1/* Capture output from a subprocess.
2 Copyright (C) 2017-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <support/subprocess.h>
20#include <support/capture_subprocess.h>
21
22#include <errno.h>
23#include <fcntl.h>
24#include <stdlib.h>
25#include <support/check.h>
26#include <support/xunistd.h>
27#include <support/xsocket.h>
28#include <support/xspawn.h>
29#include <support/support.h>
30#include <support/test-driver.h>
31
32static void
33transfer (const char *what, struct pollfd *pfd, struct xmemstream *stream)
34{
35 if (pfd->revents != 0)
36 {
37 char buf[1024];
38 ssize_t ret = TEMP_FAILURE_RETRY (read (pfd->fd, buf, sizeof (buf)));
39 if (ret < 0)
40 {
41 support_record_failure ();
42 printf (format: "error: reading from subprocess %s: %m\n", what);
43 pfd->events = 0;
44 pfd->revents = 0;
45 }
46 else if (ret == 0)
47 {
48 /* EOF reached. Stop listening. */
49 pfd->events = 0;
50 pfd->revents = 0;
51 }
52 else
53 /* Store the data just read. */
54 TEST_VERIFY (fwrite (buf, ret, 1, stream->out) == 1);
55 }
56}
57
58static void
59support_capture_poll (struct support_capture_subprocess *result,
60 struct support_subprocess *proc)
61{
62 struct pollfd fds[2] =
63 {
64 { .fd = proc->stdout_pipe[0], .events = POLLIN },
65 { .fd = proc->stderr_pipe[0], .events = POLLIN },
66 };
67
68 do
69 {
70 xpoll (fds, 2, -1);
71 transfer (what: "stdout", pfd: &fds[0], stream: &result->out);
72 transfer (what: "stderr", pfd: &fds[1], stream: &result->err);
73 }
74 while (fds[0].events != 0 || fds[1].events != 0);
75
76 xfclose_memstream (stream: &result->out);
77 xfclose_memstream (stream: &result->err);
78
79 result->status = support_process_wait (proc);
80}
81
82struct support_capture_subprocess
83support_capture_subprocess (void (*callback) (void *), void *closure)
84{
85 struct support_capture_subprocess result;
86 xopen_memstream (stream: &result.out);
87 xopen_memstream (stream: &result.err);
88
89 struct support_subprocess proc = support_subprocess (callback, closure);
90
91 support_capture_poll (result: &result, proc: &proc);
92 return result;
93}
94
95struct support_capture_subprocess
96support_capture_subprogram (const char *file, char *const argv[])
97{
98 struct support_capture_subprocess result;
99 xopen_memstream (stream: &result.out);
100 xopen_memstream (stream: &result.err);
101
102 struct support_subprocess proc = support_subprogram (file, argv);
103
104 support_capture_poll (result: &result, proc: &proc);
105 return result;
106}
107
108/* Copies the executable into a restricted directory, so that we can
109 safely make it SGID with the TARGET group ID. Then runs the
110 executable. */
111static int
112copy_and_spawn_sgid (char *child_id, gid_t gid)
113{
114 char *dirname = xasprintf (format: "%s/tst-tunables-setuid.%jd",
115 test_dir, (intmax_t) getpid ());
116 char *execname = xasprintf (format: "%s/bin", dirname);
117 int infd = -1;
118 int outfd = -1;
119 int ret = 1, status = 1;
120
121 TEST_VERIFY (mkdir (dirname, 0700) == 0);
122 if (support_record_failure_is_failed ())
123 goto err;
124
125 infd = open (file: "/proc/self/exe", O_RDONLY);
126 if (infd < 0)
127 FAIL_UNSUPPORTED ("unsupported: Cannot read binary from procfs\n");
128
129 outfd = open (file: execname, O_WRONLY | O_CREAT | O_EXCL, 0700);
130 TEST_VERIFY (outfd >= 0);
131 if (support_record_failure_is_failed ())
132 goto err;
133
134 char buf[4096];
135 for (;;)
136 {
137 ssize_t rdcount = read (fd: infd, buf: buf, nbytes: sizeof (buf));
138 TEST_VERIFY (rdcount >= 0);
139 if (support_record_failure_is_failed ())
140 goto err;
141 if (rdcount == 0)
142 break;
143 char *p = buf;
144 char *end = buf + rdcount;
145 while (p != end)
146 {
147 ssize_t wrcount = write (fd: outfd, buf: buf, n: end - p);
148 if (wrcount == 0)
149 errno = ENOSPC;
150 TEST_VERIFY (wrcount > 0);
151 if (support_record_failure_is_failed ())
152 goto err;
153 p += wrcount;
154 }
155 }
156 TEST_VERIFY (fchown (outfd, getuid (), gid) == 0);
157 if (support_record_failure_is_failed ())
158 goto err;
159 TEST_VERIFY (fchmod (outfd, 02750) == 0);
160 if (support_record_failure_is_failed ())
161 goto err;
162 TEST_VERIFY (close (outfd) == 0);
163 if (support_record_failure_is_failed ())
164 goto err;
165 TEST_VERIFY (close (infd) == 0);
166 if (support_record_failure_is_failed ())
167 goto err;
168
169 /* We have the binary, now spawn the subprocess. Avoid using
170 support_subprogram because we only want the program exit status, not the
171 contents. */
172 ret = 0;
173 infd = outfd = -1;
174
175 char * const args[] = {execname, child_id, NULL};
176
177 status = support_subprogram_wait (file: args[0], argv: args);
178
179err:
180 if (outfd >= 0)
181 close (fd: outfd);
182 if (infd >= 0)
183 close (fd: infd);
184 if (execname != NULL)
185 {
186 unlink (name: execname);
187 free (ptr: execname);
188 }
189 if (dirname != NULL)
190 {
191 rmdir (path: dirname);
192 free (ptr: dirname);
193 }
194
195 if (ret != 0)
196 FAIL_EXIT1("Failed to make sgid executable for test\n");
197
198 return status;
199}
200
201int
202support_capture_subprogram_self_sgid (char *child_id)
203{
204 gid_t target = 0;
205 const int count = 64;
206 gid_t groups[count];
207
208 /* Get a GID which is not our current GID, but is present in the
209 supplementary group list. */
210 int ret = getgroups (size: count, list: groups);
211 if (ret < 0)
212 FAIL_UNSUPPORTED("Could not get group list for user %jd\n",
213 (intmax_t) getuid ());
214
215 gid_t current = getgid ();
216 for (int i = 0; i < ret; ++i)
217 {
218 if (groups[i] != current)
219 {
220 target = groups[i];
221 break;
222 }
223 }
224
225 if (target == 0)
226 FAIL_UNSUPPORTED("Could not find a suitable GID for user %jd\n",
227 (intmax_t) getuid ());
228
229 return copy_and_spawn_sgid (child_id, gid: target);
230}
231
232void
233support_capture_subprocess_free (struct support_capture_subprocess *p)
234{
235 free (ptr: p->out.buffer);
236 free (ptr: p->err.buffer);
237}
238

source code of glibc/support/support_capture_subprocess.c