1 /* $OpenBSD: auth-rhosts.c,v 1.46 2014/12/23 22:42:48 djm Exp $ */ 2 /* 3 * Author: Tatu Ylonen <ylo (at) cs.hut.fi> 4 * Copyright (c) 1995 Tatu Ylonen <ylo (at) 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 "misc.h" 38 #include "servconf.h" 39 #include "canohost.h" 40 #include "key.h" 41 #include "hostfile.h" 42 #include "auth.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 #define RBUFLN 1024 61 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 62 int fd; 63 struct stat st; 64 65 /* Open the .rhosts file, deny if unreadable */ 66 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 67 return 0; 68 if (fstat(fd, &st) == -1) { 69 close(fd); 70 return 0; 71 } 72 if (!S_ISREG(st.st_mode)) { 73 logit("User %s hosts file %s is not a regular file", 74 server_user, filename); 75 close(fd); 76 return 0; 77 } 78 unset_nonblock(fd); 79 if ((f = fdopen(fd, "r")) == NULL) { 80 close(fd); 81 return 0; 82 } 83 while (fgets(buf, sizeof(buf), f)) { 84 /* All three must have length >= buf to avoid overflows. */ 85 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 86 char *host, *user, *cp; 87 int negated; 88 89 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 90 ; 91 if (*cp == '#' || *cp == '\n' || !*cp) 92 continue; 93 94 /* 95 * NO_PLUS is supported at least on OSF/1. We skip it (we 96 * don't ever support the plus syntax). 97 */ 98 if (strncmp(cp, "NO_PLUS", 7) == 0) 99 continue; 100 101 /* 102 * This should be safe because each buffer is as big as the 103 * whole string, and thus cannot be overwritten. 104 */ 105 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 106 dummy)) { 107 case 0: 108 auth_debug_add("Found empty line in %.100s.", filename); 109 continue; 110 case 1: 111 /* Host name only. */ 112 strlcpy(userbuf, server_user, sizeof(userbuf)); 113 break; 114 case 2: 115 /* Got both host and user name. */ 116 break; 117 case 3: 118 auth_debug_add("Found garbage in %.100s.", filename); 119 continue; 120 default: 121 /* Weird... */ 122 continue; 123 } 124 125 host = hostbuf; 126 user = userbuf; 127 negated = 0; 128 129 /* Process negated host names, or positive netgroups. */ 130 if (host[0] == '-') { 131 negated = 1; 132 host++; 133 } else if (host[0] == '+') 134 host++; 135 136 if (user[0] == '-') { 137 negated = 1; 138 user++; 139 } else if (user[0] == '+') 140 user++; 141 142 /* Check for empty host/user names (particularly '+'). */ 143 if (!host[0] || !user[0]) { 144 /* We come here if either was '+' or '-'. */ 145 auth_debug_add("Ignoring wild host/user names " 146 "in %.100s.", filename); 147 continue; 148 } 149 /* Verify that host name matches. */ 150 if (host[0] == '@') { 151 if (!innetgr(host + 1, hostname, NULL, NULL) && 152 !innetgr(host + 1, ipaddr, NULL, NULL)) 153 continue; 154 } else if (strcasecmp(host, hostname) && 155 strcmp(host, ipaddr) != 0) 156 continue; /* Different hostname. */ 157 158 /* Verify that user name matches. */ 159 if (user[0] == '@') { 160 if (!innetgr(user + 1, NULL, client_user, NULL)) 161 continue; 162 } else if (strcmp(user, client_user) != 0) 163 continue; /* Different username. */ 164 165 /* Found the user and host. */ 166 fclose(f); 167 168 /* If the entry was negated, deny access. */ 169 if (negated) { 170 auth_debug_add("Matched negative entry in %.100s.", 171 filename); 172 return 0; 173 } 174 /* Accept authentication. */ 175 return 1; 176 } 177 178 /* Authentication using this file denied. */ 179 fclose(f); 180 return 0; 181 } 182 183 /* 184 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 185 * true if authentication succeeds. If ignore_rhosts is true, only 186 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 187 */ 188 189 int 190 auth_rhosts(struct passwd *pw, const char *client_user) 191 { 192 const char *hostname, *ipaddr; 193 194 hostname = get_canonical_hostname(options.use_dns); 195 ipaddr = get_remote_ipaddr(); 196 return auth_rhosts2(pw, client_user, hostname, ipaddr); 197 } 198 199 static int 200 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname, 201 const char *ipaddr) 202 { 203 char buf[1024]; 204 struct stat st; 205 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 206 u_int rhosts_file_index; 207 208 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 209 client_user, hostname, ipaddr); 210 211 /* Switch to the user's uid. */ 212 temporarily_use_uid(pw); 213 /* 214 * Quick check: if the user has no .shosts or .rhosts files and 215 * no system hosts.equiv/shosts.equiv files exist then return 216 * failure immediately without doing costly lookups from name 217 * servers. 218 */ 219 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 220 rhosts_file_index++) { 221 /* Check users .rhosts or .shosts. */ 222 snprintf(buf, sizeof buf, "%.500s/%.100s", 223 pw->pw_dir, rhosts_files[rhosts_file_index]); 224 if (stat(buf, &st) >= 0) 225 break; 226 } 227 /* Switch back to privileged uid. */ 228 restore_uid(); 229 230 /* 231 * Deny if The user has no .shosts or .rhosts file and there 232 * are no system-wide files. 233 */ 234 if (!rhosts_files[rhosts_file_index] && 235 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 236 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) { 237 debug3("%s: no hosts access files exist", __func__); 238 return 0; 239 } 240 241 /* 242 * If not logging in as superuser, try /etc/hosts.equiv and 243 * shosts.equiv. 244 */ 245 if (pw->pw_uid == 0) 246 debug3("%s: root user, ignoring system hosts files", __func__); 247 else { 248 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 249 client_user, pw->pw_name)) { 250 auth_debug_add("Accepted for %.100s [%.100s] by " 251 "/etc/hosts.equiv.", hostname, ipaddr); 252 return 1; 253 } 254 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 255 client_user, pw->pw_name)) { 256 auth_debug_add("Accepted for %.100s [%.100s] by " 257 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 258 return 1; 259 } 260 } 261 262 /* 263 * Check that the home directory is owned by root or the user, and is 264 * not group or world writable. 265 */ 266 if (stat(pw->pw_dir, &st) < 0) { 267 logit("Rhosts authentication refused for %.100s: " 268 "no home directory %.200s", pw->pw_name, pw->pw_dir); 269 auth_debug_add("Rhosts authentication refused for %.100s: " 270 "no home directory %.200s", pw->pw_name, pw->pw_dir); 271 return 0; 272 } 273 if (options.strict_modes && 274 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 275 (st.st_mode & 022) != 0)) { 276 logit("Rhosts authentication refused for %.100s: " 277 "bad ownership or modes for home directory.", pw->pw_name); 278 auth_debug_add("Rhosts authentication refused for %.100s: " 279 "bad ownership or modes for home directory.", pw->pw_name); 280 return 0; 281 } 282 /* Temporarily use the user's uid. */ 283 temporarily_use_uid(pw); 284 285 /* Check all .rhosts files (currently .shosts and .rhosts). */ 286 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 287 rhosts_file_index++) { 288 /* Check users .rhosts or .shosts. */ 289 snprintf(buf, sizeof buf, "%.500s/%.100s", 290 pw->pw_dir, rhosts_files[rhosts_file_index]); 291 if (stat(buf, &st) < 0) 292 continue; 293 294 /* 295 * Make sure that the file is either owned by the user or by 296 * root, and make sure it is not writable by anyone but the 297 * owner. This is to help avoid novices accidentally 298 * allowing access to their account by anyone. 299 */ 300 if (options.strict_modes && 301 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 302 (st.st_mode & 022) != 0)) { 303 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 304 pw->pw_name, buf); 305 auth_debug_add("Bad file modes for %.200s", buf); 306 continue; 307 } 308 /* 309 * Check if we have been configured to ignore .rhosts 310 * and .shosts files. 311 */ 312 if (options.ignore_rhosts) { 313 auth_debug_add("Server has been configured to " 314 "ignore %.100s.", rhosts_files[rhosts_file_index]); 315 continue; 316 } 317 /* Check if authentication is permitted by the file. */ 318 if (check_rhosts_file(buf, hostname, ipaddr, 319 client_user, pw->pw_name)) { 320 auth_debug_add("Accepted by %.100s.", 321 rhosts_files[rhosts_file_index]); 322 /* Restore the privileged uid. */ 323 restore_uid(); 324 auth_debug_add("Accepted host %s ip %s client_user " 325 "%s server_user %s", hostname, ipaddr, 326 client_user, pw->pw_name); 327 return 1; 328 } 329 } 330 331 /* Restore the privileged uid. */ 332 restore_uid(); 333 return 0; 334 } 335 336 int 337 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 338 const char *ipaddr) 339 { 340 return auth_rhosts2_raw(pw, client_user, hostname, ipaddr); 341 } 342
