port-linux.c revision 1305e95ba6ff9fa202d0818caf10405df4b0f648 
1/* $Id: port-linux.c,v 1.16 2011/08/29 06:09:57 djm Exp $ */
2
3/*
4 * Copyright (c) 2005 Daniel Walsh <dwalsh@redhat.com>
5 * Copyright (c) 2006 Damien Miller <djm@openbsd.org>
6 *
7 * Permission to use, copy, modify, and distribute this software for any
8 * purpose with or without fee is hereby granted, provided that the above
9 * copyright notice and this permission notice appear in all copies.
10 *
11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18 */
19
20/*
21 * Linux-specific portability code - just SELinux support at present
22 */
23
24#include "includes.h"
25
26#if defined(WITH_SELINUX) || defined(LINUX_OOM_ADJUST)
27#include <errno.h>
28#include <stdarg.h>
29#include <string.h>
30#include <stdio.h>
31
32#include "log.h"
33#include "xmalloc.h"
34#include "port-linux.h"
35
36#ifdef WITH_SELINUX
37#include <selinux/selinux.h>
38#include <selinux/flask.h>
39#include <selinux/get_context_list.h>
40
41#ifndef SSH_SELINUX_UNCONFINED_TYPE
42# define SSH_SELINUX_UNCONFINED_TYPE ":unconfined_t:"
43#endif
44
45/* Wrapper around is_selinux_enabled() to log its return value once only */
46int
47ssh_selinux_enabled(void)
48{
49	static int enabled = -1;
50
51	if (enabled == -1) {
52		enabled = (is_selinux_enabled() == 1);
53		debug("SELinux support %s", enabled ? "enabled" : "disabled");
54	}
55
56	return (enabled);
57}
58
59/* Return the default security context for the given username */
60static security_context_t
61ssh_selinux_getctxbyname(char *pwname)
62{
63	security_context_t sc;
64	char *sename = NULL, *lvl = NULL;
65	int r;
66
67#ifdef HAVE_GETSEUSERBYNAME
68	if (getseuserbyname(pwname, &sename, &lvl) != 0)
69		return NULL;
70#else
71	sename = pwname;
72	lvl = NULL;
73#endif
74
75#ifdef HAVE_GET_DEFAULT_CONTEXT_WITH_LEVEL
76	r = get_default_context_with_level(sename, lvl, NULL, &sc);
77#else
78	r = get_default_context(sename, NULL, &sc);
79#endif
80
81	if (r != 0) {
82		switch (security_getenforce()) {
83		case -1:
84			fatal("%s: ssh_selinux_getctxbyname: "
85			    "security_getenforce() failed", __func__);
86		case 0:
87			error("%s: Failed to get default SELinux security "
88			    "context for %s", __func__, pwname);
89			break;
90		default:
91			fatal("%s: Failed to get default SELinux security "
92			    "context for %s (in enforcing mode)",
93			    __func__, pwname);
94		}
95	}
96
97#ifdef HAVE_GETSEUSERBYNAME
98	if (sename != NULL)
99		xfree(sename);
100	if (lvl != NULL)
101		xfree(lvl);
102#endif
103
104	return (sc);
105}
106
107/* Set the execution context to the default for the specified user */
108void
109ssh_selinux_setup_exec_context(char *pwname)
110{
111	security_context_t user_ctx = NULL;
112
113	if (!ssh_selinux_enabled())
114		return;
115
116	debug3("%s: setting execution context", __func__);
117
118	user_ctx = ssh_selinux_getctxbyname(pwname);
119	if (setexeccon(user_ctx) != 0) {
120		switch (security_getenforce()) {
121		case -1:
122			fatal("%s: security_getenforce() failed", __func__);
123		case 0:
124			error("%s: Failed to set SELinux execution "
125			    "context for %s", __func__, pwname);
126			break;
127		default:
128			fatal("%s: Failed to set SELinux execution context "
129			    "for %s (in enforcing mode)", __func__, pwname);
130		}
131	}
132	if (user_ctx != NULL)
133		freecon(user_ctx);
134
135	debug3("%s: done", __func__);
136}
137
138/* Set the TTY context for the specified user */
139void
140ssh_selinux_setup_pty(char *pwname, const char *tty)
141{
142	security_context_t new_tty_ctx = NULL;
143	security_context_t user_ctx = NULL;
144	security_context_t old_tty_ctx = NULL;
145
146	if (!ssh_selinux_enabled())
147		return;
148
149	debug3("%s: setting TTY context on %s", __func__, tty);
150
151	user_ctx = ssh_selinux_getctxbyname(pwname);
152
153	/* XXX: should these calls fatal() upon failure in enforcing mode? */
154
155	if (getfilecon(tty, &old_tty_ctx) == -1) {
156		error("%s: getfilecon: %s", __func__, strerror(errno));
157		goto out;
158	}
159
160	if (security_compute_relabel(user_ctx, old_tty_ctx,
161	    SECCLASS_CHR_FILE, &new_tty_ctx) != 0) {
162		error("%s: security_compute_relabel: %s",
163		    __func__, strerror(errno));
164		goto out;
165	}
166
167	if (setfilecon(tty, new_tty_ctx) != 0)
168		error("%s: setfilecon: %s", __func__, strerror(errno));
169 out:
170	if (new_tty_ctx != NULL)
171		freecon(new_tty_ctx);
172	if (old_tty_ctx != NULL)
173		freecon(old_tty_ctx);
174	if (user_ctx != NULL)
175		freecon(user_ctx);
176	debug3("%s: done", __func__);
177}
178
179void
180ssh_selinux_change_context(const char *newname)
181{
182	int len, newlen;
183	char *oldctx, *newctx, *cx;
184	void (*switchlog) (const char *fmt,...) = logit;
185
186	if (!ssh_selinux_enabled())
187		return;
188
189	if (getcon((security_context_t *)&oldctx) < 0) {
190		logit("%s: getcon failed with %s", __func__, strerror(errno));
191		return;
192	}
193	if ((cx = index(oldctx, ':')) == NULL || (cx = index(cx + 1, ':')) ==
194	    NULL) {
195		logit ("%s: unparseable context %s", __func__, oldctx);
196		return;
197	}
198
199	/*
200	 * Check whether we are attempting to switch away from an unconfined
201	 * security context.
202	 */
203	if (strncmp(cx, SSH_SELINUX_UNCONFINED_TYPE,
204	    sizeof(SSH_SELINUX_UNCONFINED_TYPE) - 1) == 0)
205		switchlog = debug3;
206
207	newlen = strlen(oldctx) + strlen(newname) + 1;
208	newctx = xmalloc(newlen);
209	len = cx - oldctx + 1;
210	memcpy(newctx, oldctx, len);
211	strlcpy(newctx + len, newname, newlen - len);
212	if ((cx = index(cx + 1, ':')))
213		strlcat(newctx, cx, newlen);
214	debug3("%s: setting context from '%s' to '%s'", __func__,
215	    oldctx, newctx);
216	if (setcon(newctx) < 0)
217		switchlog("%s: setcon %s from %s failed with %s", __func__,
218		    newctx, oldctx, strerror(errno));
219	xfree(oldctx);
220	xfree(newctx);
221}
222
223void
224ssh_selinux_setfscreatecon(const char *path)
225{
226	security_context_t context;
227
228	if (!ssh_selinux_enabled())
229		return;
230	if (path == NULL) {
231		setfscreatecon(NULL);
232		return;
233	}
234	if (matchpathcon(path, 0700, &context) == 0)
235		setfscreatecon(context);
236}
237
238#endif /* WITH_SELINUX */
239
240#ifdef LINUX_OOM_ADJUST
241/*
242 * The magic "don't kill me" values, old and new, as documented in eg:
243 * http://lxr.linux.no/#linux+v2.6.32/Documentation/filesystems/proc.txt
244 * http://lxr.linux.no/#linux+v2.6.36/Documentation/filesystems/proc.txt
245 */
246
247static int oom_adj_save = INT_MIN;
248static char *oom_adj_path = NULL;
249struct {
250	char *path;
251	int value;
252} oom_adjust[] = {
253	{"/proc/self/oom_score_adj", -1000},	/* kernels >= 2.6.36 */
254	{"/proc/self/oom_adj", -17},		/* kernels <= 2.6.35 */
255	{NULL, 0},
256};
257
258/*
259 * Tell the kernel's out-of-memory killer to avoid sshd.
260 * Returns the previous oom_adj value or zero.
261 */
262void
263oom_adjust_setup(void)
264{
265	int i, value;
266	FILE *fp;
267
268	debug3("%s", __func__);
269	 for (i = 0; oom_adjust[i].path != NULL; i++) {
270		oom_adj_path = oom_adjust[i].path;
271		value = oom_adjust[i].value;
272		if ((fp = fopen(oom_adj_path, "r+")) != NULL) {
273			if (fscanf(fp, "%d", &oom_adj_save) != 1)
274				verbose("error reading %s: %s", oom_adj_path,
275				    strerror(errno));
276			else {
277				rewind(fp);
278				if (fprintf(fp, "%d\n", value) <= 0)
279					verbose("error writing %s: %s",
280					   oom_adj_path, strerror(errno));
281				else
282					verbose("Set %s from %d to %d",
283					   oom_adj_path, oom_adj_save, value);
284			}
285			fclose(fp);
286			return;
287		}
288	}
289	oom_adj_path = NULL;
290}
291
292/* Restore the saved OOM adjustment */
293void
294oom_adjust_restore(void)
295{
296	FILE *fp;
297
298	debug3("%s", __func__);
299	if (oom_adj_save == INT_MIN || oom_adj_path == NULL ||
300	    (fp = fopen(oom_adj_path, "w")) == NULL)
301		return;
302
303	if (fprintf(fp, "%d\n", oom_adj_save) <= 0)
304		verbose("error writing %s: %s", oom_adj_path, strerror(errno));
305	else
306		verbose("Set %s to %d", oom_adj_path, oom_adj_save);
307
308	fclose(fp);
309	return;
310}
311#endif /* LINUX_OOM_ADJUST */
312#endif /* WITH_SELINUX || LINUX_OOM_ADJUST */
313