1 /* $Id: port-linux.c,v 1.17 2012/03/08 23:25:18 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 */ 46 int 47 ssh_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 */ 60 static security_context_t 61 ssh_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 if (sename != NULL) 100 xfree(sename); 101 if (lvl != NULL) 102 xfree(lvl); 103 #endif 104 105 return sc; 106 } 107 108 /* Set the execution context to the default for the specified user */ 109 void 110 ssh_selinux_setup_exec_context(char *pwname) 111 { 112 security_context_t user_ctx = NULL; 113 114 if (!ssh_selinux_enabled()) 115 return; 116 117 debug3("%s: setting execution context", __func__); 118 119 user_ctx = ssh_selinux_getctxbyname(pwname); 120 if (setexeccon(user_ctx) != 0) { 121 switch (security_getenforce()) { 122 case -1: 123 fatal("%s: security_getenforce() failed", __func__); 124 case 0: 125 error("%s: Failed to set SELinux execution " 126 "context for %s", __func__, pwname); 127 break; 128 default: 129 fatal("%s: Failed to set SELinux execution context " 130 "for %s (in enforcing mode)", __func__, pwname); 131 } 132 } 133 if (user_ctx != NULL) 134 freecon(user_ctx); 135 136 debug3("%s: done", __func__); 137 } 138 139 /* Set the TTY context for the specified user */ 140 void 141 ssh_selinux_setup_pty(char *pwname, const char *tty) 142 { 143 security_context_t new_tty_ctx = NULL; 144 security_context_t user_ctx = NULL; 145 security_context_t old_tty_ctx = NULL; 146 147 if (!ssh_selinux_enabled()) 148 return; 149 150 debug3("%s: setting TTY context on %s", __func__, tty); 151 152 user_ctx = ssh_selinux_getctxbyname(pwname); 153 154 /* XXX: should these calls fatal() upon failure in enforcing mode? */ 155 156 if (getfilecon(tty, &old_tty_ctx) == -1) { 157 error("%s: getfilecon: %s", __func__, strerror(errno)); 158 goto out; 159 } 160 161 if (security_compute_relabel(user_ctx, old_tty_ctx, 162 SECCLASS_CHR_FILE, &new_tty_ctx) != 0) { 163 error("%s: security_compute_relabel: %s", 164 __func__, strerror(errno)); 165 goto out; 166 } 167 168 if (setfilecon(tty, new_tty_ctx) != 0) 169 error("%s: setfilecon: %s", __func__, strerror(errno)); 170 out: 171 if (new_tty_ctx != NULL) 172 freecon(new_tty_ctx); 173 if (old_tty_ctx != NULL) 174 freecon(old_tty_ctx); 175 if (user_ctx != NULL) 176 freecon(user_ctx); 177 debug3("%s: done", __func__); 178 } 179 180 void 181 ssh_selinux_change_context(const char *newname) 182 { 183 int len, newlen; 184 char *oldctx, *newctx, *cx; 185 void (*switchlog) (const char *fmt,...) = logit; 186 187 if (!ssh_selinux_enabled()) 188 return; 189 190 if (getcon((security_context_t *)&oldctx) < 0) { 191 logit("%s: getcon failed with %s", __func__, strerror(errno)); 192 return; 193 } 194 if ((cx = index(oldctx, ':')) == NULL || (cx = index(cx + 1, ':')) == 195 NULL) { 196 logit ("%s: unparseable context %s", __func__, oldctx); 197 return; 198 } 199 200 /* 201 * Check whether we are attempting to switch away from an unconfined 202 * security context. 203 */ 204 if (strncmp(cx, SSH_SELINUX_UNCONFINED_TYPE, 205 sizeof(SSH_SELINUX_UNCONFINED_TYPE) - 1) == 0) 206 switchlog = debug3; 207 208 newlen = strlen(oldctx) + strlen(newname) + 1; 209 newctx = xmalloc(newlen); 210 len = cx - oldctx + 1; 211 memcpy(newctx, oldctx, len); 212 strlcpy(newctx + len, newname, newlen - len); 213 if ((cx = index(cx + 1, ':'))) 214 strlcat(newctx, cx, newlen); 215 debug3("%s: setting context from '%s' to '%s'", __func__, 216 oldctx, newctx); 217 if (setcon(newctx) < 0) 218 switchlog("%s: setcon %s from %s failed with %s", __func__, 219 newctx, oldctx, strerror(errno)); 220 xfree(oldctx); 221 xfree(newctx); 222 } 223 224 void 225 ssh_selinux_setfscreatecon(const char *path) 226 { 227 security_context_t context; 228 229 if (!ssh_selinux_enabled()) 230 return; 231 if (path == NULL) { 232 setfscreatecon(NULL); 233 return; 234 } 235 if (matchpathcon(path, 0700, &context) == 0) 236 setfscreatecon(context); 237 } 238 239 #endif /* WITH_SELINUX */ 240 241 #ifdef LINUX_OOM_ADJUST 242 /* 243 * The magic "don't kill me" values, old and new, as documented in eg: 244 * http://lxr.linux.no/#linux+v2.6.32/Documentation/filesystems/proc.txt 245 * http://lxr.linux.no/#linux+v2.6.36/Documentation/filesystems/proc.txt 246 */ 247 248 static int oom_adj_save = INT_MIN; 249 static char *oom_adj_path = NULL; 250 struct { 251 char *path; 252 int value; 253 } oom_adjust[] = { 254 {"/proc/self/oom_score_adj", -1000}, /* kernels >= 2.6.36 */ 255 {"/proc/self/oom_adj", -17}, /* kernels <= 2.6.35 */ 256 {NULL, 0}, 257 }; 258 259 /* 260 * Tell the kernel's out-of-memory killer to avoid sshd. 261 * Returns the previous oom_adj value or zero. 262 */ 263 void 264 oom_adjust_setup(void) 265 { 266 int i, value; 267 FILE *fp; 268 269 debug3("%s", __func__); 270 for (i = 0; oom_adjust[i].path != NULL; i++) { 271 oom_adj_path = oom_adjust[i].path; 272 value = oom_adjust[i].value; 273 if ((fp = fopen(oom_adj_path, "r+")) != NULL) { 274 if (fscanf(fp, "%d", &oom_adj_save) != 1) 275 verbose("error reading %s: %s", oom_adj_path, 276 strerror(errno)); 277 else { 278 rewind(fp); 279 if (fprintf(fp, "%d\n", value) <= 0) 280 verbose("error writing %s: %s", 281 oom_adj_path, strerror(errno)); 282 else 283 verbose("Set %s from %d to %d", 284 oom_adj_path, oom_adj_save, value); 285 } 286 fclose(fp); 287 return; 288 } 289 } 290 oom_adj_path = NULL; 291 } 292 293 /* Restore the saved OOM adjustment */ 294 void 295 oom_adjust_restore(void) 296 { 297 FILE *fp; 298 299 debug3("%s", __func__); 300 if (oom_adj_save == INT_MIN || oom_adj_path == NULL || 301 (fp = fopen(oom_adj_path, "w")) == NULL) 302 return; 303 304 if (fprintf(fp, "%d\n", oom_adj_save) <= 0) 305 verbose("error writing %s: %s", oom_adj_path, strerror(errno)); 306 else 307 verbose("Set %s to %d", oom_adj_path, oom_adj_save); 308 309 fclose(fp); 310 return; 311 } 312 #endif /* LINUX_OOM_ADJUST */ 313 #endif /* WITH_SELINUX || LINUX_OOM_ADJUST */ 314