openbsd-compat/port-linux.c

   1 /* $Id: port-linux.c,v 1.12 2011/01/25 01:16:18 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 /* Wrapper around is_selinux_enabled() to log its return value once only */
  42 int
  43 ssh_selinux_enabled(void)
  44 {
  45         static int enabled = -1;
  46
  47         if (enabled == -1) {
  48                 enabled = (is_selinux_enabled() == 1);
  49                 debug("SELinux support %s", enabled ? "enabled" : "disabled");
  50         }
  51
  52         return (enabled);
  53 }
  54
  55 /* Return the default security context for the given username */
  56 static security_context_t
  57 ssh_selinux_getctxbyname(char *pwname)
  58 {
  59         security_context_t sc;
  60         char *sename = NULL, *lvl = NULL;
  61         int r;
  62
  63 #ifdef HAVE_GETSEUSERBYNAME
  64         if (getseuserbyname(pwname, &sename, &lvl) != 0)
  65                 return NULL;
  66 #else
  67         sename = pwname;
  68         lvl = NULL;
  69 #endif
  70
  71 #ifdef HAVE_GET_DEFAULT_CONTEXT_WITH_LEVEL
  72         r = get_default_context_with_level(sename, lvl, NULL, &sc);
  73 #else
  74         r = get_default_context(sename, NULL, &sc);
  75 #endif
  76
  77         if (r != 0) {
  78                 switch (security_getenforce()) {
  79                 case -1:
  80                         fatal("%s: ssh_selinux_getctxbyname: "
  81                             "security_getenforce() failed", __func__);
  82                 case 0:
  83                         error("%s: Failed to get default SELinux security "
  84                             "context for %s", __func__, pwname);
  85                         break;
  86                 default:
  87                         fatal("%s: Failed to get default SELinux security "
  88                             "context for %s (in enforcing mode)",
  89                             __func__, pwname);
  90                 }
  91         }
  92
  93 #ifdef HAVE_GETSEUSERBYNAME
  94         if (sename != NULL)
  95                 xfree(sename);
  96         if (lvl != NULL)
  97                 xfree(lvl);
  98 #endif
  99
 100         return (sc);
 101 }
 102
 103 /* Set the execution context to the default for the specified user */
 104 void
 105 ssh_selinux_setup_exec_context(char *pwname)
 106 {
 107         security_context_t user_ctx = NULL;
 108
 109         if (!ssh_selinux_enabled())
 110                 return;
 111
 112         debug3("%s: setting execution context", __func__);
 113
 114         user_ctx = ssh_selinux_getctxbyname(pwname);
 115         if (setexeccon(user_ctx) != 0) {
 116                 switch (security_getenforce()) {
 117                 case -1:
 118                         fatal("%s: security_getenforce() failed", __func__);
 119                 case 0:
 120                         error("%s: Failed to set SELinux execution "
 121                             "context for %s", __func__, pwname);
 122                         break;
 123                 default:
 124                         fatal("%s: Failed to set SELinux execution context "
 125                             "for %s (in enforcing mode)", __func__, pwname);
 126                 }
 127         }
 128         if (user_ctx != NULL)
 129                 freecon(user_ctx);
 130
 131         debug3("%s: done", __func__);
 132 }
 133
 134 /* Set the TTY context for the specified user */
 135 void
 136 ssh_selinux_setup_pty(char *pwname, const char *tty)
 137 {
 138         security_context_t new_tty_ctx = NULL;
 139         security_context_t user_ctx = NULL;
 140         security_context_t old_tty_ctx = NULL;
 141
 142         if (!ssh_selinux_enabled())
 143                 return;
 144
 145         debug3("%s: setting TTY context on %s", __func__, tty);
 146
 147         user_ctx = ssh_selinux_getctxbyname(pwname);
 148
 149         /* XXX: should these calls fatal() upon failure in enforcing mode? */
 150
 151         if (getfilecon(tty, &old_tty_ctx) == -1) {
 152                 error("%s: getfilecon: %s", __func__, strerror(errno));
 153                 goto out;
 154         }
 155
 156         if (security_compute_relabel(user_ctx, old_tty_ctx,
 157             SECCLASS_CHR_FILE, &new_tty_ctx) != 0) {
 158                 error("%s: security_compute_relabel: %s",
 159                     __func__, strerror(errno));
 160                 goto out;
 161         }
 162
 163         if (setfilecon(tty, new_tty_ctx) != 0)
 164                 error("%s: setfilecon: %s", __func__, strerror(errno));
 165  out:
 166         if (new_tty_ctx != NULL)
 167                 freecon(new_tty_ctx);
 168         if (old_tty_ctx != NULL)
 169                 freecon(old_tty_ctx);
 170         if (user_ctx != NULL)
 171                 freecon(user_ctx);
 172         debug3("%s: done", __func__);
 173 }
 174
 175 void
 176 ssh_selinux_change_context(const char *newname)
 177 {
 178         int len, newlen;
 179         char *oldctx, *newctx, *cx;
 180
 181         if (!ssh_selinux_enabled())
 182                 return;
 183
 184         if (getcon((security_context_t *)&oldctx) < 0) {
 185                 logit("%s: getcon failed with %s", __func__, strerror (errno));
 186                 return;
 187         }
 188         if ((cx = index(oldctx, ':')) == NULL || (cx = index(cx + 1, ':')) ==
 189             NULL) {
 190                 logit ("%s: unparseable context %s", __func__, oldctx);
 191                 return;
 192         }
 193
 194         newlen = strlen(oldctx) + strlen(newname) + 1;
 195         newctx = xmalloc(newlen);
 196         len = cx - oldctx + 1;
 197         memcpy(newctx, oldctx, len);
 198         strlcpy(newctx + len, newname, newlen - len);
 199         if ((cx = index(cx + 1, ':')))
 200                 strlcat(newctx, cx, newlen);
 201         debug3("%s: setting context from '%s' to '%s'", __func__, oldctx,
 202             newctx);
 203         if (setcon(newctx) < 0)
 204                 logit("%s: setcon failed with %s", __func__, strerror (errno));
 205         xfree(oldctx);
 206         xfree(newctx);
 207 }
 208
 209 void
 210 ssh_selinux_setfscreatecon(const char *path)
 211 {
 212                 security_context_t context;
 213
 214                 if (path == NULL) {
 215                         setfscreatecon(NULL);
 216                         return;
 217                 }
 218                 matchpathcon(path, 0700, &context);
 219                 setfscreatecon(context);
 220 }
 221
 222 #endif /* WITH_SELINUX */
 223
 224 #ifdef LINUX_OOM_ADJUST
 225 /*
 226  * The magic "don't kill me" values, old and new, as documented in eg:
 227  * http://lxr.linux.no/#linux+v2.6.32/Documentation/filesystems/proc.txt
 228  * http://lxr.linux.no/#linux+v2.6.36/Documentation/filesystems/proc.txt
 229  */
 230
 231 static int oom_adj_save = INT_MIN;
 232 static char *oom_adj_path = NULL;
 233 struct {
 234         char *path;
 235         int value;
 236 } oom_adjust[] = {
 237         {"/proc/self/oom_score_adj", -1000},    /* kernels >= 2.6.36 */
 238         {"/proc/self/oom_adj", -17},            /* kernels <= 2.6.35 */
 239         {NULL, 0},
 240 };
 241
 242 /*
 243  * Tell the kernel's out-of-memory killer to avoid sshd.
 244  * Returns the previous oom_adj value or zero.
 245  */
 246 void
 247 oom_adjust_setup(void)
 248 {
 249         int i, value;
 250         FILE *fp;
 251
 252         debug3("%s", __func__);
 253          for (i = 0; oom_adjust[i].path != NULL; i++) {
 254                 oom_adj_path = oom_adjust[i].path;
 255                 value = oom_adjust[i].value;
 256                 if ((fp = fopen(oom_adj_path, "r+")) != NULL) {
 257                         if (fscanf(fp, "%d", &oom_adj_save) != 1)
 258                                 verbose("error reading %s: %s", oom_adj_path,
 259                                     strerror(errno));
 260                         else {
 261                                 rewind(fp);
 262                                 if (fprintf(fp, "%d\n", value) <= 0)
 263                                         verbose("error writing %s: %s",
 264                                            oom_adj_path, strerror(errno));
 265                                 else
 266                                         verbose("Set %s from %d to %d",
 267                                            oom_adj_path, oom_adj_save, value);
 268                         }
 269                         fclose(fp);
 270                         return;
 271                 }
 272         }
 273         oom_adj_path = NULL;
 274 }
 275
 276 /* Restore the saved OOM adjustment */
 277 void
 278 oom_adjust_restore(void)
 279 {
 280         FILE *fp;
 281
 282         debug3("%s", __func__);
 283         if (oom_adj_save == INT_MIN || oom_adj_path == NULL ||
 284             (fp = fopen(oom_adj_path, "w")) == NULL)
 285                 return;
 286
 287         if (fprintf(fp, "%d\n", oom_adj_save) <= 0)
 288                 verbose("error writing %s: %s", oom_adj_path, strerror(errno));
 289         else
 290                 verbose("Set %s to %d", oom_adj_path, oom_adj_save);
 291
 292         fclose(fp);
 293         return;
 294 }
 295 #endif /* LINUX_OOM_ADJUST */
 296 #endif /* WITH_SELINUX || LINUX_OOM_ADJUST */