOG(ERROR, "Couldn't create a temporary file for TOC name '%s'",
toc->name);
return -1;
}
file_util::fileops::FDCloser embed_fd(fd);
if (!file_util::fileops::WriteToFD(embed_fd.get(), toc->data, toc->size)) {
SAPI_RAW_PLOG(ERROR, "Couldn't write SAPI embed file '%s' to memfd file",
toc->name);
return -1;
}
// Make the underlying file non-writeable.
if (fchmod(embed_fd.get(),
S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH) == -1) {
SAPI_RAW_PLOG(ERROR, "Could't make FD=%d RX-only", embed_fd.get());
return -1;
}
// Seal the file
if (!SealFile(embed_fd.get())) {
SAPI_RAW_PLOG(ERROR, "Couldn't apply file seals to FD=%d", embed_fd.get());
return -1;
}
// Instead of working around problems with CRIU we reopen the file as
// read-only.
fd = open(absl::StrCat("/proc/", getpid(), "/fd/", embed_fd.get()).c_str(),
O_RDONLY | O_CLOEXEC);
if (fd == -1) {
SAPI_RAW_PLOG(ERROR, "Couldn't reopen '%d' read-only through /proc",
embed_fd.get());
return -1;
}
return fd;
}
int EmbedFile::GetFdForFileToc(const FileToc* toc) {
// Access to file_tocs_ must be guarded.
absl::MutexLock lock{&file_tocs_mutex_};
// If a file-descriptor for this toc already exists, just return it.
auto entry = file_tocs_.find(toc);
if (entry != file_tocs_.end()) {
SAPI_RAW_VLOG(3,
"Returning pre-existing embed file entry for '%s', fd: %d "
"(orig name: '%s')",
toc->name, entry->second, entry->first->name);
return entry->second;
}
int embed_fd = CreateFdForFileToc(toc);
if (embed_fd == -1) {
SAPI_RAW_LOG(ERROR, "Cannot create a file for FileTOC: '%s'", toc->name);
return -1;
}
SAPI_RAW_VLOG(1, "Created new embed file entry for '%s' with fd: %d",
toc->name, embed_fd);
file_tocs_[toc] = embed_fd;
return embed_fd;
}
int EmbedFile::GetDupFdForFileToc(const FileToc* toc) {
int fd = GetFdForFileToc(toc);
if (fd == -1) {
return -1;
}
fd = dup(fd);
if (fd == -1) {
SAPI_RAW_PLOG(ERROR, "dup failed");
}
return fd;
}
} // namespace sapi