1 /* $OpenBSD: auth-rhosts.c,v 1.46 2014/12/23 22:42:48 djm 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 <sys/types.h> 18 #include <sys/stat.h> 19 20 #include <fcntl.h> 21 #include <netgroup.h> 22 #include <pwd.h> 23 #include <stdio.h> 24 #include <string.h> 25 #include <stdarg.h> 26 #include <unistd.h> 27 28 #include "packet.h" 29 #include "buffer.h" 30 #include "uidswap.h" 31 #include "pathnames.h" 32 #include "log.h" 33 #include "misc.h" 34 #include "servconf.h" 35 #include "canohost.h" 36 #include "key.h" 37 #include "hostfile.h" 38 #include "auth.h" 39 40 /* import */ 41 extern ServerOptions options; 42 extern int use_privsep; 43 44 /* 45 * This function processes an rhosts-style file (.rhosts, .shosts, or 46 * /etc/hosts.equiv). This returns true if authentication can be granted 47 * based on the file, and returns zero otherwise. 48 */ 49 50 static int 51 check_rhosts_file(const char *filename, const char *hostname, 52 const char *ipaddr, const char *client_user, 53 const char *server_user) 54 { 55 FILE *f; 56 #define RBUFLN 1024 57 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 58 int fd; 59 struct stat st; 60 61 /* Open the .rhosts file, deny if unreadable */ 62 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 63 return 0; 64 if (fstat(fd, &st) == -1) { 65 close(fd); 66 return 0; 67 } 68 if (!S_ISREG(st.st_mode)) { 69 logit("User %s hosts file %s is not a regular file", 70 server_user, filename); 71 close(fd); 72 return 0; 73 } 74 unset_nonblock(fd); 75 if ((f = fdopen(fd, "r")) == NULL) { 76 close(fd); 77 return 0; 78 } 79 while (fgets(buf, sizeof(buf), f)) { 80 /* All three must have length >= buf to avoid overflows. */ 81 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 82 char *host, *user, *cp; 83 int negated; 84 85 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 86 ; 87 if (*cp == '#' || *cp == '\n' || !*cp) 88 continue; 89 90 /* 91 * NO_PLUS is supported at least on OSF/1. We skip it (we 92 * don't ever support the plus syntax). 93 */ 94 if (strncmp(cp, "NO_PLUS", 7) == 0) 95 continue; 96 97 /* 98 * This should be safe because each buffer is as big as the 99 * whole string, and thus cannot be overwritten. 100 */ 101 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 102 dummy)) { 103 case 0: 104 auth_debug_add("Found empty line in %.100s.", filename); 105 continue; 106 case 1: 107 /* Host name only. */ 108 strlcpy(userbuf, server_user, sizeof(userbuf)); 109 break; 110 case 2: 111 /* Got both host and user name. */ 112 break; 113 case 3: 114 auth_debug_add("Found garbage in %.100s.", filename); 115 continue; 116 default: 117 /* Weird... */ 118 continue; 119 } 120 121 host = hostbuf; 122 user = userbuf; 123 negated = 0; 124 125 /* Process negated host names, or positive netgroups. */ 126 if (host[0] == '-') { 127 negated = 1; 128 host++; 129 } else if (host[0] == '+') 130 host++; 131 132 if (user[0] == '-') { 133 negated = 1; 134 user++; 135 } else if (user[0] == '+') 136 user++; 137 138 /* Check for empty host/user names (particularly '+'). */ 139 if (!host[0] || !user[0]) { 140 /* We come here if either was '+' or '-'. */ 141 auth_debug_add("Ignoring wild host/user names " 142 "in %.100s.", filename); 143 continue; 144 } 145 /* Verify that host name matches. */ 146 if (host[0] == '@') { 147 if (!innetgr(host + 1, hostname, NULL, NULL) && 148 !innetgr(host + 1, ipaddr, NULL, NULL)) 149 continue; 150 } else if (strcasecmp(host, hostname) && 151 strcmp(host, ipaddr) != 0) 152 continue; /* Different hostname. */ 153 154 /* Verify that user name matches. */ 155 if (user[0] == '@') { 156 if (!innetgr(user + 1, NULL, client_user, NULL)) 157 continue; 158 } else if (strcmp(user, client_user) != 0) 159 continue; /* Different username. */ 160 161 /* Found the user and host. */ 162 fclose(f); 163 164 /* If the entry was negated, deny access. */ 165 if (negated) { 166 auth_debug_add("Matched negative entry in %.100s.", 167 filename); 168 return 0; 169 } 170 /* Accept authentication. */ 171 return 1; 172 } 173 174 /* Authentication using this file denied. */ 175 fclose(f); 176 return 0; 177 } 178 179 /* 180 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 181 * true if authentication succeeds. If ignore_rhosts is true, only 182 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 183 */ 184 185 int 186 auth_rhosts(struct passwd *pw, const char *client_user) 187 { 188 const char *hostname, *ipaddr; 189 190 hostname = get_canonical_hostname(options.use_dns); 191 ipaddr = get_remote_ipaddr(); 192 return auth_rhosts2(pw, client_user, hostname, ipaddr); 193 } 194 195 static int 196 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname, 197 const char *ipaddr) 198 { 199 char buf[1024]; 200 struct stat st; 201 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 202 u_int rhosts_file_index; 203 204 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 205 client_user, hostname, ipaddr); 206 207 /* Switch to the user's uid. */ 208 temporarily_use_uid(pw); 209 /* 210 * Quick check: if the user has no .shosts or .rhosts files and 211 * no system hosts.equiv/shosts.equiv files exist then 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 /* 227 * Deny if The user has no .shosts or .rhosts file and there 228 * are no system-wide files. 229 */ 230 if (!rhosts_files[rhosts_file_index] && 231 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 232 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) { 233 debug3("%s: no hosts access files exist", __func__); 234 return 0; 235 } 236 237 /* 238 * If not logging in as superuser, try /etc/hosts.equiv and 239 * shosts.equiv. 240 */ 241 if (pw->pw_uid == 0) 242 debug3("%s: root user, ignoring system hosts files", __func__); 243 else { 244 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 245 client_user, pw->pw_name)) { 246 auth_debug_add("Accepted for %.100s [%.100s] by " 247 "/etc/hosts.equiv.", hostname, ipaddr); 248 return 1; 249 } 250 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 251 client_user, pw->pw_name)) { 252 auth_debug_add("Accepted for %.100s [%.100s] by " 253 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 254 return 1; 255 } 256 } 257 258 /* 259 * Check that the home directory is owned by root or the user, and is 260 * not group or world writable. 261 */ 262 if (stat(pw->pw_dir, &st) < 0) { 263 logit("Rhosts authentication refused for %.100s: " 264 "no home directory %.200s", pw->pw_name, pw->pw_dir); 265 auth_debug_add("Rhosts authentication refused for %.100s: " 266 "no home directory %.200s", pw->pw_name, pw->pw_dir); 267 return 0; 268 } 269 if (options.strict_modes && 270 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 271 (st.st_mode & 022) != 0)) { 272 logit("Rhosts authentication refused for %.100s: " 273 "bad ownership or modes for home directory.", pw->pw_name); 274 auth_debug_add("Rhosts authentication refused for %.100s: " 275 "bad ownership or modes for home directory.", pw->pw_name); 276 return 0; 277 } 278 /* Temporarily use the user's uid. */ 279 temporarily_use_uid(pw); 280 281 /* Check all .rhosts files (currently .shosts and .rhosts). */ 282 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 283 rhosts_file_index++) { 284 /* Check users .rhosts or .shosts. */ 285 snprintf(buf, sizeof buf, "%.500s/%.100s", 286 pw->pw_dir, rhosts_files[rhosts_file_index]); 287 if (stat(buf, &st) < 0) 288 continue; 289 290 /* 291 * Make sure that the file is either owned by the user or by 292 * root, and make sure it is not writable by anyone but the 293 * owner. This is to help avoid novices accidentally 294 * allowing access to their account by anyone. 295 */ 296 if (options.strict_modes && 297 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 298 (st.st_mode & 022) != 0)) { 299 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 300 pw->pw_name, buf); 301 auth_debug_add("Bad file modes for %.200s", buf); 302 continue; 303 } 304 /* 305 * Check if we have been configured to ignore .rhosts 306 * and .shosts files. 307 */ 308 if (options.ignore_rhosts) { 309 auth_debug_add("Server has been configured to " 310 "ignore %.100s.", rhosts_files[rhosts_file_index]); 311 continue; 312 } 313 /* Check if authentication is permitted by the file. */ 314 if (check_rhosts_file(buf, hostname, ipaddr, 315 client_user, pw->pw_name)) { 316 auth_debug_add("Accepted by %.100s.", 317 rhosts_files[rhosts_file_index]); 318 /* Restore the privileged uid. */ 319 restore_uid(); 320 auth_debug_add("Accepted host %s ip %s client_user " 321 "%s server_user %s", hostname, ipaddr, 322 client_user, pw->pw_name); 323 return 1; 324 } 325 } 326 327 /* Restore the privileged uid. */ 328 restore_uid(); 329 return 0; 330 } 331 332 int 333 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 334 const char *ipaddr) 335 { 336 return auth_rhosts2_raw(pw, client_user, hostname, ipaddr); 337 } 338