1 /*
2 * Copyright (c) 2005 Daniel Walsh <dwalsh@redhat.com>
3 * Copyright (c) 2006 Damien Miller <djm@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18 /*
19 * Linux-specific portability code - just SELinux support at present
20 */
21
22 #include "includes.h"
23
24 #if defined(WITH_SELINUX) || defined(LINUX_OOM_ADJUST)
25 #include <errno.h>
26 #include <stdarg.h>
27 #include <string.h>
28 #include <stdio.h>
29
30 #include "log.h"
31 #include "xmalloc.h"
32 #include "port-linux.h"
33
34 #ifdef WITH_SELINUX
35 #include <selinux/selinux.h>
36 #include <selinux/flask.h>
37 #include <selinux/get_context_list.h>
38
39 #ifndef SSH_SELINUX_UNCONFINED_TYPE
40 # define SSH_SELINUX_UNCONFINED_TYPE ":unconfined_t:"
41 #endif
42
43 /* Wrapper around is_selinux_enabled() to log its return value once only */
44 int
ssh_selinux_enabled(void)45 ssh_selinux_enabled(void)
46 {
47 static int enabled = -1;
48
49 if (enabled == -1) {
50 enabled = (is_selinux_enabled() == 1);
51 debug("SELinux support %s", enabled ? "enabled" : "disabled");
52 }
53
54 return (enabled);
55 }
56
57 /* Return the default security context for the given username */
58 static security_context_t
ssh_selinux_getctxbyname(char * pwname)59 ssh_selinux_getctxbyname(char *pwname)
60 {
61 security_context_t sc = NULL;
62 char *sename = NULL, *lvl = NULL;
63 int r;
64
65 #ifdef HAVE_GETSEUSERBYNAME
66 if (getseuserbyname(pwname, &sename, &lvl) != 0)
67 return NULL;
68 #else
69 sename = pwname;
70 lvl = NULL;
71 #endif
72
73 #ifdef HAVE_GET_DEFAULT_CONTEXT_WITH_LEVEL
74 r = get_default_context_with_level(sename, lvl, NULL, &sc);
75 #else
76 r = get_default_context(sename, NULL, &sc);
77 #endif
78
79 if (r != 0) {
80 switch (security_getenforce()) {
81 case -1:
82 fatal("%s: ssh_selinux_getctxbyname: "
83 "security_getenforce() failed", __func__);
84 case 0:
85 error("%s: Failed to get default SELinux security "
86 "context for %s", __func__, pwname);
87 sc = NULL;
88 break;
89 default:
90 fatal("%s: Failed to get default SELinux security "
91 "context for %s (in enforcing mode)",
92 __func__, pwname);
93 }
94 }
95
96 #ifdef HAVE_GETSEUSERBYNAME
97 free(sename);
98 free(lvl);
99 #endif
100
101 return sc;
102 }
103
104 /* Set the execution context to the default for the specified user */
105 void
ssh_selinux_setup_exec_context(char * pwname)106 ssh_selinux_setup_exec_context(char *pwname)
107 {
108 security_context_t user_ctx = NULL;
109
110 if (!ssh_selinux_enabled())
111 return;
112
113 debug3("%s: setting execution context", __func__);
114
115 user_ctx = ssh_selinux_getctxbyname(pwname);
116 if (setexeccon(user_ctx) != 0) {
117 switch (security_getenforce()) {
118 case -1:
119 fatal("%s: security_getenforce() failed", __func__);
120 case 0:
121 error("%s: Failed to set SELinux execution "
122 "context for %s", __func__, pwname);
123 break;
124 default:
125 fatal("%s: Failed to set SELinux execution context "
126 "for %s (in enforcing mode)", __func__, pwname);
127 }
128 }
129 if (user_ctx != NULL)
130 freecon(user_ctx);
131
132 debug3("%s: done", __func__);
133 }
134
135 /* Set the TTY context for the specified user */
136 void
ssh_selinux_setup_pty(char * pwname,const char * tty)137 ssh_selinux_setup_pty(char *pwname, const char *tty)
138 {
139 security_context_t new_tty_ctx = NULL;
140 security_context_t user_ctx = NULL;
141 security_context_t old_tty_ctx = NULL;
142
143 if (!ssh_selinux_enabled())
144 return;
145
146 debug3("%s: setting TTY context on %s", __func__, tty);
147
148 user_ctx = ssh_selinux_getctxbyname(pwname);
149
150 /* XXX: should these calls fatal() upon failure in enforcing mode? */
151
152 if (getfilecon(tty, &old_tty_ctx) == -1) {
153 error("%s: getfilecon: %s", __func__, strerror(errno));
154 goto out;
155 }
156
157 if (security_compute_relabel(user_ctx, old_tty_ctx,
158 SECCLASS_CHR_FILE, &new_tty_ctx) != 0) {
159 error("%s: security_compute_relabel: %s",
160 __func__, strerror(errno));
161 goto out;
162 }
163
164 if (setfilecon(tty, new_tty_ctx) != 0)
165 error("%s: setfilecon: %s", __func__, strerror(errno));
166 out:
167 if (new_tty_ctx != NULL)
168 freecon(new_tty_ctx);
169 if (old_tty_ctx != NULL)
170 freecon(old_tty_ctx);
171 if (user_ctx != NULL)
172 freecon(user_ctx);
173 debug3("%s: done", __func__);
174 }
175
176 void
ssh_selinux_change_context(const char * newname)177 ssh_selinux_change_context(const char *newname)
178 {
179 int len, newlen;
180 char *oldctx, *newctx, *cx;
181 void (*switchlog) (const char *fmt,...) = logit;
182
183 if (!ssh_selinux_enabled())
184 return;
185
186 if (getcon((security_context_t *)&oldctx) < 0) {
187 logit("%s: getcon failed with %s", __func__, strerror(errno));
188 return;
189 }
190 if ((cx = index(oldctx, ':')) == NULL || (cx = index(cx + 1, ':')) ==
191 NULL) {
192 logit ("%s: unparseable context %s", __func__, oldctx);
193 return;
194 }
195
196 /*
197 * Check whether we are attempting to switch away from an unconfined
198 * security context.
199 */
200 if (strncmp(cx, SSH_SELINUX_UNCONFINED_TYPE,
201 sizeof(SSH_SELINUX_UNCONFINED_TYPE) - 1) == 0)
202 switchlog = debug3;
203
204 newlen = strlen(oldctx) + strlen(newname) + 1;
205 newctx = xmalloc(newlen);
206 len = cx - oldctx + 1;
207 memcpy(newctx, oldctx, len);
208 strlcpy(newctx + len, newname, newlen - len);
209 if ((cx = index(cx + 1, ':')))
210 strlcat(newctx, cx, newlen);
211 debug3("%s: setting context from '%s' to '%s'", __func__,
212 oldctx, newctx);
213 if (setcon(newctx) < 0)
214 switchlog("%s: setcon %s from %s failed with %s", __func__,
215 newctx, oldctx, strerror(errno));
216 free(oldctx);
217 free(newctx);
218 }
219
220 void
ssh_selinux_setfscreatecon(const char * path)221 ssh_selinux_setfscreatecon(const char *path)
222 {
223 security_context_t context;
224
225 if (!ssh_selinux_enabled())
226 return;
227 if (path == NULL) {
228 setfscreatecon(NULL);
229 return;
230 }
231 if (matchpathcon(path, 0700, &context) == 0)
232 setfscreatecon(context);
233 }
234
235 #endif /* WITH_SELINUX */
236
237 #ifdef LINUX_OOM_ADJUST
238 /*
239 * The magic "don't kill me" values, old and new, as documented in eg:
240 * http://lxr.linux.no/#linux+v2.6.32/Documentation/filesystems/proc.txt
241 * http://lxr.linux.no/#linux+v2.6.36/Documentation/filesystems/proc.txt
242 */
243
244 static int oom_adj_save = INT_MIN;
245 static char *oom_adj_path = NULL;
246 struct {
247 char *path;
248 int value;
249 } oom_adjust[] = {
250 {"/proc/self/oom_score_adj", -1000}, /* kernels >= 2.6.36 */
251 {"/proc/self/oom_adj", -17}, /* kernels <= 2.6.35 */
252 {NULL, 0},
253 };
254
255 /*
256 * Tell the kernel's out-of-memory killer to avoid sshd.
257 * Returns the previous oom_adj value or zero.
258 */
259 void
oom_adjust_setup(void)260 oom_adjust_setup(void)
261 {
262 int i, value;
263 FILE *fp;
264
265 debug3("%s", __func__);
266 for (i = 0; oom_adjust[i].path != NULL; i++) {
267 oom_adj_path = oom_adjust[i].path;
268 value = oom_adjust[i].value;
269 if ((fp = fopen(oom_adj_path, "r+")) != NULL) {
270 if (fscanf(fp, "%d", &oom_adj_save) != 1)
271 verbose("error reading %s: %s", oom_adj_path,
272 strerror(errno));
273 else {
274 rewind(fp);
275 if (fprintf(fp, "%d\n", value) <= 0)
276 verbose("error writing %s: %s",
277 oom_adj_path, strerror(errno));
278 else
279 debug("Set %s from %d to %d",
280 oom_adj_path, oom_adj_save, value);
281 }
282 fclose(fp);
283 return;
284 }
285 }
286 oom_adj_path = NULL;
287 }
288
289 /* Restore the saved OOM adjustment */
290 void
oom_adjust_restore(void)291 oom_adjust_restore(void)
292 {
293 FILE *fp;
294
295 debug3("%s", __func__);
296 if (oom_adj_save == INT_MIN || oom_adj_path == NULL ||
297 (fp = fopen(oom_adj_path, "w")) == NULL)
298 return;
299
300 if (fprintf(fp, "%d\n", oom_adj_save) <= 0)
301 verbose("error writing %s: %s", oom_adj_path, strerror(errno));
302 else
303 debug("Set %s to %d", oom_adj_path, oom_adj_save);
304
305 fclose(fp);
306 return;
307 }
308 #endif /* LINUX_OOM_ADJUST */
309 #endif /* WITH_SELINUX || LINUX_OOM_ADJUST */
310