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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/shared_memory.h"
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#ifdef ANDROID
# include "mozilla/Ashmem.h"
#endif
#ifdef XP_LINUX
# include "linux_memfd_defs.h"
#endif
#ifdef MOZ_WIDGET_GTK
# include "mozilla/WidgetUtilsGtk.h"
#endif
#ifdef __FreeBSD__
# include <sys/capsicum.h>
#endif
#ifdef MOZ_VALGRIND
# include <valgrind/valgrind.h>
#endif
#include "base/eintr_wrapper.h"
#include "base/logging.h"
#include "base/string_util.h"
#include "mozilla/Atomics.h"
#include "mozilla/Maybe.h"
#include "mozilla/ProfilerThreadSleep.h"
#include "mozilla/UniquePtrExtensions.h"
#include "prenv.h"
namespace base {
void SharedMemory::MappingDeleter::operator()(void* ptr) {
// Check that this isn't a default-constructed deleter. (`munmap`
// is specified to fail with `EINVAL` if the length is 0, so this
// assertion isn't load-bearing.)
DCHECK(mapped_size_ != 0);
munmap(ptr, mapped_size_);
// Guard against multiple calls of the same deleter, which shouldn't
// happen (but could, if `UniquePtr::reset` were used). Calling
// `munmap` with an incorrect non-zero length would be bad.
mapped_size_ = 0;
}
SharedMemory::~SharedMemory() {
// This is almost equal to the default destructor, except for the
// warning message about unfrozen freezable memory.
Close();
}
bool SharedMemory::SetHandle(SharedMemoryHandle handle, bool read_only) {
DCHECK(!mapped_file_);
#ifndef ANDROID
DCHECK(!frozen_file_);
#endif
freezeable_ = false;
mapped_file_ = std::move(handle);
read_only_ = read_only;
// is_memfd_ only matters for freezing, which isn't possible
return true;
}
// static
bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
return handle != nullptr;
}
// static
SharedMemoryHandle SharedMemory::NULLHandle() { return nullptr; }
// static
bool SharedMemory::UsingPosixShm() {
// Undocumented feature of AppendPosixShmPrefix to reduce code
// duplication: if the string pointer is null, it's ignored.
return AppendPosixShmPrefix(nullptr, 0);
}
#ifdef ANDROID
// Android has its own shared memory API, ashmem. It doesn't support
// POSIX shm_open, and the memfd support (see below) also doesn't work
// because its SELinux policy prevents the procfs operations we'd use
// static
bool SharedMemory::AppendPosixShmPrefix(std::string* str, pid_t pid) {
return false;
}
bool SharedMemory::CreateInternal(size_t size, bool freezeable) {
read_only_ = false;
DCHECK(size > 0);
DCHECK(!mapped_file_);
int fd = mozilla::android::ashmem_create(nullptr, size);
if (fd < 0) {
CHROMIUM_LOG(WARNING) << "failed to open shm: " << strerror(errno);
return false;
}
mapped_file_.reset(fd);
max_size_ = size;
freezeable_ = freezeable;
return true;
}
bool SharedMemory::ReadOnlyCopy(SharedMemory* ro_out) {
DCHECK(mapped_file_);
DCHECK(!read_only_);
CHECK(freezeable_);
if (ro_out == this) {
DCHECK(!memory_);
}
if (mozilla::android::ashmem_setProt(mapped_file_.get(), PROT_READ) != 0) {
CHROMIUM_LOG(WARNING) << "failed to set ashmem read-only: "
<< strerror(errno);
return false;
}
mozilla::UniqueFileHandle ro_file = std::move(mapped_file_);
freezeable_ = false;
ro_out->Close();
ro_out->mapped_file_ = std::move(ro_file);
ro_out->max_size_ = max_size_;
ro_out->read_only_ = true;
ro_out->freezeable_ = false;
return true;
}
#else // not Android
// memfd_create is a nonstandard interface for creating anonymous
// shared memory accessible as a file descriptor but not tied to any
// filesystem. It first appeared in Linux 3.17, and was adopted by
// FreeBSD in version 13.
# if !defined(HAVE_MEMFD_CREATE) && defined(XP_LINUX) && \
defined(SYS_memfd_create)
// Older libc versions (e.g., glibc before 2.27) don't have the
// wrapper, but we can supply our own; see `linux_memfd_defs.h`.
static int memfd_create(const char* name, unsigned int flags) {
return syscall(SYS_memfd_create, name, flags);
}
# define HAVE_MEMFD_CREATE 1
# endif
// memfd supports having "seals" applied to the file, to prevent
// various types of changes (which apply to all fds referencing the
// file). Unfortunately, we can't rely on F_SEAL_WRITE to implement
// Freeze(); see the comments in ReadOnlyCopy() below.
//
// Instead, to prevent a child process from regaining write access to
// a read-only copy, the OS must also provide a way to remove write
// permissions at the file descriptor level. This next section
// attempts to accomplish that.
# ifdef HAVE_MEMFD_CREATE
# ifdef XP_LINUX
# define USE_MEMFD_CREATE 1
// To create a read-only duplicate of an fd, we can use procfs; the
// same operation could restore write access, but sandboxing prevents
// child processes from accessing /proc.
//
// (Note: if this ever changes to not use /proc, also reconsider how
// and if HaveMemfd should check whether this works.)
static int DupReadOnly(int fd) {
std::string path = StringPrintf("/proc/self/fd/%d", fd);
// procfs opens probably won't EINTR, but checking for it can't hurt
return HANDLE_EINTR(open(path.c_str(), O_RDONLY | O_CLOEXEC));
}
# elif defined(__FreeBSD__)
# define USE_MEMFD_CREATE 1
// FreeBSD's Capsicum framework allows irrevocably restricting the
// operations permitted on a file descriptor.
static int DupReadOnly(int fd) {
int rofd = dup(fd);
if (rofd < 0) {
return -1;
}
cap_rights_t rights;
cap_rights_init(&rights, CAP_FSTAT, CAP_MMAP_R);
if (cap_rights_limit(rofd, &rights) < 0) {
int err = errno;
close(rofd);
errno = err;
return -1;
}
return rofd;
}
# else // unhandled OS
# warning "OS has memfd_create but no DupReadOnly implementation"
# endif // OS selection
# endif // HAVE_MEMFD_CREATE
// Runtime detection for memfd support.
static bool HaveMemfd() {
# ifdef USE_MEMFD_CREATE
static const bool kHave = [] {
mozilla::UniqueFileHandle fd(
memfd_create("mozilla-ipc-test", MFD_CLOEXEC | MFD_ALLOW_SEALING));
if (!fd) {
DCHECK_EQ(errno, ENOSYS);
return false;
}
// Verify that DupReadOnly works; on Linux it's known to fail if:
//
// * SELinux assigns the memfd a type for which this process's
// domain doesn't have "open" permission; this is always the
// case on Android but could occur on desktop as well
//
// * /proc (used by the DupReadOnly implementation) isn't mounted,
// which is a configuration that the Tor Browser project is
// interested in as a way to reduce fingerprinting risk
//
// Sandboxed processes on Linux also can't use it if sandboxing
// has already been started, but that's expected. It should be
// safe for sandboxed child processes to use memfd even if an
// unsandboxed process couldn't freeze them, because freezing
// isn't allowed (or meaningful) for memory created by another
// process.
if (!PR_GetEnv("MOZ_SANDBOXED")) {
mozilla::UniqueFileHandle rofd(DupReadOnly(fd.get()));
if (!rofd) {
CHROMIUM_LOG(WARNING) << "read-only dup failed (" << strerror(errno)
<< "); not using memfd";
return false;
}
}
return true;
}();
return kHave;
# else
return false;
# endif // USE_MEMFD_CREATE
}
// static
bool SharedMemory::AppendPosixShmPrefix(std::string* str, pid_t pid) {
if (HaveMemfd()) {
return false;
}
// See also UsingPosixShm().
if (!str) {
return true;
}
*str += '/';
# ifdef MOZ_WIDGET_GTK
// The Snap package environment doesn't provide a private /dev/shm
// (it's used for communication with services like PulseAudio);
// instead AppArmor is used to restrict access to it. Anything with
// this prefix is allowed:
if (const char* snap = mozilla::widget::GetSnapInstanceName()) {
StringAppendF(str, "snap.%s.", snap);
}
# endif // XP_LINUX
// Hopefully the "implementation defined" name length limit is long
// enough for this.
StringAppendF(str, "org.mozilla.ipc.%d.", static_cast<int>(pid));
return true;
}
bool SharedMemory::CreateInternal(size_t size, bool freezeable) {
read_only_ = false;
DCHECK(size > 0);
DCHECK(!mapped_file_);
DCHECK(!frozen_file_);
mozilla::UniqueFileHandle fd;
mozilla::UniqueFileHandle frozen_fd;
bool is_memfd = false;
# ifdef USE_MEMFD_CREATE
if (HaveMemfd()) {
const unsigned flags = MFD_CLOEXEC | (freezeable ? MFD_ALLOW_SEALING : 0);
fd.reset(memfd_create("mozilla-ipc", flags));
if (!fd) {
// In general it's too late to fall back here -- in a sandboxed
// child process, shm_open is already blocked. And it shouldn't
// be necessary.
CHROMIUM_LOG(WARNING) << "failed to create memfd: " << strerror(errno);
return false;
}
is_memfd = true;
if (freezeable) {
frozen_fd.reset(DupReadOnly(fd.get()));
if (!frozen_fd) {
CHROMIUM_LOG(WARNING)
<< "failed to create read-only memfd: " << strerror(errno);
return false;
}
}
}
# endif
if (!fd) {
// Generic Unix: shm_open + shm_unlink
do {
// The names don't need to be unique, but it saves time if they
// usually are.
static mozilla::Atomic<size_t> sNameCounter;
std::string name;
CHECK(AppendPosixShmPrefix(&name, getpid()));
StringAppendF(&name, "%zu", sNameCounter++);
// O_EXCL means the names being predictable shouldn't be a problem.
fd.reset(HANDLE_EINTR(
shm_open(name.c_str(), O_RDWR | O_CREAT | O_EXCL, 0600)));
if (fd) {
if (freezeable) {
frozen_fd.reset(HANDLE_EINTR(shm_open(name.c_str(), O_RDONLY, 0400)));
if (!frozen_fd) {
int open_err = errno;
shm_unlink(name.c_str());
DLOG(FATAL) << "failed to re-open freezeable shm: "
<< strerror(open_err);
return false;
}
}
if (shm_unlink(name.c_str()) != 0) {
// This shouldn't happen, but if it does: assume the file is
// in fact leaked, and bail out now while it's still 0-length.
DLOG(FATAL) << "failed to unlink shm: " << strerror(errno);
return false;
}
}
} while (!fd && errno == EEXIST);
}
if (!fd) {
CHROMIUM_LOG(WARNING) << "failed to open shm: " << strerror(errno);
return false;
}
mozilla::Maybe<int> fallocateError;
# if defined(HAVE_POSIX_FALLOCATE)
// Using posix_fallocate will ensure that there's actually space for this
// file. Otherwise we end up with a sparse file that can give SIGBUS if we
// run out of space while writing to it. (This doesn't apply to memfd.)
if (!is_memfd) {
int rv;
// Avoid repeated interruptions of posix_fallocate by the profiler's
// SIGPROF sampling signal. Indicating "thread sleep" here means we'll
// This has to be scoped outside the HANDLE_RV_EINTR retry loop.
{
AUTO_PROFILER_THREAD_SLEEP;
rv = HANDLE_RV_EINTR(
posix_fallocate(fd.get(), 0, static_cast<off_t>(size)));
}
// Some filesystems have trouble with posix_fallocate. For now, we must
// fallback ftruncate and accept the allocation failures like we do
// without posix_fallocate.
if (rv != 0 && rv != EOPNOTSUPP && rv != EINVAL && rv != ENODEV) {
CHROMIUM_LOG(WARNING)
<< "fallocate failed to set shm size: " << strerror(rv);
return false;
}
fallocateError = mozilla::Some(rv);
}
# endif
// If posix_fallocate isn't supported / relevant for this type of
// file (either failed with an expected error, or wasn't attempted),
// then set the size with ftruncate:
if (fallocateError != mozilla::Some(0)) {
int rv = HANDLE_EINTR(ftruncate(fd.get(), static_cast<off_t>(size)));
if (rv != 0) {
int ftruncate_errno = errno;
if (fallocateError) {
CHROMIUM_LOG(WARNING) << "fallocate failed to set shm size: "
<< strerror(*fallocateError);
}
CHROMIUM_LOG(WARNING)
<< "ftruncate failed to set shm size: " << strerror(ftruncate_errno);
return false;
}
}
mapped_file_ = std::move(fd);
frozen_file_ = std::move(frozen_fd);
max_size_ = size;
freezeable_ = freezeable;
is_memfd_ = is_memfd;
return true;
}
bool SharedMemory::ReadOnlyCopy(SharedMemory* ro_out) {
DCHECK(mapped_file_);
DCHECK(!read_only_);
CHECK(freezeable_);
if (ro_out == this) {
DCHECK(!memory_);
}
# ifdef USE_MEMFD_CREATE
# ifdef MOZ_VALGRIND
// Valgrind allows memfd_create but doesn't understand F_ADD_SEALS.
static const bool haveSeals = RUNNING_ON_VALGRIND == 0;
# else
static const bool haveSeals = true;
# endif
static const bool useSeals = !PR_GetEnv("MOZ_SHM_NO_SEALS");
if (is_memfd_ && haveSeals && useSeals) {
// Seals are added to the file as defense-in-depth. The primary
// method of access control is creating a read-only fd (using
// procfs in this case) and requiring that sandboxes processes not
// have access to /proc/self/fd to regain write permission; this
// is the same as with shm_open.
//
// Unfortunately, F_SEAL_WRITE is unreliable: if the process
// forked while there was a writeable mapping, it will inherit a
// copy of the mapping, which causes the seal to fail.
//
// (Also, in the future we may want to split this into separate
// classes for mappings and shared memory handles, which would
// complicate identifying the case where `F_SEAL_WRITE` would be
// possible even in the absence of races with fork.)
//
// However, Linux 5.1 added F_SEAL_FUTURE_WRITE, which prevents
// write operations afterwards, but existing writeable mappings
// are unaffected (similar to ashmem protection semantics).
const int seals = F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL;
int sealError = EINVAL;
# ifdef F_SEAL_FUTURE_WRITE
sealError =
fcntl(mapped_file_.get(), F_ADD_SEALS, seals | F_SEAL_FUTURE_WRITE) == 0
? 0
: errno;
# endif // F_SEAL_FUTURE_WRITE
if (sealError == EINVAL) {
sealError =
fcntl(mapped_file_.get(), F_ADD_SEALS, seals) == 0 ? 0 : errno;
}
if (sealError != 0) {
CHROMIUM_LOG(WARNING) << "failed to seal memfd: " << strerror(errno);
return false;
}
}
# else // !USE_MEMFD_CREATE
DCHECK(!is_memfd_);
# endif
DCHECK(frozen_file_);
DCHECK(mapped_file_);
mapped_file_ = nullptr;
mozilla::UniqueFileHandle ro_file = std::move(frozen_file_);
DCHECK(ro_file);
freezeable_ = false;
ro_out->Close();
ro_out->mapped_file_ = std::move(ro_file);
ro_out->max_size_ = max_size_;
ro_out->read_only_ = true;
ro_out->freezeable_ = false;
return true;
}
#endif // not Android
#ifndef MAP_NORESERVE
# define MAP_NORESERVE 0
#endif
bool SharedMemory::Map(size_t bytes, void* fixed_address) {
if (!mapped_file_) {
return false;
}
DCHECK(!memory_);
// Don't use MAP_FIXED when a fixed_address was specified, since that can
// replace pages that are alread mapped at that address.
void* mem =
mmap(fixed_address, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
MAP_SHARED, mapped_file_.get(), 0);
if (mem == MAP_FAILED) {
CHROMIUM_LOG(WARNING) << "Call to mmap failed: " << strerror(errno);
return false;
}
if (fixed_address && mem != fixed_address) {
bool munmap_succeeded = munmap(mem, bytes) == 0;
DCHECK(munmap_succeeded) << "Call to munmap failed, errno=" << errno;
return false;
}
memory_ = UniqueMapping(mem, MappingDeleter(bytes));
return true;
}
void* SharedMemory::FindFreeAddressSpace(size_t size) {
void* memory = mmap(nullptr, size, PROT_NONE,
MAP_ANONYMOUS | MAP_NORESERVE | MAP_PRIVATE, -1, 0);
if (memory == MAP_FAILED) {
return nullptr;
}
munmap(memory, size);
return memory;
}
SharedMemoryHandle SharedMemory::CloneHandle() {
freezeable_ = false;
const int new_fd = dup(mapped_file_.get());
if (new_fd < 0) {
CHROMIUM_LOG(WARNING) << "failed to duplicate file descriptor: "
<< strerror(errno);
return nullptr;
}
return mozilla::UniqueFileHandle(new_fd);
}
void SharedMemory::Close(bool unmap_view) {
if (unmap_view) {
Unmap();
}
mapped_file_ = nullptr;
#ifndef ANDROID
if (frozen_file_) {
CHROMIUM_LOG(WARNING) << "freezeable shared memory was never frozen";
frozen_file_ = nullptr;
}
#endif
}
} // namespace base