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 (at) redhat.com> 5 * Copyright (c) 2006 Damien Miller <djm (at) 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; 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 */ 108 void 109 ssh_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 */ 139 void 140 ssh_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 } 178 179 void 180 ssh_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 } 222 223 void 224 ssh_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 */ 246 247 static int oom_adj_save = INT_MIN; 248 static char *oom_adj_path = NULL; 249 struct { 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 */ 262 void 263 oom_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 */ 293 void 294 oom_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
