lttng-sessiond: Set group permissions explicitly
[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 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 <common/error.h>
34
35 #include "runas.h"
36
37 #define RUNAS_CHILD_STACK_SIZE 10485760
38
39 #ifndef MAP_STACK
40 #define MAP_STACK 0
41 #endif
42
43 struct run_as_data {
44 int (*cmd)(void *data);
45 void *data;
46 uid_t uid;
47 gid_t gid;
48 int retval_pipe;
49 };
50
51 struct run_as_mkdir_data {
52 const char *path;
53 mode_t mode;
54 };
55
56 struct run_as_open_data {
57 const char *path;
58 int flags;
59 mode_t mode;
60 };
61
62 /*
63 * Create recursively directory using the FULL path.
64 */
65 static
66 int _mkdir_recursive(void *_data)
67 {
68 struct run_as_mkdir_data *data = _data;
69 const char *path;
70 char *p, tmp[PATH_MAX];
71 struct stat statbuf;
72 mode_t mode;
73 size_t len;
74 int ret;
75
76 path = data->path;
77 mode = data->mode;
78
79 ret = snprintf(tmp, sizeof(tmp), "%s", path);
80 if (ret < 0) {
81 PERROR("snprintf mkdir");
82 goto error;
83 }
84
85 len = ret;
86 if (tmp[len - 1] == '/') {
87 tmp[len - 1] = 0;
88 }
89
90 for (p = tmp + 1; *p; p++) {
91 if (*p == '/') {
92 *p = 0;
93 ret = stat(tmp, &statbuf);
94 if (ret < 0) {
95 ret = mkdir(tmp, mode);
96 if (ret < 0) {
97 if (!(errno == EEXIST)) {
98 PERROR("mkdir recursive");
99 ret = -errno;
100 goto error;
101 }
102 }
103 }
104 *p = '/';
105 }
106 }
107
108 ret = mkdir(tmp, mode);
109 if (ret < 0) {
110 if (!(errno == EEXIST)) {
111 PERROR("mkdir recursive last piece");
112 ret = -errno;
113 } else {
114 ret = 0;
115 }
116 }
117
118 error:
119 return ret;
120 }
121
122 static
123 int _mkdir(void *_data)
124 {
125 struct run_as_mkdir_data *data = _data;
126 return mkdir(data->path, data->mode);
127 }
128
129 static
130 int _open(void *_data)
131 {
132 struct run_as_open_data *data = _data;
133 return open(data->path, data->flags, data->mode);
134 }
135
136 static
137 int child_run_as(void *_data)
138 {
139 struct run_as_data *data = _data;
140 size_t writelen, writeleft, index;
141 union {
142 int i;
143 char c[sizeof(int)];
144 } sendret;
145 int ret;
146
147 /*
148 * Child: it is safe to drop egid and euid while sharing the
149 * file descriptors with the parent process, since we do not
150 * drop "uid": therefore, the user we are dropping egid/euid to
151 * cannot attach to this process with, e.g. ptrace, nor map this
152 * process memory.
153 */
154 if (data->gid != getegid()) {
155 ret = setegid(data->gid);
156 if (ret < 0) {
157 perror("setegid");
158 return EXIT_FAILURE;
159 }
160 }
161 if (data->uid != geteuid()) {
162 ret = seteuid(data->uid);
163 if (ret < 0) {
164 perror("seteuid");
165 return EXIT_FAILURE;
166 }
167 }
168 /*
169 * Also set umask to 0 for mkdir executable bit.
170 */
171 umask(0);
172 sendret.i = (*data->cmd)(data->data);
173 /* send back return value */
174 writeleft = sizeof(sendret);
175 index = 0;
176 do {
177 writelen = write(data->retval_pipe, &sendret.c[index],
178 writeleft);
179 if (writelen < 0) {
180 perror("write");
181 return EXIT_FAILURE;
182 }
183 writeleft -= writelen;
184 index += writelen;
185 } while (writeleft > 0);
186 return EXIT_SUCCESS;
187 }
188
189 static
190 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
191 {
192 struct run_as_data run_as_data;
193 int ret = 0;
194 int status;
195 pid_t pid;
196 int retval_pipe[2];
197 ssize_t readlen, readleft, index;
198 void *child_stack;
199 union {
200 int i;
201 char c[sizeof(int)];
202 } retval;
203
204 /*
205 * If we are non-root, we can only deal with our own uid.
206 */
207 if (geteuid() != 0) {
208 if (uid != geteuid()) {
209 ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
210 uid, geteuid());
211 return -EPERM;
212 }
213 }
214
215 ret = pipe(retval_pipe);
216 if (ret < 0) {
217 perror("pipe");
218 goto end;
219 }
220 run_as_data.data = data;
221 run_as_data.cmd = cmd;
222 run_as_data.uid = uid;
223 run_as_data.gid = gid;
224 run_as_data.retval_pipe = retval_pipe[1]; /* write end */
225 child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
226 PROT_WRITE | PROT_READ,
227 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
228 -1, 0);
229 if (child_stack == MAP_FAILED) {
230 perror("mmap");
231 ret = -ENOMEM;
232 goto close_pipe;
233 }
234 /*
235 * Pointing to the middle of the stack to support architectures
236 * where the stack grows up (HPPA).
237 */
238 pid = clone(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
239 CLONE_FILES | SIGCHLD,
240 &run_as_data, NULL);
241 if (pid < 0) {
242 perror("clone");
243 ret = pid;
244 goto unmap_stack;
245 }
246 /* receive return value */
247 readleft = sizeof(retval);
248 index = 0;
249 do {
250 readlen = read(retval_pipe[0], &retval.c[index], readleft);
251 if (readlen < 0) {
252 perror("read");
253 ret = -1;
254 break;
255 }
256 readleft -= readlen;
257 index += readlen;
258 } while (readleft > 0);
259
260 /*
261 * Parent: wait for child to return, in which case the
262 * shared memory map will have been created.
263 */
264 pid = waitpid(pid, &status, 0);
265 if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
266 perror("wait");
267 ret = -1;
268 }
269 unmap_stack:
270 ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
271 if (ret < 0) {
272 perror("munmap");
273 }
274 close_pipe:
275 close(retval_pipe[0]);
276 close(retval_pipe[1]);
277 end:
278 return retval.i;
279 }
280
281 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
282 {
283 struct run_as_mkdir_data data;
284
285 DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
286 path, mode, uid, gid);
287 data.path = path;
288 data.mode = mode;
289 return run_as(_mkdir_recursive, &data, uid, gid);
290 }
291
292 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
293 {
294 struct run_as_mkdir_data data;
295
296 DBG3("mkdir() %s with mode %d for uid %d and gid %d",
297 path, mode, uid, gid);
298 data.path = path;
299 data.mode = mode;
300 return run_as(_mkdir, &data, uid, gid);
301 }
302
303 /*
304 * Note: open_run_as is currently not working. We'd need to pass the fd
305 * opened in the child to the parent.
306 */
307 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
308 {
309 struct run_as_open_data data;
310
311 DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
312 path, flags, mode, uid, gid);
313 data.path = path;
314 data.flags = flags;
315 data.mode = mode;
316 return run_as(_open, &data, uid, gid);
317 }
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