1 /* $OpenBSD: auth-rhosts.c,v 1.47 2016/03/07 19:02:43 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 "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 "uidswap.h" 34 #include "pathnames.h" 35 #include "log.h" 36 #include "misc.h" 37 #include "buffer.h" /* XXX */ 38 #include "key.h" /* XXX */ 39 #include "servconf.h" 40 #include "canohost.h" 41 #include "sshkey.h" 42 #include "hostfile.h" 43 #include "auth.h" 44 45 /* import */ 46 extern ServerOptions options; 47 extern int use_privsep; 48 49 /* 50 * This function processes an rhosts-style file (.rhosts, .shosts, or 51 * /etc/hosts.equiv). This returns true if authentication can be granted 52 * based on the file, and returns zero otherwise. 53 */ 54 55 static int 56 check_rhosts_file(const char *filename, const char *hostname, 57 const char *ipaddr, const char *client_user, 58 const char *server_user) 59 { 60 FILE *f; 61 #define RBUFLN 1024 62 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 63 int fd; 64 struct stat st; 65 66 /* Open the .rhosts file, deny if unreadable */ 67 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 68 return 0; 69 if (fstat(fd, &st) == -1) { 70 close(fd); 71 return 0; 72 } 73 if (!S_ISREG(st.st_mode)) { 74 logit("User %s hosts file %s is not a regular file", 75 server_user, filename); 76 close(fd); 77 return 0; 78 } 79 unset_nonblock(fd); 80 if ((f = fdopen(fd, "r")) == NULL) { 81 close(fd); 82 return 0; 83 } 84 while (fgets(buf, sizeof(buf), f)) { 85 /* All three must have length >= buf to avoid overflows. */ 86 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 87 char *host, *user, *cp; 88 int negated; 89 90 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 91 ; 92 if (*cp == '#' || *cp == '\n' || !*cp) 93 continue; 94 95 /* 96 * NO_PLUS is supported at least on OSF/1. We skip it (we 97 * don't ever support the plus syntax). 98 */ 99 if (strncmp(cp, "NO_PLUS", 7) == 0) 100 continue; 101 102 /* 103 * This should be safe because each buffer is as big as the 104 * whole string, and thus cannot be overwritten. 105 */ 106 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 107 dummy)) { 108 case 0: 109 auth_debug_add("Found empty line in %.100s.", filename); 110 continue; 111 case 1: 112 /* Host name only. */ 113 strlcpy(userbuf, server_user, sizeof(userbuf)); 114 break; 115 case 2: 116 /* Got both host and user name. */ 117 break; 118 case 3: 119 auth_debug_add("Found garbage in %.100s.", filename); 120 continue; 121 default: 122 /* Weird... */ 123 continue; 124 } 125 126 host = hostbuf; 127 user = userbuf; 128 negated = 0; 129 130 /* Process negated host names, or positive netgroups. */ 131 if (host[0] == '-') { 132 negated = 1; 133 host++; 134 } else if (host[0] == '+') 135 host++; 136 137 if (user[0] == '-') { 138 negated = 1; 139 user++; 140 } else if (user[0] == '+') 141 user++; 142 143 /* Check for empty host/user names (particularly '+'). */ 144 if (!host[0] || !user[0]) { 145 /* We come here if either was '+' or '-'. */ 146 auth_debug_add("Ignoring wild host/user names " 147 "in %.100s.", filename); 148 continue; 149 } 150 /* Verify that host name matches. */ 151 if (host[0] == '@') { 152 if (!innetgr(host + 1, hostname, NULL, NULL) && 153 !innetgr(host + 1, ipaddr, NULL, NULL)) 154 continue; 155 } else if (strcasecmp(host, hostname) && 156 strcmp(host, ipaddr) != 0) 157 continue; /* Different hostname. */ 158 159 /* Verify that user name matches. */ 160 if (user[0] == '@') { 161 if (!innetgr(user + 1, NULL, client_user, NULL)) 162 continue; 163 } else if (strcmp(user, client_user) != 0) 164 continue; /* Different username. */ 165 166 /* Found the user and host. */ 167 fclose(f); 168 169 /* If the entry was negated, deny access. */ 170 if (negated) { 171 auth_debug_add("Matched negative entry in %.100s.", 172 filename); 173 return 0; 174 } 175 /* Accept authentication. */ 176 return 1; 177 } 178 179 /* Authentication using this file denied. */ 180 fclose(f); 181 return 0; 182 } 183 184 /* 185 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 186 * true if authentication succeeds. If ignore_rhosts is true, only 187 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 188 */ 189 190 int 191 auth_rhosts(struct passwd *pw, const char *client_user) 192 { 193 struct ssh *ssh = active_state; /* XXX */ 194 const char *hostname, *ipaddr; 195 196 hostname = auth_get_canonical_hostname(ssh, options.use_dns); 197 ipaddr = ssh_remote_ipaddr(ssh); 198 return auth_rhosts2(pw, client_user, hostname, ipaddr); 199 } 200 201 static int 202 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname, 203 const char *ipaddr) 204 { 205 char buf[1024]; 206 struct stat st; 207 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 208 u_int rhosts_file_index; 209 210 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 211 client_user, hostname, ipaddr); 212 213 /* Switch to the user's uid. */ 214 temporarily_use_uid(pw); 215 /* 216 * Quick check: if the user has no .shosts or .rhosts files and 217 * no system hosts.equiv/shosts.equiv files exist then return 218 * failure immediately without doing costly lookups from name 219 * servers. 220 */ 221 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 222 rhosts_file_index++) { 223 /* Check users .rhosts or .shosts. */ 224 snprintf(buf, sizeof buf, "%.500s/%.100s", 225 pw->pw_dir, rhosts_files[rhosts_file_index]); 226 if (stat(buf, &st) >= 0) 227 break; 228 } 229 /* Switch back to privileged uid. */ 230 restore_uid(); 231 232 /* 233 * Deny if The user has no .shosts or .rhosts file and there 234 * are no system-wide files. 235 */ 236 if (!rhosts_files[rhosts_file_index] && 237 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 238 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) { 239 debug3("%s: no hosts access files exist", __func__); 240 return 0; 241 } 242 243 /* 244 * If not logging in as superuser, try /etc/hosts.equiv and 245 * shosts.equiv. 246 */ 247 if (pw->pw_uid == 0) 248 debug3("%s: root user, ignoring system hosts files", __func__); 249 else { 250 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 251 client_user, pw->pw_name)) { 252 auth_debug_add("Accepted for %.100s [%.100s] by " 253 "/etc/hosts.equiv.", hostname, ipaddr); 254 return 1; 255 } 256 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 257 client_user, pw->pw_name)) { 258 auth_debug_add("Accepted for %.100s [%.100s] by " 259 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 260 return 1; 261 } 262 } 263 264 /* 265 * Check that the home directory is owned by root or the user, and is 266 * not group or world writable. 267 */ 268 if (stat(pw->pw_dir, &st) < 0) { 269 logit("Rhosts authentication refused for %.100s: " 270 "no home directory %.200s", pw->pw_name, pw->pw_dir); 271 auth_debug_add("Rhosts authentication refused for %.100s: " 272 "no home directory %.200s", pw->pw_name, pw->pw_dir); 273 return 0; 274 } 275 if (options.strict_modes && 276 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 277 (st.st_mode & 022) != 0)) { 278 logit("Rhosts authentication refused for %.100s: " 279 "bad ownership or modes for home directory.", pw->pw_name); 280 auth_debug_add("Rhosts authentication refused for %.100s: " 281 "bad ownership or modes for home directory.", pw->pw_name); 282 return 0; 283 } 284 /* Temporarily use the user's uid. */ 285 temporarily_use_uid(pw); 286 287 /* Check all .rhosts files (currently .shosts and .rhosts). */ 288 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 289 rhosts_file_index++) { 290 /* Check users .rhosts or .shosts. */ 291 snprintf(buf, sizeof buf, "%.500s/%.100s", 292 pw->pw_dir, rhosts_files[rhosts_file_index]); 293 if (stat(buf, &st) < 0) 294 continue; 295 296 /* 297 * Make sure that the file is either owned by the user or by 298 * root, and make sure it is not writable by anyone but the 299 * owner. This is to help avoid novices accidentally 300 * allowing access to their account by anyone. 301 */ 302 if (options.strict_modes && 303 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 304 (st.st_mode & 022) != 0)) { 305 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 306 pw->pw_name, buf); 307 auth_debug_add("Bad file modes for %.200s", buf); 308 continue; 309 } 310 /* 311 * Check if we have been configured to ignore .rhosts 312 * and .shosts files. 313 */ 314 if (options.ignore_rhosts) { 315 auth_debug_add("Server has been configured to " 316 "ignore %.100s.", rhosts_files[rhosts_file_index]); 317 continue; 318 } 319 /* Check if authentication is permitted by the file. */ 320 if (check_rhosts_file(buf, hostname, ipaddr, 321 client_user, pw->pw_name)) { 322 auth_debug_add("Accepted by %.100s.", 323 rhosts_files[rhosts_file_index]); 324 /* Restore the privileged uid. */ 325 restore_uid(); 326 auth_debug_add("Accepted host %s ip %s client_user " 327 "%s server_user %s", hostname, ipaddr, 328 client_user, pw->pw_name); 329 return 1; 330 } 331 } 332 333 /* Restore the privileged uid. */ 334 restore_uid(); 335 return 0; 336 } 337 338 int 339 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 340 const char *ipaddr) 341 { 342 return auth_rhosts2_raw(pw, client_user, hostname, ipaddr); 343 } 344