Remove CLONE_VM flag
[lttng-tools.git] / common / runas.c
1 /*
2 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
3 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
4 *
5 * This program is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License as published by the Free
7 * Software Foundation; only version 2 of the License.
8 *
9 * This program is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
12 * more details.
13 *
14 * You should have received a copy of the GNU General Public License along with
15 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
16 * Place - Suite 330, Boston, MA 02111-1307, USA.
17 */
18
19 #define _GNU_SOURCE
20 #include <errno.h>
21 #include <limits.h>
22 #include <stdio.h>
23 #include <stdlib.h>
24 #include <string.h>
25 #include <sys/wait.h>
26 #include <sys/types.h>
27 #include <sys/stat.h>
28 #include <unistd.h>
29 #include <fcntl.h>
30 #include <sched.h>
31 #include <sys/mman.h>
32
33 #include <lttngerr.h>
34
35 #define CHILD_STACK_SIZE 10485760
36
37 struct run_as_data {
38 int (*cmd)(void *data);
39 void *data;
40 uid_t uid;
41 gid_t gid;
42 int retval_pipe;
43 };
44
45 struct mkdir_data {
46 const char *path;
47 mode_t mode;
48 };
49
50 struct open_data {
51 const char *path;
52 int flags;
53 mode_t mode;
54 };
55
56 /*
57 * Create recursively directory using the FULL path.
58 */
59 static
60 int _mkdir_recursive(void *_data)
61 {
62 struct mkdir_data *data = _data;
63 const char *path;
64 char *p, tmp[PATH_MAX];
65 struct stat statbuf;
66 mode_t mode;
67 size_t len;
68 int ret;
69
70 path = data->path;
71 mode = data->mode;
72
73 ret = snprintf(tmp, sizeof(tmp), "%s", path);
74 if (ret < 0) {
75 PERROR("snprintf mkdir");
76 goto error;
77 }
78
79 len = ret;
80 if (tmp[len - 1] == '/') {
81 tmp[len - 1] = 0;
82 }
83
84 for (p = tmp + 1; *p; p++) {
85 if (*p == '/') {
86 *p = 0;
87 ret = stat(tmp, &statbuf);
88 if (ret < 0) {
89 ret = mkdir(tmp, mode);
90 if (ret < 0) {
91 if (!(errno == EEXIST)) {
92 PERROR("mkdir recursive");
93 ret = -errno;
94 goto error;
95 }
96 }
97 }
98 *p = '/';
99 }
100 }
101
102 ret = mkdir(tmp, mode);
103 if (ret < 0) {
104 if (!(errno == EEXIST)) {
105 PERROR("mkdir recursive last piece");
106 ret = -errno;
107 } else {
108 ret = 0;
109 }
110 }
111
112 error:
113 return ret;
114 }
115
116 static
117 int _mkdir(void *_data)
118 {
119 struct mkdir_data *data = _data;
120 return mkdir(data->path, data->mode);
121 }
122
123 static
124 int _open(void *_data)
125 {
126 struct open_data *data = _data;
127 return open(data->path, data->flags, data->mode);
128 }
129
130 static
131 int child_run_as(void *_data)
132 {
133 struct run_as_data *data = _data;
134 size_t writelen, writeleft, index;
135 union {
136 int i;
137 char c[sizeof(int)];
138 } sendret;
139 int ret;
140
141 /*
142 * Child: it is safe to drop egid and euid while sharing the
143 * file descriptors with the parent process, since we do not
144 * drop "uid": therefore, the user we are dropping egid/euid to
145 * cannot attach to this process with, e.g. ptrace, nor map this
146 * process memory.
147 */
148 if (data->gid != getegid()) {
149 ret = setegid(data->gid);
150 if (ret < 0) {
151 perror("setegid");
152 return EXIT_FAILURE;
153 }
154 }
155 if (data->uid != geteuid()) {
156 ret = seteuid(data->uid);
157 if (ret < 0) {
158 perror("seteuid");
159 return EXIT_FAILURE;
160 }
161 }
162 /*
163 * Also set umask to 0 for mkdir executable bit.
164 */
165 umask(0);
166 sendret.i = (*data->cmd)(data->data);
167 /* send back return value */
168 writeleft = sizeof(sendret);
169 index = 0;
170 do {
171 writelen = write(data->retval_pipe, &sendret.c[index],
172 writeleft);
173 if (writelen < 0) {
174 perror("write");
175 return EXIT_FAILURE;
176 }
177 writeleft -= writelen;
178 index += writelen;
179 } while (writeleft > 0);
180 return EXIT_SUCCESS;
181 }
182
183 static
184 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
185 {
186 struct run_as_data run_as_data;
187 int ret = 0;
188 int status;
189 pid_t pid;
190 int retval_pipe[2];
191 ssize_t readlen, readleft, index;
192 void *child_stack;
193 union {
194 int i;
195 char c[sizeof(int)];
196 } retval;
197
198 /*
199 * If we are non-root, we can only deal with our own uid.
200 */
201 if (geteuid() != 0) {
202 if (uid != geteuid()) {
203 ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
204 uid, geteuid());
205 return -EPERM;
206 }
207 }
208
209 ret = pipe(retval_pipe);
210 if (ret < 0) {
211 perror("pipe");
212 goto end;
213 }
214 run_as_data.data = data;
215 run_as_data.cmd = cmd;
216 run_as_data.uid = uid;
217 run_as_data.gid = gid;
218 run_as_data.retval_pipe = retval_pipe[1]; /* write end */
219 child_stack = mmap(NULL, CHILD_STACK_SIZE,
220 PROT_WRITE | PROT_READ,
221 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
222 -1, 0);
223 if (child_stack == MAP_FAILED) {
224 perror("mmap");
225 ret = -ENOMEM;
226 goto close_pipe;
227 }
228 /*
229 * Pointing to the middle of the stack to support architectures
230 * where the stack grows up (HPPA).
231 */
232 pid = clone(child_run_as, child_stack + (CHILD_STACK_SIZE / 2),
233 CLONE_FILES | SIGCHLD,
234 &run_as_data, NULL);
235 if (pid < 0) {
236 perror("clone");
237 ret = pid;
238 goto unmap_stack;
239 }
240 /* receive return value */
241 readleft = sizeof(retval);
242 index = 0;
243 do {
244 readlen = read(retval_pipe[0], &retval.c[index], readleft);
245 if (readlen < 0) {
246 perror("read");
247 ret = -1;
248 break;
249 }
250 readleft -= readlen;
251 index += readlen;
252 } while (readleft > 0);
253
254 /*
255 * Parent: wait for child to return, in which case the
256 * shared memory map will have been created.
257 */
258 pid = waitpid(pid, &status, 0);
259 if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
260 perror("wait");
261 ret = -1;
262 }
263 unmap_stack:
264 ret = munmap(child_stack, CHILD_STACK_SIZE);
265 if (ret < 0) {
266 perror("munmap");
267 }
268 close_pipe:
269 close(retval_pipe[0]);
270 close(retval_pipe[1]);
271 end:
272 return retval.i;
273 }
274
275 int mkdir_recursive_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
276 {
277 struct mkdir_data data;
278
279 DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
280 path, mode, uid, gid);
281 data.path = path;
282 data.mode = mode;
283 return run_as(_mkdir_recursive, &data, uid, gid);
284 }
285
286 int mkdir_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
287 {
288 struct mkdir_data data;
289
290 DBG3("mkdir() %s with mode %d for uid %d and gid %d",
291 path, mode, uid, gid);
292 data.path = path;
293 data.mode = mode;
294 return run_as(_mkdir, &data, uid, gid);
295 }
296
297 /*
298 * Note: open_run_as is currently not working. We'd need to pass the fd
299 * opened in the child to the parent.
300 */
301 int open_run_as(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
302 {
303 struct open_data data;
304
305 DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
306 path, flags, mode, uid, gid);
307 data.path = path;
308 data.flags = flags;
309 data.mode = mode;
310 return run_as(_open, &data, uid, gid);
311 }
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