Mike Lockwood | 1305e95 | 2011-12-07 08:17:59 -0800 | [diff] [blame] | 1 | /* $OpenBSD: auth-rhosts.c,v 1.44 2010/03/07 11:57:13 dtucker Exp $ */ |
| 2 | /* |
| 3 | * Author: Tatu Ylonen <ylo@cs.hut.fi> |
| 4 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 5 | * All rights reserved |
| 6 | * Rhosts authentication. This file contains code to check whether to admit |
| 7 | * the login based on rhosts authentication. This file also processes |
| 8 | * /etc/hosts.equiv. |
| 9 | * |
| 10 | * As far as I am concerned, the code I have written for this software |
| 11 | * can be used freely for any purpose. Any derived versions of this |
| 12 | * software must be clearly marked as such, and if the derived work is |
| 13 | * incompatible with the protocol description in the RFC file, it must be |
| 14 | * called by a name other than "ssh" or "Secure Shell". |
| 15 | */ |
| 16 | |
| 17 | #include "includes.h" |
| 18 | |
| 19 | #include <sys/types.h> |
| 20 | #include <sys/stat.h> |
| 21 | |
| 22 | #ifdef HAVE_NETGROUP_H |
| 23 | # include <netgroup.h> |
| 24 | #endif |
| 25 | #include <pwd.h> |
| 26 | #include <stdio.h> |
| 27 | #include <string.h> |
| 28 | #include <stdarg.h> |
| 29 | #include <fcntl.h> |
| 30 | #include <unistd.h> |
| 31 | |
| 32 | #include "packet.h" |
| 33 | #include "buffer.h" |
| 34 | #include "uidswap.h" |
| 35 | #include "pathnames.h" |
| 36 | #include "log.h" |
| 37 | #include "servconf.h" |
| 38 | #include "canohost.h" |
| 39 | #include "key.h" |
| 40 | #include "hostfile.h" |
| 41 | #include "auth.h" |
| 42 | #include "misc.h" |
| 43 | |
| 44 | /* import */ |
| 45 | extern ServerOptions options; |
| 46 | extern int use_privsep; |
| 47 | |
| 48 | /* |
| 49 | * This function processes an rhosts-style file (.rhosts, .shosts, or |
| 50 | * /etc/hosts.equiv). This returns true if authentication can be granted |
| 51 | * based on the file, and returns zero otherwise. |
| 52 | */ |
| 53 | |
| 54 | static int |
| 55 | check_rhosts_file(const char *filename, const char *hostname, |
| 56 | const char *ipaddr, const char *client_user, |
| 57 | const char *server_user) |
| 58 | { |
| 59 | FILE *f; |
| 60 | char buf[1024]; /* Must not be larger than host, user, dummy below. */ |
| 61 | int fd; |
| 62 | struct stat st; |
| 63 | |
| 64 | /* Open the .rhosts file, deny if unreadable */ |
| 65 | if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) |
| 66 | return 0; |
| 67 | if (fstat(fd, &st) == -1) { |
| 68 | close(fd); |
| 69 | return 0; |
| 70 | } |
| 71 | if (!S_ISREG(st.st_mode)) { |
| 72 | logit("User %s hosts file %s is not a regular file", |
| 73 | server_user, filename); |
| 74 | close(fd); |
| 75 | return 0; |
| 76 | } |
| 77 | unset_nonblock(fd); |
| 78 | if ((f = fdopen(fd, "r")) == NULL) { |
| 79 | close(fd); |
| 80 | return 0; |
| 81 | } |
| 82 | while (fgets(buf, sizeof(buf), f)) { |
| 83 | /* All three must be at least as big as buf to avoid overflows. */ |
| 84 | char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp; |
| 85 | int negated; |
| 86 | |
| 87 | for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) |
| 88 | ; |
| 89 | if (*cp == '#' || *cp == '\n' || !*cp) |
| 90 | continue; |
| 91 | |
| 92 | /* |
| 93 | * NO_PLUS is supported at least on OSF/1. We skip it (we |
| 94 | * don't ever support the plus syntax). |
| 95 | */ |
| 96 | if (strncmp(cp, "NO_PLUS", 7) == 0) |
| 97 | continue; |
| 98 | |
| 99 | /* |
| 100 | * This should be safe because each buffer is as big as the |
| 101 | * whole string, and thus cannot be overwritten. |
| 102 | */ |
| 103 | switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, |
| 104 | dummy)) { |
| 105 | case 0: |
| 106 | auth_debug_add("Found empty line in %.100s.", filename); |
| 107 | continue; |
| 108 | case 1: |
| 109 | /* Host name only. */ |
| 110 | strlcpy(userbuf, server_user, sizeof(userbuf)); |
| 111 | break; |
| 112 | case 2: |
| 113 | /* Got both host and user name. */ |
| 114 | break; |
| 115 | case 3: |
| 116 | auth_debug_add("Found garbage in %.100s.", filename); |
| 117 | continue; |
| 118 | default: |
| 119 | /* Weird... */ |
| 120 | continue; |
| 121 | } |
| 122 | |
| 123 | host = hostbuf; |
| 124 | user = userbuf; |
| 125 | negated = 0; |
| 126 | |
| 127 | /* Process negated host names, or positive netgroups. */ |
| 128 | if (host[0] == '-') { |
| 129 | negated = 1; |
| 130 | host++; |
| 131 | } else if (host[0] == '+') |
| 132 | host++; |
| 133 | |
| 134 | if (user[0] == '-') { |
| 135 | negated = 1; |
| 136 | user++; |
| 137 | } else if (user[0] == '+') |
| 138 | user++; |
| 139 | |
| 140 | /* Check for empty host/user names (particularly '+'). */ |
| 141 | if (!host[0] || !user[0]) { |
| 142 | /* We come here if either was '+' or '-'. */ |
| 143 | auth_debug_add("Ignoring wild host/user names in %.100s.", |
| 144 | filename); |
| 145 | continue; |
| 146 | } |
| 147 | /* Verify that host name matches. */ |
| 148 | if (host[0] == '@') { |
| 149 | if (!innetgr(host + 1, hostname, NULL, NULL) && |
| 150 | !innetgr(host + 1, ipaddr, NULL, NULL)) |
| 151 | continue; |
| 152 | } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0) |
| 153 | continue; /* Different hostname. */ |
| 154 | |
| 155 | /* Verify that user name matches. */ |
| 156 | if (user[0] == '@') { |
| 157 | if (!innetgr(user + 1, NULL, client_user, NULL)) |
| 158 | continue; |
| 159 | } else if (strcmp(user, client_user) != 0) |
| 160 | continue; /* Different username. */ |
| 161 | |
| 162 | /* Found the user and host. */ |
| 163 | fclose(f); |
| 164 | |
| 165 | /* If the entry was negated, deny access. */ |
| 166 | if (negated) { |
| 167 | auth_debug_add("Matched negative entry in %.100s.", |
| 168 | filename); |
| 169 | return 0; |
| 170 | } |
| 171 | /* Accept authentication. */ |
| 172 | return 1; |
| 173 | } |
| 174 | |
| 175 | /* Authentication using this file denied. */ |
| 176 | fclose(f); |
| 177 | return 0; |
| 178 | } |
| 179 | |
| 180 | /* |
| 181 | * Tries to authenticate the user using the .shosts or .rhosts file. Returns |
| 182 | * true if authentication succeeds. If ignore_rhosts is true, only |
| 183 | * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). |
| 184 | */ |
| 185 | |
| 186 | int |
| 187 | auth_rhosts(struct passwd *pw, const char *client_user) |
| 188 | { |
| 189 | const char *hostname, *ipaddr; |
| 190 | |
| 191 | hostname = get_canonical_hostname(options.use_dns); |
| 192 | ipaddr = get_remote_ipaddr(); |
| 193 | return auth_rhosts2(pw, client_user, hostname, ipaddr); |
| 194 | } |
| 195 | |
| 196 | static int |
| 197 | auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname, |
| 198 | const char *ipaddr) |
| 199 | { |
| 200 | char buf[1024]; |
| 201 | struct stat st; |
| 202 | static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; |
| 203 | u_int rhosts_file_index; |
| 204 | |
| 205 | debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", |
| 206 | client_user, hostname, ipaddr); |
| 207 | |
| 208 | /* Switch to the user's uid. */ |
| 209 | temporarily_use_uid(pw); |
| 210 | /* |
| 211 | * Quick check: if the user has no .shosts or .rhosts files, return |
| 212 | * failure immediately without doing costly lookups from name |
| 213 | * servers. |
| 214 | */ |
| 215 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; |
| 216 | rhosts_file_index++) { |
| 217 | /* Check users .rhosts or .shosts. */ |
| 218 | snprintf(buf, sizeof buf, "%.500s/%.100s", |
| 219 | pw->pw_dir, rhosts_files[rhosts_file_index]); |
| 220 | if (stat(buf, &st) >= 0) |
| 221 | break; |
| 222 | } |
| 223 | /* Switch back to privileged uid. */ |
| 224 | restore_uid(); |
| 225 | |
| 226 | /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */ |
| 227 | if (!rhosts_files[rhosts_file_index] && |
| 228 | stat(_PATH_RHOSTS_EQUIV, &st) < 0 && |
| 229 | stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) |
| 230 | return 0; |
| 231 | |
| 232 | /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ |
| 233 | if (pw->pw_uid != 0) { |
| 234 | if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, |
| 235 | client_user, pw->pw_name)) { |
| 236 | auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", |
| 237 | hostname, ipaddr); |
| 238 | return 1; |
| 239 | } |
| 240 | if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, |
| 241 | client_user, pw->pw_name)) { |
| 242 | auth_debug_add("Accepted for %.100s [%.100s] by %.100s.", |
| 243 | hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); |
| 244 | return 1; |
| 245 | } |
| 246 | } |
| 247 | /* |
| 248 | * Check that the home directory is owned by root or the user, and is |
| 249 | * not group or world writable. |
| 250 | */ |
| 251 | if (stat(pw->pw_dir, &st) < 0) { |
| 252 | logit("Rhosts authentication refused for %.100s: " |
| 253 | "no home directory %.200s", pw->pw_name, pw->pw_dir); |
| 254 | auth_debug_add("Rhosts authentication refused for %.100s: " |
| 255 | "no home directory %.200s", pw->pw_name, pw->pw_dir); |
| 256 | return 0; |
| 257 | } |
| 258 | if (options.strict_modes && |
| 259 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || |
| 260 | (st.st_mode & 022) != 0)) { |
| 261 | logit("Rhosts authentication refused for %.100s: " |
| 262 | "bad ownership or modes for home directory.", pw->pw_name); |
| 263 | auth_debug_add("Rhosts authentication refused for %.100s: " |
| 264 | "bad ownership or modes for home directory.", pw->pw_name); |
| 265 | return 0; |
| 266 | } |
| 267 | /* Temporarily use the user's uid. */ |
| 268 | temporarily_use_uid(pw); |
| 269 | |
| 270 | /* Check all .rhosts files (currently .shosts and .rhosts). */ |
| 271 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; |
| 272 | rhosts_file_index++) { |
| 273 | /* Check users .rhosts or .shosts. */ |
| 274 | snprintf(buf, sizeof buf, "%.500s/%.100s", |
| 275 | pw->pw_dir, rhosts_files[rhosts_file_index]); |
| 276 | if (stat(buf, &st) < 0) |
| 277 | continue; |
| 278 | |
| 279 | /* |
| 280 | * Make sure that the file is either owned by the user or by |
| 281 | * root, and make sure it is not writable by anyone but the |
| 282 | * owner. This is to help avoid novices accidentally |
| 283 | * allowing access to their account by anyone. |
| 284 | */ |
| 285 | if (options.strict_modes && |
| 286 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || |
| 287 | (st.st_mode & 022) != 0)) { |
| 288 | logit("Rhosts authentication refused for %.100s: bad modes for %.200s", |
| 289 | pw->pw_name, buf); |
| 290 | auth_debug_add("Bad file modes for %.200s", buf); |
| 291 | continue; |
| 292 | } |
| 293 | /* Check if we have been configured to ignore .rhosts and .shosts files. */ |
| 294 | if (options.ignore_rhosts) { |
| 295 | auth_debug_add("Server has been configured to ignore %.100s.", |
| 296 | rhosts_files[rhosts_file_index]); |
| 297 | continue; |
| 298 | } |
| 299 | /* Check if authentication is permitted by the file. */ |
| 300 | if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) { |
| 301 | auth_debug_add("Accepted by %.100s.", |
| 302 | rhosts_files[rhosts_file_index]); |
| 303 | /* Restore the privileged uid. */ |
| 304 | restore_uid(); |
| 305 | auth_debug_add("Accepted host %s ip %s client_user %s server_user %s", |
| 306 | hostname, ipaddr, client_user, pw->pw_name); |
| 307 | return 1; |
| 308 | } |
| 309 | } |
| 310 | |
| 311 | /* Restore the privileged uid. */ |
| 312 | restore_uid(); |
| 313 | return 0; |
| 314 | } |
| 315 | |
| 316 | int |
| 317 | auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, |
| 318 | const char *ipaddr) |
| 319 | { |
| 320 | return auth_rhosts2_raw(pw, client_user, hostname, ipaddr); |
| 321 | } |