1 /* $OpenBSD: auth-rhosts.c,v 1.45 2014/07/15 15:54:14 millert 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 "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 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 } 322