kernel-ctl: cygwin compatibility compile fix
[lttng-tools.git] / src / 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
6 * it under the terms of the GNU General Public License, version 2 only,
7 * as published by the Free Software Foundation.
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
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 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/signal.h>
32
33 #include <common/error.h>
34 #include <common/compat/mman.h>
35 #include <common/compat/clone.h>
36
37 #include "runas.h"
38
39 #define RUNAS_CHILD_STACK_SIZE 10485760
40
41 #ifndef MAP_STACK
42 #define MAP_STACK 0
43 #endif
44
45 #ifdef __FreeBSD__
46 /* FreeBSD MAP_STACK always return -ENOMEM */
47 #define LTTNG_MAP_STACK 0
48 #else
49 #define LTTNG_MAP_STACK MAP_STACK
50 #endif
51
52 #ifndef MAP_GROWSDOWN
53 #define MAP_GROWSDOWN 0
54 #endif
55
56 #ifndef MAP_ANONYMOUS
57 #define MAP_ANONYMOUS MAP_ANON
58 #endif
59
60 struct run_as_data {
61 int (*cmd)(void *data);
62 void *data;
63 uid_t uid;
64 gid_t gid;
65 int retval_pipe;
66 };
67
68 struct run_as_mkdir_data {
69 const char *path;
70 mode_t mode;
71 };
72
73 struct run_as_open_data {
74 const char *path;
75 int flags;
76 mode_t mode;
77 };
78
79 /*
80 * Create recursively directory using the FULL path.
81 */
82 static
83 int _mkdir_recursive(void *_data)
84 {
85 struct run_as_mkdir_data *data = _data;
86 const char *path;
87 char *p, tmp[PATH_MAX];
88 struct stat statbuf;
89 mode_t mode;
90 size_t len;
91 int ret;
92
93 path = data->path;
94 mode = data->mode;
95
96 ret = snprintf(tmp, sizeof(tmp), "%s", path);
97 if (ret < 0) {
98 PERROR("snprintf mkdir");
99 goto error;
100 }
101
102 len = ret;
103 if (tmp[len - 1] == '/') {
104 tmp[len - 1] = 0;
105 }
106
107 for (p = tmp + 1; *p; p++) {
108 if (*p == '/') {
109 *p = 0;
110 ret = stat(tmp, &statbuf);
111 if (ret < 0) {
112 ret = mkdir(tmp, mode);
113 if (ret < 0) {
114 if (!(errno == EEXIST)) {
115 PERROR("mkdir recursive");
116 ret = -errno;
117 goto error;
118 }
119 }
120 }
121 *p = '/';
122 }
123 }
124
125 ret = mkdir(tmp, mode);
126 if (ret < 0) {
127 if (!(errno == EEXIST)) {
128 PERROR("mkdir recursive last piece");
129 ret = -errno;
130 } else {
131 ret = 0;
132 }
133 }
134
135 error:
136 return ret;
137 }
138
139 static
140 int _mkdir(void *_data)
141 {
142 struct run_as_mkdir_data *data = _data;
143 return mkdir(data->path, data->mode);
144 }
145
146 static
147 int _open(void *_data)
148 {
149 struct run_as_open_data *data = _data;
150 return open(data->path, data->flags, data->mode);
151 }
152
153 static
154 int child_run_as(void *_data)
155 {
156 struct run_as_data *data = _data;
157 size_t writelen, writeleft, index;
158 union {
159 int i;
160 char c[sizeof(int)];
161 } sendret;
162 int ret;
163
164 /*
165 * Child: it is safe to drop egid and euid while sharing the
166 * file descriptors with the parent process, since we do not
167 * drop "uid": therefore, the user we are dropping egid/euid to
168 * cannot attach to this process with, e.g. ptrace, nor map this
169 * process memory.
170 */
171 if (data->gid != getegid()) {
172 ret = setegid(data->gid);
173 if (ret < 0) {
174 PERROR("setegid");
175 return EXIT_FAILURE;
176 }
177 }
178 if (data->uid != geteuid()) {
179 ret = seteuid(data->uid);
180 if (ret < 0) {
181 PERROR("seteuid");
182 return EXIT_FAILURE;
183 }
184 }
185 /*
186 * Also set umask to 0 for mkdir executable bit.
187 */
188 umask(0);
189 sendret.i = (*data->cmd)(data->data);
190 /* send back return value */
191 writeleft = sizeof(sendret);
192 index = 0;
193 do {
194 writelen = write(data->retval_pipe, &sendret.c[index],
195 writeleft);
196 if (writelen < 0) {
197 PERROR("write");
198 return EXIT_FAILURE;
199 }
200 writeleft -= writelen;
201 index += writelen;
202 } while (writeleft > 0);
203 return EXIT_SUCCESS;
204 }
205
206 static
207 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
208 {
209 struct run_as_data run_as_data;
210 int ret = 0;
211 int status;
212 pid_t pid;
213 int retval_pipe[2];
214 ssize_t readlen, readleft, index;
215 void *child_stack;
216 union {
217 int i;
218 char c[sizeof(int)];
219 } retval;
220
221 /*
222 * If we are non-root, we can only deal with our own uid.
223 */
224 if (geteuid() != 0) {
225 if (uid != geteuid()) {
226 ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
227 uid, geteuid());
228 return -EPERM;
229 }
230 }
231
232 ret = pipe(retval_pipe);
233 if (ret < 0) {
234 PERROR("pipe");
235 retval.i = ret;
236 goto end;
237 }
238 run_as_data.data = data;
239 run_as_data.cmd = cmd;
240 run_as_data.uid = uid;
241 run_as_data.gid = gid;
242 run_as_data.retval_pipe = retval_pipe[1]; /* write end */
243 child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
244 PROT_WRITE | PROT_READ,
245 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
246 -1, 0);
247 if (child_stack == MAP_FAILED) {
248 PERROR("mmap");
249 retval.i = -ENOMEM;
250 goto close_pipe;
251 }
252 /*
253 * Pointing to the middle of the stack to support architectures
254 * where the stack grows up (HPPA).
255 */
256 pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
257 &run_as_data);
258 if (pid < 0) {
259 PERROR("clone");
260 retval.i = pid;
261 goto unmap_stack;
262 }
263 /* receive return value */
264 readleft = sizeof(retval);
265 index = 0;
266 do {
267 readlen = read(retval_pipe[0], &retval.c[index], readleft);
268 if (readlen < 0) {
269 PERROR("read");
270 ret = -1;
271 break;
272 }
273 readleft -= readlen;
274 index += readlen;
275 } while (readleft > 0);
276
277 /*
278 * Parent: wait for child to return, in which case the
279 * shared memory map will have been created.
280 */
281 pid = waitpid(pid, &status, 0);
282 if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
283 PERROR("wait");
284 retval.i = -1;
285 }
286 unmap_stack:
287 ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
288 if (ret < 0) {
289 PERROR("munmap");
290 retval.i = ret;
291 }
292 close_pipe:
293 ret = close(retval_pipe[0]);
294 if (ret) {
295 PERROR("close");
296 }
297 ret = close(retval_pipe[1]);
298 if (ret) {
299 PERROR("close");
300 }
301 end:
302 return retval.i;
303 }
304
305 /*
306 * To be used on setups where gdb has issues debugging programs using
307 * clone/rfork. Note that this is for debuging ONLY, and should not be
308 * considered secure.
309 */
310 static
311 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
312 {
313 return cmd(data);
314 }
315
316 static
317 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
318 {
319 if (!getenv("LTTNG_DEBUG_NOCLONE")) {
320 int ret;
321
322 DBG("Using run_as_clone");
323 pthread_mutex_lock(&lttng_libc_state_lock);
324 ret = run_as_clone(cmd, data, uid, gid);
325 pthread_mutex_unlock(&lttng_libc_state_lock);
326 return ret;
327 } else {
328 DBG("Using run_as_noclone");
329 return run_as_noclone(cmd, data, uid, gid);
330 }
331 }
332
333 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
334 {
335 struct run_as_mkdir_data data;
336
337 DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
338 path, mode, uid, gid);
339 data.path = path;
340 data.mode = mode;
341 return run_as(_mkdir_recursive, &data, uid, gid);
342 }
343
344 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
345 {
346 struct run_as_mkdir_data data;
347
348 DBG3("mkdir() %s with mode %d for uid %d and gid %d",
349 path, mode, uid, gid);
350 data.path = path;
351 data.mode = mode;
352 return run_as(_mkdir, &data, uid, gid);
353 }
354
355 /*
356 * Note: open_run_as is currently not working. We'd need to pass the fd
357 * opened in the child to the parent.
358 */
359 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
360 {
361 struct run_as_open_data data;
362
363 DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
364 path, flags, mode, uid, gid);
365 data.path = path;
366 data.flags = flags;
367 data.mode = mode;
368 return run_as(_open, &data, uid, gid);
369 }
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