1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
// Copyright (c) 2011 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.
// A mini-zygote specifically for Native Client.
#include "chrome/common/nacl_helper_linux.h"
#include <errno.h>
#include <link.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <string>
#include <vector>
#include "base/at_exit.h"
#include "base/command_line.h"
#include "base/eintr_wrapper.h"
#include "base/logging.h"
#include "base/message_loop.h"
#include "base/rand_util.h"
#include "chrome/nacl/nacl_listener.h"
#include "content/common/unix_domain_socket_posix.h"
#include "ipc/ipc_switches.h"
#include "native_client/src/trusted/service_runtime/sel_memory.h"
namespace {
bool g_suid_sandbox_active;
// The child must mimic the behavior of zygote_main_linux.cc on the child
// side of the fork. See zygote_main_linux.cc:HandleForkRequest from
// if (!child) {
// Note: this code doesn't attempt to support SELINUX or the SECCOMP sandbox.
void BecomeNaClLoader(const std::vector<int>& child_fds) {
VLOG(1) << "NaCl loader: setting up IPC descriptor";
// don't need zygote FD any more
if (HANDLE_EINTR(close(kNaClZygoteDescriptor)) != 0)
LOG(ERROR) << "close(kNaClZygoteDescriptor) failed.";
// Set up browser descriptor as expected by Chrome on fd 3
// The zygote takes care of putting the sandbox IPC channel on fd 5
int zfd = dup2(child_fds[kNaClBrowserFDIndex], kNaClBrowserDescriptor);
if (zfd != kNaClBrowserDescriptor) {
LOG(ERROR) << "Could not initialize kNaClBrowserDescriptor";
_exit(-1);
}
MessageLoopForIO main_message_loop;
NaClListener listener;
listener.Listen();
_exit(0);
}
// Some of this code was lifted from
// content/browser/zygote_main_linux.cc:ForkWithRealPid()
void HandleForkRequest(const std::vector<int>& child_fds) {
VLOG(1) << "nacl_helper: forking";
pid_t childpid = fork();
if (childpid < 0) {
perror("fork");
LOG(ERROR) << "*** HandleForkRequest failed\n";
// fall through to parent case below
} else if (childpid == 0) { // In the child process.
bool validack = false;
const size_t kMaxReadSize = 1024;
char buffer[kMaxReadSize];
// Wait until the parent process has discovered our PID. We
// should not fork any child processes (which the seccomp
// sandbox does) until then, because that can interfere with the
// parent's discovery of our PID.
const int nread = HANDLE_EINTR(read(child_fds[kNaClParentFDIndex], buffer,
kMaxReadSize));
const std::string switch_prefix = std::string("--") +
switches::kProcessChannelID + std::string("=");
const size_t len = switch_prefix.length();
if (nread < 0) {
perror("read");
LOG(ERROR) << "read returned " << nread;
} else if (nread > static_cast<int>(len)) {
if (switch_prefix.compare(0, len, buffer, 0, len) == 0) {
VLOG(1) << "NaCl loader is synchronised with Chrome zygote";
CommandLine::ForCurrentProcess()->AppendSwitchASCII(
switches::kProcessChannelID,
std::string(&buffer[len], nread - len));
validack = true;
}
}
if (HANDLE_EINTR(close(child_fds[kNaClDummyFDIndex])) != 0)
LOG(ERROR) << "close(child_fds[kNaClDummyFDIndex]) failed";
if (HANDLE_EINTR(close(child_fds[kNaClParentFDIndex])) != 0)
LOG(ERROR) << "close(child_fds[kNaClParentFDIndex]) failed";
if (validack) {
BecomeNaClLoader(child_fds);
} else {
LOG(ERROR) << "Failed to synch with zygote";
}
// NOTREACHED
return;
}
// I am the parent.
// First, close the dummy_fd so the sandbox won't find me when
// looking for the child's pid in /proc. Also close other fds.
for (size_t i = 0; i < child_fds.size(); i++) {
if (HANDLE_EINTR(close(child_fds[i])) != 0)
LOG(ERROR) << "close(child_fds[i]) failed";
}
VLOG(1) << "nacl_helper: childpid is " << childpid;
// Now tell childpid to the Chrome zygote.
if (HANDLE_EINTR(send(kNaClZygoteDescriptor,
&childpid, sizeof(childpid), MSG_EOR))
!= sizeof(childpid)) {
LOG(ERROR) << "*** send() to zygote failed";
}
}
} // namespace
static const char kNaClHelperAtZero[] = "at-zero";
static const char kNaClHelperRDebug[] = "r_debug";
/*
* Since we were started by the bootstrap program rather than in the
* usual way, the debugger cannot figure out where our executable
* or the dynamic linker or the shared libraries are in memory,
* so it won't find any symbols. But we can fake it out to find us.
*
* The zygote passes --r_debug=0xXXXXXXXXXXXXXXXX. The bootstrap
* program replaces the Xs with the address of its _r_debug
* structure. The debugger will look for that symbol by name to
* discover the addresses of key dynamic linker data structures.
* Since all it knows about is the original main executable, which
* is the bootstrap program, it finds the symbol defined there. The
* dynamic linker's structure is somewhere else, but it is filled in
* after initialization. The parts that really matter to the
* debugger never change. So we just copy the contents of the
* dynamic linker's structure into the address provided by the option.
* Hereafter, if someone attaches a debugger (or examines a core dump),
* the debugger will find all the symbols in the normal way.
*/
static void check_r_debug(char *argv0) {
std::string r_debug_switch_value =
CommandLine::ForCurrentProcess()->GetSwitchValueASCII(kNaClHelperRDebug);
if (!r_debug_switch_value.empty()) {
char *endp = NULL;
uintptr_t r_debug_addr = strtoul(r_debug_switch_value.c_str(), &endp, 0);
if (r_debug_addr != 0 && *endp == '\0') {
struct r_debug *bootstrap_r_debug = (struct r_debug *) r_debug_addr;
*bootstrap_r_debug = _r_debug;
/*
* Since the main executable (the bootstrap program) does not
* have a dynamic section, the debugger will not skip the
* first element of the link_map list as it usually would for
* an executable or PIE that was loaded normally. But the
* dynamic linker has set l_name for the PIE to "" as is
* normal for the main executable. So the debugger doesn't
* know which file it is. Fill in the actual file name, which
* came in as our argv[0].
*/
struct link_map *l = _r_debug.r_map;
if (l->l_name[0] == '\0')
l->l_name = argv0;
}
}
}
int main(int argc, char *argv[]) {
CommandLine::Init(argc, argv);
base::AtExitManager exit_manager;
base::RandUint64(); // acquire /dev/urandom fd before sandbox is raised
std::vector<int> empty; // for SendMsg() calls
check_r_debug(argv[0]);
g_suid_sandbox_active = (NULL != getenv("SBX_D"));
if (CommandLine::ForCurrentProcess()->HasSwitch(kNaClHelperAtZero)) {
g_nacl_prereserved_sandbox_addr = (void *) (uintptr_t) 0x10000;
}
// Send the zygote a message to let it know we are ready to help
if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor,
kNaClHelperStartupAck,
sizeof(kNaClHelperStartupAck), empty)) {
LOG(ERROR) << "*** send() to zygote failed";
}
while (true) {
int badpid = -1;
std::vector<int> fds;
static const unsigned kMaxMessageLength = 2048;
char buf[kMaxMessageLength];
const ssize_t msglen = UnixDomainSocket::RecvMsg(kNaClZygoteDescriptor,
&buf, sizeof(buf), &fds);
if (msglen == 0 || (msglen == -1 && errno == ECONNRESET)) {
// EOF from the browser. Goodbye!
_exit(0);
}
if (msglen == sizeof(kNaClForkRequest) - 1 &&
memcmp(buf, kNaClForkRequest, msglen) == 0) {
if (kNaClParentFDIndex + 1 == fds.size()) {
HandleForkRequest(fds);
continue; // fork succeeded. Note: child does not return
} else {
LOG(ERROR) << "nacl_helper: unexpected number of fds, got "
<< fds.size();
}
} else {
if (msglen != 0) {
LOG(ERROR) << "nacl_helper unrecognized request: %s";
_exit(-1);
}
}
// if fork fails, send PID=-1 to zygote
if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid,
sizeof(badpid), empty)) {
LOG(ERROR) << "*** send() to zygote failed";
}
}
CHECK(false); // This routine must not return
}
|
