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
|
#define _GNU_SOURCE
#include <glib.h>
#include <glib/gstdio.h>
#include <errno.h>
#include <sched.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/syscall.h>
#define fail(s, err) g_error("%s: %s: %s", __func__, s, g_strerror(err))
#define fail_if(expr) \
if (expr) \
fail(#expr, errno);
const gchar *bind_blacklist[] = {"bin", "etc", "host", "real-host", "usr", "lib", "lib64", "lib32", "sbin", NULL};
int pivot_root(const char *new_root, const char *put_old) {
return syscall(SYS_pivot_root, new_root, put_old);
}
void mount_tmpfs(const gchar *target) {
fail_if(mount("none", target, "tmpfs", 0, NULL));
}
void bind_mount(const gchar *source, const gchar *target) {
fail_if(g_mkdir(target, 0755));
fail_if(mount(source, target, NULL, MS_BIND | MS_REC, NULL));
}
const gchar *create_tmpdir() {
gchar *prefix =
g_build_filename(g_get_tmp_dir(), "chrootenvXXXXXX", NULL);
fail_if(!g_mkdtemp_full(prefix, 0755));
return prefix;
}
void pivot_host(const gchar *guest) {
g_autofree gchar *point = g_build_filename(guest, "host", NULL);
fail_if(g_mkdir(point, 0755));
fail_if(mount(0, "/", 0, MS_PRIVATE | MS_REC, 0));
fail_if(pivot_root(guest, point));
}
void bind_mount_item(const gchar *host, const gchar *guest, const gchar *name) {
g_autofree gchar *source = g_build_filename(host, name, NULL);
g_autofree gchar *target = g_build_filename(guest, name, NULL);
if (G_LIKELY(g_file_test(source, G_FILE_TEST_IS_DIR)))
bind_mount(source, target);
}
void bind(const gchar *host, const gchar *guest) {
mount_tmpfs(guest);
pivot_host(guest);
g_autofree gchar *host_dir = g_build_filename("/host", host, NULL);
g_autoptr(GError) err = NULL;
g_autoptr(GDir) dir = g_dir_open(host_dir, 0, &err);
if (err != NULL)
fail("g_dir_open", errno);
const gchar *item;
while ((item = g_dir_read_name(dir)))
if (!g_strv_contains(bind_blacklist, item))
bind_mount_item(host_dir, "/", item);
}
void spit(const char *path, char *fmt, ...) {
va_list args;
va_start(args, fmt);
FILE *f = g_fopen(path, "w");
if (f == NULL)
fail("g_fopen", errno);
g_vfprintf(f, fmt, args);
fclose(f);
}
int main(gint argc, gchar **argv) {
const gchar *self = *argv++;
if (argc < 2) {
g_message("%s command [arguments...]", self);
return 1;
}
g_autofree const gchar *prefix = create_tmpdir();
pid_t cpid = fork();
if (cpid < 0)
fail("fork", errno);
else if (cpid == 0) {
uid_t uid = getuid();
gid_t gid = getgid();
int namespaces = CLONE_NEWNS;
if (uid != 0) {
namespaces |= CLONE_NEWUSER;
}
if (unshare(namespaces) < 0) {
int unshare_errno = errno;
g_message("Requires Linux version >= 3.19 built with CONFIG_USER_NS");
if (g_file_test("/proc/sys/kernel/unprivileged_userns_clone",
G_FILE_TEST_EXISTS))
g_message("Run: sudo sysctl -w kernel.unprivileged_userns_clone=1");
fail("unshare", unshare_errno);
}
if (uid != 0) {
spit("/proc/self/setgroups", "deny");
spit("/proc/self/uid_map", "%d %d 1", uid, uid);
spit("/proc/self/gid_map", "%d %d 1", gid, gid);
}
// If there is a /host directory, assume this is nested chrootenv and use it as host instead.
gboolean nested_host = g_file_test("/host", G_FILE_TEST_EXISTS | G_FILE_TEST_IS_DIR);
g_autofree const gchar *host = nested_host ? "/host" : "/";
bind(host, prefix);
// Replace /host by an actual (inner) /host.
if (nested_host) {
fail_if(g_mkdir("/real-host", 0755));
fail_if(mount("/host/host", "/real-host", NULL, MS_BIND | MS_REC, NULL));
// For some reason umount("/host") returns EBUSY even immediately after
// pivot_root. We detach it at least to keep `/proc/mounts` from blowing
// up in nested cases.
fail_if(umount2("/host", MNT_DETACH));
fail_if(mount("/real-host", "/host", NULL, MS_MOVE, NULL));
fail_if(rmdir("/real-host"));
}
fail_if(chdir("/"));
fail_if(execvp(*argv, argv));
}
else {
int status;
fail_if(waitpid(cpid, &status, 0) != cpid);
fail_if(rmdir(prefix));
if (WIFEXITED(status))
return WEXITSTATUS(status);
else if (WIFSIGNALED(status))
kill(getpid(), WTERMSIG(status));
return 1;
}
}
|