port-linux.c revision 295367 
1/* $Id: port-linux.c,v 1.18 2013/06/01 22:07:32 dtucker 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 = NULL;
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			sc = NULL;
90			break;
91		default:
92			fatal("%s: Failed to get default SELinux security "
93			    "context for %s (in enforcing mode)",
94			    __func__, pwname);
95		}
96	}
97
98#ifdef HAVE_GETSEUSERBYNAME
99	free(sename);
100	free(lvl);
101#endif
102
103	return sc;
104}
105
106/* Set the execution context to the default for the specified user */
107void
108ssh_selinux_setup_exec_context(char *pwname)
109{
110	security_context_t user_ctx = NULL;
111
112	if (!ssh_selinux_enabled())
113		return;
114
115	debug3("%s: setting execution context", __func__);
116
117	user_ctx = ssh_selinux_getctxbyname(pwname);
118	if (setexeccon(user_ctx) != 0) {
119		switch (security_getenforce()) {
120		case -1:
121			fatal("%s: security_getenforce() failed", __func__);
122		case 0:
123			error("%s: Failed to set SELinux execution "
124			    "context for %s", __func__, pwname);
125			break;
126		default:
127			fatal("%s: Failed to set SELinux execution context "
128			    "for %s (in enforcing mode)", __func__, pwname);
129		}
130	}
131	if (user_ctx != NULL)
132		freecon(user_ctx);
133
134	debug3("%s: done", __func__);
135}
136
137/* Set the TTY context for the specified user */
138void
139ssh_selinux_setup_pty(char *pwname, const char *tty)
140{
141	security_context_t new_tty_ctx = NULL;
142	security_context_t user_ctx = NULL;
143	security_context_t old_tty_ctx = NULL;
144
145	if (!ssh_selinux_enabled())
146		return;
147
148	debug3("%s: setting TTY context on %s", __func__, tty);
149
150	user_ctx = ssh_selinux_getctxbyname(pwname);
151
152	/* XXX: should these calls fatal() upon failure in enforcing mode? */
153
154	if (getfilecon(tty, &old_tty_ctx) == -1) {
155		error("%s: getfilecon: %s", __func__, strerror(errno));
156		goto out;
157	}
158
159	if (security_compute_relabel(user_ctx, old_tty_ctx,
160	    SECCLASS_CHR_FILE, &new_tty_ctx) != 0) {
161		error("%s: security_compute_relabel: %s",
162		    __func__, strerror(errno));
163		goto out;
164	}
165
166	if (setfilecon(tty, new_tty_ctx) != 0)
167		error("%s: setfilecon: %s", __func__, strerror(errno));
168 out:
169	if (new_tty_ctx != NULL)
170		freecon(new_tty_ctx);
171	if (old_tty_ctx != NULL)
172		freecon(old_tty_ctx);
173	if (user_ctx != NULL)
174		freecon(user_ctx);
175	debug3("%s: done", __func__);
176}
177
178void
179ssh_selinux_change_context(const char *newname)
180{
181	int len, newlen;
182	char *oldctx, *newctx, *cx;
183	void (*switchlog) (const char *fmt,...) = logit;
184
185	if (!ssh_selinux_enabled())
186		return;
187
188	if (getcon((security_context_t *)&oldctx) < 0) {
189		logit("%s: getcon failed with %s", __func__, strerror(errno));
190		return;
191	}
192	if ((cx = index(oldctx, ':')) == NULL || (cx = index(cx + 1, ':')) ==
193	    NULL) {
194		logit ("%s: unparseable context %s", __func__, oldctx);
195		return;
196	}
197
198	/*
199	 * Check whether we are attempting to switch away from an unconfined
200	 * security context.
201	 */
202	if (strncmp(cx, SSH_SELINUX_UNCONFINED_TYPE,
203	    sizeof(SSH_SELINUX_UNCONFINED_TYPE) - 1) == 0)
204		switchlog = debug3;
205
206	newlen = strlen(oldctx) + strlen(newname) + 1;
207	newctx = xmalloc(newlen);
208	len = cx - oldctx + 1;
209	memcpy(newctx, oldctx, len);
210	strlcpy(newctx + len, newname, newlen - len);
211	if ((cx = index(cx + 1, ':')))
212		strlcat(newctx, cx, newlen);
213	debug3("%s: setting context from '%s' to '%s'", __func__,
214	    oldctx, newctx);
215	if (setcon(newctx) < 0)
216		switchlog("%s: setcon %s from %s failed with %s", __func__,
217		    newctx, oldctx, strerror(errno));
218	free(oldctx);
219	free(newctx);
220}
221
222void
223ssh_selinux_setfscreatecon(const char *path)
224{
225	security_context_t context;
226
227	if (!ssh_selinux_enabled())
228		return;
229	if (path == NULL) {
230		setfscreatecon(NULL);
231		return;
232	}
233	if (matchpathcon(path, 0700, &context) == 0)
234		setfscreatecon(context);
235}
236
237#endif /* WITH_SELINUX */
238
239#ifdef LINUX_OOM_ADJUST
240/*
241 * The magic "don't kill me" values, old and new, as documented in eg:
242 * http://lxr.linux.no/#linux+v2.6.32/Documentation/filesystems/proc.txt
243 * http://lxr.linux.no/#linux+v2.6.36/Documentation/filesystems/proc.txt
244 */
245
246static int oom_adj_save = INT_MIN;
247static char *oom_adj_path = NULL;
248struct {
249	char *path;
250	int value;
251} oom_adjust[] = {
252	{"/proc/self/oom_score_adj", -1000},	/* kernels >= 2.6.36 */
253	{"/proc/self/oom_adj", -17},		/* kernels <= 2.6.35 */
254	{NULL, 0},
255};
256
257/*
258 * Tell the kernel's out-of-memory killer to avoid sshd.
259 * Returns the previous oom_adj value or zero.
260 */
261void
262oom_adjust_setup(void)
263{
264	int i, value;
265	FILE *fp;
266
267	debug3("%s", __func__);
268	 for (i = 0; oom_adjust[i].path != NULL; i++) {
269		oom_adj_path = oom_adjust[i].path;
270		value = oom_adjust[i].value;
271		if ((fp = fopen(oom_adj_path, "r+")) != NULL) {
272			if (fscanf(fp, "%d", &oom_adj_save) != 1)
273				verbose("error reading %s: %s", oom_adj_path,
274				    strerror(errno));
275			else {
276				rewind(fp);
277				if (fprintf(fp, "%d\n", value) <= 0)
278					verbose("error writing %s: %s",
279					   oom_adj_path, strerror(errno));
280				else
281					debug("Set %s from %d to %d",
282					   oom_adj_path, oom_adj_save, value);
283			}
284			fclose(fp);
285			return;
286		}
287	}
288	oom_adj_path = NULL;
289}
290
291/* Restore the saved OOM adjustment */
292void
293oom_adjust_restore(void)
294{
295	FILE *fp;
296
297	debug3("%s", __func__);
298	if (oom_adj_save == INT_MIN || oom_adj_path == NULL ||
299	    (fp = fopen(oom_adj_path, "w")) == NULL)
300		return;
301
302	if (fprintf(fp, "%d\n", oom_adj_save) <= 0)
303		verbose("error writing %s: %s", oom_adj_path, strerror(errno));
304	else
305		debug("Set %s to %d", oom_adj_path, oom_adj_save);
306
307	fclose(fp);
308	return;
309}
310#endif /* LINUX_OOM_ADJUST */
311#endif /* WITH_SELINUX || LINUX_OOM_ADJUST */
312