d75eb21027ce0ae2b7df768698d8c913bb4297ea
[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/utils.h>
35 #include <common/compat/mman.h>
36 #include <common/compat/clone.h>
37
38 #include "runas.h"
39
40 #define RUNAS_CHILD_STACK_SIZE 10485760
41
42 #ifndef MAP_STACK
43 #define MAP_STACK 0
44 #endif
45
46 #ifdef __FreeBSD__
47 /* FreeBSD MAP_STACK always return -ENOMEM */
48 #define LTTNG_MAP_STACK 0
49 #else
50 #define LTTNG_MAP_STACK MAP_STACK
51 #endif
52
53 #ifndef MAP_GROWSDOWN
54 #define MAP_GROWSDOWN 0
55 #endif
56
57 #ifndef MAP_ANONYMOUS
58 #define MAP_ANONYMOUS MAP_ANON
59 #endif
60
61 struct run_as_data {
62 int (*cmd)(void *data);
63 void *data;
64 uid_t uid;
65 gid_t gid;
66 int retval_pipe;
67 };
68
69 struct run_as_mkdir_data {
70 const char *path;
71 mode_t mode;
72 };
73
74 struct run_as_open_data {
75 const char *path;
76 int flags;
77 mode_t mode;
78 };
79
80 /*
81 * Create recursively directory using the FULL path.
82 */
83 static
84 int _mkdir_recursive(void *_data)
85 {
86 struct run_as_mkdir_data *data = _data;
87 const char *path;
88 mode_t mode;
89
90 path = data->path;
91 mode = data->mode;
92
93 return utils_mkdir_recursive(path, mode);
94 }
95
96 static
97 int _mkdir(void *_data)
98 {
99 struct run_as_mkdir_data *data = _data;
100 return mkdir(data->path, data->mode);
101 }
102
103 static
104 int _open(void *_data)
105 {
106 struct run_as_open_data *data = _data;
107 return open(data->path, data->flags, data->mode);
108 }
109
110 static
111 int child_run_as(void *_data)
112 {
113 int ret;
114 struct run_as_data *data = _data;
115 ssize_t writelen;
116 size_t writeleft, index;
117 union {
118 int i;
119 char c[sizeof(int)];
120 } sendret;
121
122 /*
123 * Child: it is safe to drop egid and euid while sharing the
124 * file descriptors with the parent process, since we do not
125 * drop "uid": therefore, the user we are dropping egid/euid to
126 * cannot attach to this process with, e.g. ptrace, nor map this
127 * process memory.
128 */
129 if (data->gid != getegid()) {
130 ret = setegid(data->gid);
131 if (ret < 0) {
132 PERROR("setegid");
133 return EXIT_FAILURE;
134 }
135 }
136 if (data->uid != geteuid()) {
137 ret = seteuid(data->uid);
138 if (ret < 0) {
139 PERROR("seteuid");
140 return EXIT_FAILURE;
141 }
142 }
143 /*
144 * Also set umask to 0 for mkdir executable bit.
145 */
146 umask(0);
147 sendret.i = (*data->cmd)(data->data);
148 /* send back return value */
149 writeleft = sizeof(sendret);
150 index = 0;
151 do {
152 do {
153 writelen = write(data->retval_pipe, &sendret.c[index],
154 writeleft);
155 } while (writelen < 0 && errno == EINTR);
156 if (writelen < 0) {
157 PERROR("write");
158 return EXIT_FAILURE;
159 }
160 writeleft -= writelen;
161 index += writelen;
162 } while (writeleft > 0);
163 return EXIT_SUCCESS;
164 }
165
166 static
167 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
168 {
169 struct run_as_data run_as_data;
170 int ret = 0;
171 int status;
172 pid_t pid;
173 int retval_pipe[2];
174 ssize_t readlen, readleft, index;
175 void *child_stack;
176 union {
177 int i;
178 char c[sizeof(int)];
179 } retval;
180
181 /*
182 * If we are non-root, we can only deal with our own uid.
183 */
184 if (geteuid() != 0) {
185 if (uid != geteuid()) {
186 ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
187 uid, geteuid());
188 return -EPERM;
189 }
190 }
191
192 ret = pipe(retval_pipe);
193 if (ret < 0) {
194 PERROR("pipe");
195 retval.i = ret;
196 goto end;
197 }
198 run_as_data.data = data;
199 run_as_data.cmd = cmd;
200 run_as_data.uid = uid;
201 run_as_data.gid = gid;
202 run_as_data.retval_pipe = retval_pipe[1]; /* write end */
203 child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
204 PROT_WRITE | PROT_READ,
205 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
206 -1, 0);
207 if (child_stack == MAP_FAILED) {
208 PERROR("mmap");
209 retval.i = -ENOMEM;
210 goto close_pipe;
211 }
212 /*
213 * Pointing to the middle of the stack to support architectures
214 * where the stack grows up (HPPA).
215 */
216 pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
217 &run_as_data);
218 if (pid < 0) {
219 PERROR("clone");
220 retval.i = pid;
221 goto unmap_stack;
222 }
223 /* receive return value */
224 readleft = sizeof(retval);
225 index = 0;
226 do {
227 readlen = read(retval_pipe[0], &retval.c[index], readleft);
228 if (readlen < 0) {
229 PERROR("read");
230 ret = -1;
231 break;
232 }
233 readleft -= readlen;
234 index += readlen;
235 } while (readleft > 0);
236
237 /*
238 * Parent: wait for child to return, in which case the
239 * shared memory map will have been created.
240 */
241 pid = waitpid(pid, &status, 0);
242 if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
243 PERROR("wait");
244 retval.i = -1;
245 }
246 unmap_stack:
247 ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
248 if (ret < 0) {
249 PERROR("munmap");
250 retval.i = ret;
251 }
252 close_pipe:
253 ret = close(retval_pipe[0]);
254 if (ret) {
255 PERROR("close");
256 }
257 ret = close(retval_pipe[1]);
258 if (ret) {
259 PERROR("close");
260 }
261 end:
262 return retval.i;
263 }
264
265 /*
266 * To be used on setups where gdb has issues debugging programs using
267 * clone/rfork. Note that this is for debuging ONLY, and should not be
268 * considered secure.
269 */
270 static
271 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
272 {
273 int ret;
274 mode_t old_mask;
275
276 old_mask = umask(0);
277 ret = cmd(data);
278 umask(old_mask);
279
280 return ret;
281 }
282
283 static
284 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
285 {
286 if (!getenv("LTTNG_DEBUG_NOCLONE")) {
287 int ret;
288
289 DBG("Using run_as_clone");
290 pthread_mutex_lock(&lttng_libc_state_lock);
291 ret = run_as_clone(cmd, data, uid, gid);
292 pthread_mutex_unlock(&lttng_libc_state_lock);
293 return ret;
294 } else {
295 DBG("Using run_as_noclone");
296 return run_as_noclone(cmd, data, uid, gid);
297 }
298 }
299
300 __attribute__((visibility("hidden")))
301 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
302 {
303 struct run_as_mkdir_data data;
304
305 DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
306 path, mode, uid, gid);
307 data.path = path;
308 data.mode = mode;
309 return run_as(_mkdir_recursive, &data, uid, gid);
310 }
311
312 __attribute__((visibility("hidden")))
313 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
314 {
315 struct run_as_mkdir_data data;
316
317 DBG3("mkdir() %s with mode %d for uid %d and gid %d",
318 path, mode, uid, gid);
319 data.path = path;
320 data.mode = mode;
321 return run_as(_mkdir, &data, uid, gid);
322 }
323
324 /*
325 * Note: open_run_as is currently not working. We'd need to pass the fd
326 * opened in the child to the parent.
327 */
328 __attribute__((visibility("hidden")))
329 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
330 {
331 struct run_as_open_data data;
332
333 DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
334 path, flags, mode, uid, gid);
335 data.path = path;
336 data.flags = flags;
337 data.mode = mode;
338 return run_as(_open, &data, uid, gid);
339 }
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