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
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "SandboxChroot.h"
#include "SandboxLogging.h"
#include "LinuxCapabilities.h"
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "base/posix/eintr_wrapper.h"
#include "mozilla/Assertions.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/NullPtr.h"
#define MOZ_ALWAYS_ZERO(e) MOZ_ALWAYS_TRUE((e) == 0)
namespace mozilla {
SandboxChroot::SandboxChroot()
{
pthread_mutexattr_t attr;
MOZ_ALWAYS_ZERO(pthread_mutexattr_init(&attr));
MOZ_ALWAYS_ZERO(pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK));
MOZ_ALWAYS_ZERO(pthread_mutex_init(&mMutex, &attr));
MOZ_ALWAYS_ZERO(pthread_cond_init(&mWakeup, nullptr));
mCommand = NO_THREAD;
}
SandboxChroot::~SandboxChroot()
{
SendCommand(JUST_EXIT);
MOZ_ALWAYS_ZERO(pthread_mutex_destroy(&mMutex));
MOZ_ALWAYS_ZERO(pthread_cond_destroy(&mWakeup));
}
bool
SandboxChroot::SendCommand(Command aComm)
{
MOZ_ALWAYS_ZERO(pthread_mutex_lock(&mMutex));
if (mCommand == NO_THREAD) {
MOZ_RELEASE_ASSERT(aComm == JUST_EXIT);
MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
return false;
} else {
MOZ_ASSERT(mCommand == NO_COMMAND);
mCommand = aComm;
MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
MOZ_ALWAYS_ZERO(pthread_cond_signal(&mWakeup));
void *retval;
if (pthread_join(mThread, &retval) != 0 || retval != nullptr) {
MOZ_CRASH("Failed to stop privileged chroot thread");
}
MOZ_ASSERT(mCommand == NO_THREAD);
}
return true;
}
static void
AlwaysClose(int fd)
{
if (IGNORE_EINTR(close(fd)) != 0) {
SANDBOX_LOG_ERROR("close: %s", strerror(errno));
MOZ_CRASH("failed to close()");
}
}
static int
OpenDeletedDirectory()
{
// We don't need this directory to persist between invocations of
// the program (nor need it to be cleaned up if something goes wrong
// here, because mkdtemp will choose a fresh name), so /tmp as
// specified by FHS is adequate.
//
// However, this needs a filesystem where a deleted directory can
// still be used, and /tmp is sometimes not that; e.g., aufs(5),
// often used for containers, will cause the chroot() to fail with
// ESTALE (bug 1162965). So this uses /dev/shm if possible instead.
char tmpPath[] = "/tmp/mozsandbox.XXXXXX";
char shmPath[] = "/dev/shm/mozsandbox.XXXXXX";
char* path;
if (mkdtemp(shmPath)) {
path = shmPath;
} else if (mkdtemp(tmpPath)) {
path = tmpPath;
} else {
SANDBOX_LOG_ERROR("mkdtemp: %s", strerror(errno));
return -1;
}
int fd = HANDLE_EINTR(open(path, O_RDONLY | O_DIRECTORY));
if (fd < 0) {
SANDBOX_LOG_ERROR("open %s: %s", path, strerror(errno));
// Try to clean up. Shouldn't fail, but livable if it does.
DebugOnly<bool> ok = HANDLE_EINTR(rmdir(path)) == 0;
MOZ_ASSERT(ok);
return -1;
}
if (HANDLE_EINTR(rmdir(path)) != 0) {
SANDBOX_LOG_ERROR("rmdir %s: %s", path, strerror(errno));
AlwaysClose(fd);
return -1;
}
return fd;
}
bool
SandboxChroot::Prepare()
{
LinuxCapabilities caps;
if (!caps.GetCurrent() || !caps.Effective(CAP_SYS_CHROOT)) {
SANDBOX_LOG_ERROR("don't have permission to chroot");
return false;
}
mFd = OpenDeletedDirectory();
if (mFd < 0) {
SANDBOX_LOG_ERROR("failed to create empty directory for chroot");
return false;
}
MOZ_ALWAYS_ZERO(pthread_mutex_lock(&mMutex));
MOZ_ASSERT(mCommand == NO_THREAD);
if (pthread_create(&mThread, nullptr, StaticThreadMain, this) != 0) {
MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
SANDBOX_LOG_ERROR("pthread_create: %s", strerror(errno));
return false;
}
while (mCommand != NO_COMMAND) {
MOZ_ASSERT(mCommand == NO_THREAD);
MOZ_ALWAYS_ZERO(pthread_cond_wait(&mWakeup, &mMutex));
}
MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
return true;
}
void
SandboxChroot::Invoke()
{
MOZ_ALWAYS_TRUE(SendCommand(DO_CHROOT));
}
static bool
ChrootToFileDesc(int fd)
{
if (fchdir(fd) != 0) {
SANDBOX_LOG_ERROR("fchdir: %s", strerror(errno));
return false;
}
if (chroot(".") != 0) {
SANDBOX_LOG_ERROR("chroot: %s", strerror(errno));
return false;
}
return true;
}
/* static */ void*
SandboxChroot::StaticThreadMain(void* aVoidPtr)
{
static_cast<SandboxChroot*>(aVoidPtr)->ThreadMain();
return nullptr;
}
void
SandboxChroot::ThreadMain()
{
// First, drop everything that isn't CAP_SYS_CHROOT. (This code
// assumes that this thread already has effective CAP_SYS_CHROOT,
// because Prepare() checked for it before creating this thread.)
LinuxCapabilities caps;
caps.Effective(CAP_SYS_CHROOT) = true;
if (!caps.SetCurrent()) {
SANDBOX_LOG_ERROR("capset: %s", strerror(errno));
MOZ_CRASH("Can't limit chroot thread's capabilities");
}
MOZ_ALWAYS_ZERO(pthread_mutex_lock(&mMutex));
MOZ_ASSERT(mCommand == NO_THREAD);
mCommand = NO_COMMAND;
MOZ_ALWAYS_ZERO(pthread_cond_signal(&mWakeup));
while (mCommand == NO_COMMAND) {
MOZ_ALWAYS_ZERO(pthread_cond_wait(&mWakeup, &mMutex));
}
if (mCommand == DO_CHROOT) {
MOZ_ASSERT(mFd >= 0);
if (!ChrootToFileDesc(mFd)) {
MOZ_CRASH("Failed to chroot");
}
} else {
MOZ_ASSERT(mCommand == JUST_EXIT);
}
if (mFd >= 0) {
AlwaysClose(mFd);
mFd = -1;
}
mCommand = NO_THREAD;
MOZ_ALWAYS_ZERO(pthread_mutex_unlock(&mMutex));
// Drop the remaining capabilities; see note in SandboxChroot.h
// about the potential unreliability of pthread_join.
if (!LinuxCapabilities().SetCurrent()) {
MOZ_CRASH("can't drop capabilities");
}
}
} // namespace mozilla
#undef MOZ_ALWAYS_ZERO
|
