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
|
#include <libfilezilla/process.hpp>
#include <libfilezilla/util.hpp>
#include <libfilezilla/glue/unix.hpp>
#include <libfilezilla/file.hpp>
#include <libfilezilla/buffer.hpp>
#include <libfilezilla/impersonation.hpp>
#include <deque>
#include <iostream>
#include <assert.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
namespace {
// Helper function to extract a directory from argv[0] so that the
// demos can be run independent of the current working directory.
fz::native_string get_program_dir(int argc, char ** argv)
{
std::string_view path;
if (argc > 0) {
path = argv[0];
auto delim = path.find_last_of("/");
if (delim == std::string::npos) {
path = std::string_view();
}
else {
path = path.substr(0, delim + 1);
}
}
return fz::to_native(path);
}
}
int main(int argc, char *argv[])
{
if (argc == 3 && !strcmp(argv[1], "MAGIC_VALUE!")) {
std::cerr << "Child: Running with euid " << geteuid() << "\n";
int sockfd = fz::to_integral<int>(argv[2]);
// Wait until after parent has dropped its privileges
char v;
if (recv(sockfd, &v, 1, 0) != 1) {
std::cerr << "Child: Could not read from socket\n";
abort();
}
std::cerr << "Child: Opening /tmp/test.txt\n";
fz::file f;
if (!f.open("/tmp/test.txt", fz::file::writing, fz::file::empty | fz::file::current_user_only)) {
std::cerr << "Could not open /tmp/test.txt\n";
abort();
}
int fd = f.detach();
fz::buffer b;
b.append("okay\n");
while (!b.empty()) {
int error{};
std::cerr << "Child: Sending descriptor " << fd << " to parent\n";
int res = fz::send_fd(sockfd, b, fd, error);
if (res < 0) {
abort();
}
if (fd != -1) {
close(fd);
}
fd = -1;
}
return 0;
}
auto user = getenv("USER");
auto pass = getenv("PASS");
if (!user || !*user || !pass || !*pass) {
std::cerr << "Pass username and password in the USER and PASS environment variables\n";
abort();
}
std::cerr << "Parent: running with euid " << geteuid() << "\n";
if (geteuid() != 0) {
std::cerr << " Warning: Consider running as root or impersonation will fail.\n";
}
fz::impersonation_token t(user, pass);
if (!t) {
std::cerr << "Parent: Could not get token\n";
return 0;
}
int spair[2];
fz::create_socketpair(spair);
fz::process p;
auto redir = fz::process::io_redirection::none; // For demo purposes. Use redirect or closeall in actual code.
bool spawned = p.spawn(t, get_program_dir(argc, argv) + "impersonation", {"MAGIC_VALUE!", fz::to_string(spair[1])}, {spair[1]}, redir);
std::cerr << "Parent: Spawned child? " << (spawned ? "Yes\n" : "No\n");
if (!spawned) {
abort();
}
close(spair[1]);
// Drop privileges
fz::impersonation_token nobody("nobody", fz::impersonation_options::pwless);
if (!nobody) {
std::cerr << "Parent: Could not get token for \"nobody\"\n";
abort();
}
if (!fz::set_process_impersonation(nobody)) {
std::cerr << "Parent: Could not drop privileges to \"nobody\"\n";
abort();
}
else {
std::cout << "Parent: Dropped privileges, euid is now " << geteuid() << std::endl;
}
char v{};
if (send(spair[0], &v, 1, 0) != 1) {
std::cerr << "Parent: Could not write to socket\n";
abort();
}
fz::buffer b;
std::deque<int> fds;
bool success{};
while (true) {
int fd, error;
int ret = fz::read_fd(spair[0], b, fd, error);
if (ret < 0) {
abort();
}
if (fd != -1) {
fds.push_back(fd);
}
if (!ret) {
if (!success || !fds.empty()) {
std::cerr << "Parent: Premature eof on socket\n";
abort();
}
break;
}
if (b.size() > 4) {
assert(!memcmp(b.get(), "okay\n", 5));
assert(!fds.empty());
std::cerr << "Parent: Got file descriptor " << fds.front() << " from child!\n";
fz::file f(fds.front());
fds.pop_front();
auto written = f.write2("Hello world!\n", 13);
if (!written || written.value_ != 13) {
std::cerr << "Parent: Could not write to file\n";
abort();
}
std::cerr << "Parent: Wrote data to file\n";
b.consume(5);
success = true;
}
}
fz::file inaccessible("/tmp/test.txt", fz::file::reading);
assert(!inaccessible.opened());
std::cerr << "Parent: As expected, parent cannot open /tmp/test.txt\n";
return 0;
}
|
