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// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/341324165): Fix and remove.
#pragma allow_unsafe_buffers
#endif
#include "content/browser/sandbox_ipc_linux.h"
#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include "base/command_line.h"
#include "base/files/scoped_file.h"
#include "base/linux_util.h"
#include "base/logging.h"
#include "base/memory/platform_shared_memory_region.h"
#include "base/posix/eintr_wrapper.h"
#include "base/posix/unix_domain_socket.h"
#include "base/process/launch.h"
#include "base/strings/string_number_conversions.h"
#include "content/public/common/content_switches.h"
#include "sandbox/linux/services/libc_interceptor.h"
#include "sandbox/policy/linux/sandbox_linux.h"
namespace content {
const size_t kMaxSandboxIPCMessagePayloadSize = 64;
// static
SandboxIPCHandler::SandboxIPCHandler(int lifeline_fd, int browser_socket)
: lifeline_fd_(lifeline_fd), browser_socket_(browser_socket) {}
void SandboxIPCHandler::Run() {
struct pollfd pfds[2];
pfds[0].fd = lifeline_fd_;
pfds[0].events = POLLIN;
pfds[1].fd = browser_socket_;
pfds[1].events = POLLIN;
int failed_polls = 0;
for (;;) {
const int r =
HANDLE_EINTR(poll(pfds, std::size(pfds), -1 /* no timeout */));
// '0' is not a possible return value with no timeout.
DCHECK_NE(0, r);
if (r < 0) {
PLOG(WARNING) << "poll";
if (failed_polls++ == 3) {
LOG(FATAL) << "poll(2) failing. SandboxIPCHandler aborting.";
}
continue;
}
failed_polls = 0;
// The browser process will close the other end of this pipe on shutdown,
// so we should exit.
if (pfds[0].revents) {
break;
}
// If poll(2) reports an error condition in this fd,
// we assume the zygote is gone and we exit the loop.
if (pfds[1].revents & (POLLERR | POLLHUP)) {
break;
}
if (pfds[1].revents & POLLIN) {
HandleRequestFromChild(browser_socket_);
}
}
VLOG(1) << "SandboxIPCHandler stopping.";
}
void SandboxIPCHandler::HandleRequestFromChild(int fd) {
std::vector<base::ScopedFD> fds;
// A FontConfigIPC::METHOD_MATCH message could be kMaxFontFamilyLength
// bytes long (this is the largest message type).
// The size limit used to be FontConfigIPC::kMaxFontFamilyLength which was
// 2048, but we do not receive FontConfig IPC here anymore. The only payloads
// here are sandbox::policy::SandboxLinux::METHOD_MAKE_SHARED_MEMORY_SEGMENT
// and HandleLocalTime from libc_interceptor for which
// kMaxSandboxIPCMessagePayloadSize set to 64 should be plenty.
// 128 bytes padding are necessary so recvmsg() does not return MSG_TRUNC
// error for a maximum length message.
uint8_t buf[kMaxSandboxIPCMessagePayloadSize + 128];
const ssize_t len =
base::UnixDomainSocket::RecvMsg(fd, buf, sizeof(buf), &fds);
if (len == -1) {
// TODO: should send an error reply, or the sender might block forever.
if (errno == EMSGSIZE) {
NOTREACHED() << "Sandbox host message is larger than "
"kMaxSandboxIPCMessagePayloadSize";
} else {
// TODO(pbos): Consider implementing PNOTREACHED() instead of using PCHECK
// here.
PCHECK(false) << "Recvmsg failed";
}
}
if (fds.empty())
return;
base::Pickle pickle = base::Pickle::WithUnownedBuffer(
base::span(buf, base::checked_cast<size_t>(len)));
base::PickleIterator iter(pickle);
int kind;
if (!iter.ReadInt(&kind))
return;
// Give sandbox first shot at request, if it is not handled, then
// false is returned and we continue on.
if (sandbox::HandleInterceptedCall(kind, fd, iter, fds))
return;
if (kind ==
sandbox::policy::SandboxLinux::METHOD_MAKE_SHARED_MEMORY_SEGMENT) {
HandleMakeSharedMemorySegment(fd, iter, fds);
return;
}
NOTREACHED();
}
void SandboxIPCHandler::HandleMakeSharedMemorySegment(
int fd,
base::PickleIterator iter,
const std::vector<base::ScopedFD>& fds) {
uint32_t size;
if (!iter.ReadUInt32(&size))
return;
// TODO(crbug.com/41470149): executable shared memory should be removed when
// NaCl is unshipped.
bool executable;
if (!iter.ReadBool(&executable))
return;
base::ScopedFD shm_fd;
if (executable) {
shm_fd =
base::subtle::PlatformSharedMemoryRegion::ExecutableRegion::CreateFD(
size);
} else {
base::subtle::PlatformSharedMemoryRegion region =
base::subtle::PlatformSharedMemoryRegion::CreateUnsafe(size);
shm_fd = std::move(region.PassPlatformHandle().fd);
}
base::Pickle reply;
SendRendererReply(fds, reply, shm_fd.get());
// shm_fd will close the handle which is no longer needed by this process.
}
void SandboxIPCHandler::SendRendererReply(
const std::vector<base::ScopedFD>& fds,
const base::Pickle& reply,
int reply_fd) {
struct msghdr msg;
memset(&msg, 0, sizeof(msg));
struct iovec iov = {const_cast<uint8_t*>(reply.data()), reply.size()};
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
char control_buffer[CMSG_SPACE(sizeof(reply_fd))];
if (reply_fd != -1) {
struct stat st;
if (fstat(reply_fd, &st) == 0 && S_ISDIR(st.st_mode)) {
LOG(FATAL) << "Tried to send a directory descriptor over sandbox IPC";
// We must never send directory descriptors to a sandboxed process
// because they can use openat with ".." elements in the path in order
// to escape the sandbox and reach the real filesystem.
}
struct cmsghdr* cmsg;
msg.msg_control = control_buffer;
msg.msg_controllen = sizeof(control_buffer);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(reply_fd));
memcpy(CMSG_DATA(cmsg), &reply_fd, sizeof(reply_fd));
msg.msg_controllen = cmsg->cmsg_len;
}
if (HANDLE_EINTR(sendmsg(fds[0].get(), &msg, MSG_DONTWAIT)) < 0)
PLOG(ERROR) << "sendmsg";
}
SandboxIPCHandler::~SandboxIPCHandler() {
if (IGNORE_EINTR(close(lifeline_fd_)) < 0)
PLOG(ERROR) << "close";
if (IGNORE_EINTR(close(browser_socket_)) < 0)
PLOG(ERROR) << "close";
}
} // namespace content
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