1 /* 2 * Author: Tatu Ylonen <ylo@cs.hut.fi> 3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 4 * All rights reserved 5 * Rhosts authentication. This file contains code to check whether to admit 6 * the login based on rhosts authentication. This file also processes 7 * /etc/hosts.equiv. 8 * 9 * As far as I am concerned, the code I have written for this software 10 * can be used freely for any purpose. Any derived versions of this 11 * software must be clearly marked as such, and if the derived work is 12 * incompatible with the protocol description in the RFC file, it must be 13 * called by a name other than "ssh" or "Secure Shell". 14 */ 15 16 #include "includes.h" 17 RCSID("$OpenBSD: auth-rhosts.c,v 1.28 2002/05/13 21:26:49 markus Exp $"); 18 19 #pragma ident "%Z%%M% %I% %E% SMI" 20 21 #include "packet.h" 22 #include "uidswap.h" 23 #include "pathnames.h" 24 #include "log.h" 25 #include "servconf.h" 26 #include "canohost.h" 27 #include "auth.h" 28 29 /* import */ 30 extern ServerOptions options; 31 extern int use_privsep; 32 33 /* 34 * This function processes an rhosts-style file (.rhosts, .shosts, or 35 * /etc/hosts.equiv). This returns true if authentication can be granted 36 * based on the file, and returns zero otherwise. 37 */ 38 39 static int 40 check_rhosts_file(const char *filename, const char *hostname, 41 const char *ipaddr, const char *client_user, 42 const char *server_user) 43 { 44 FILE *f; 45 char buf[1024]; /* Must not be larger than host, user, dummy below. */ 46 47 /* Open the .rhosts file, deny if unreadable */ 48 f = fopen(filename, "r"); 49 if (!f) 50 return 0; 51 52 while (fgets(buf, sizeof(buf), f)) { 53 /* All three must be at least as big as buf to avoid overflows. */ 54 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp; 55 int negated; 56 57 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 58 ; 59 if (*cp == '#' || *cp == '\n' || !*cp) 60 continue; 61 62 /* 63 * NO_PLUS is supported at least on OSF/1. We skip it (we 64 * don't ever support the plus syntax). 65 */ 66 if (strncmp(cp, "NO_PLUS", 7) == 0) 67 continue; 68 69 /* 70 * This should be safe because each buffer is as big as the 71 * whole string, and thus cannot be overwritten. 72 */ 73 switch (sscanf(buf, "%1024s %1024s %1024s", 74 hostbuf, userbuf, dummy)) { 75 case 0: 76 auth_debug_add("Found empty line in %.100s.", filename); 77 continue; 78 case 1: 79 /* Host name only. */ 80 strlcpy(userbuf, server_user, sizeof(userbuf)); 81 break; 82 case 2: 83 /* Got both host and user name. */ 84 break; 85 case 3: 86 auth_debug_add("Found garbage in %.100s.", filename); 87 continue; 88 default: 89 /* Weird... */ 90 continue; 91 } 92 93 host = hostbuf; 94 user = userbuf; 95 negated = 0; 96 97 /* Process negated host names, or positive netgroups. */ 98 if (host[0] == '-') { 99 negated = 1; 100 host++; 101 } else if (host[0] == '+') 102 host++; 103 104 if (user[0] == '-') { 105 negated = 1; 106 user++; 107 } else if (user[0] == '+') 108 user++; 109 110 /* Check for empty host/user names (particularly '+'). */ 111 if (!host[0] || !user[0]) { 112 /* We come here if either was '+' or '-'. */ 113 auth_debug_add("Ignoring wild host/user names in %.100s.", 114 filename); 115 continue; 116 } 117 /* Verify that host name matches. */ 118 if (host[0] == '@') { 119 if (!innetgr(host + 1, hostname, NULL, NULL) && 120 !innetgr(host + 1, ipaddr, NULL, NULL)) 121 continue; 122 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0) 123 continue; /* Different hostname. */ 124 125 /* Verify that user name matches. */ 126 if (user[0] == '@') { 127 if (!innetgr(user + 1, NULL, client_user, NULL)) 128 continue; 129 } else if (strcmp(user, client_user) != 0) 130 continue; /* Different username. */ 131 132 /* Found the user and host. */ 133 fclose(f); 134 135 /* If the entry was negated, deny access. */ 136 if (negated) { 137 auth_debug_add("Matched negative entry in %.100s.", 138 filename); 139 return 0; 140 } 141 /* Accept authentication. */ 142 return 1; 143 } 144 145 /* Authentication using this file denied. */ 146 fclose(f); 147 return 0; 148 } 149 150 /* 151 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 152 * true if authentication succeeds. If ignore_rhosts is true, only 153 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 154 */ 155 156 int 157 auth_rhosts(struct passwd *pw, const char *client_user) 158 { 159 const char *hostname, *ipaddr; 160 161 hostname = get_canonical_hostname(options.verify_reverse_mapping); 162 ipaddr = get_remote_ipaddr(); 163 return auth_rhosts2(pw, client_user, hostname, ipaddr); 164 } 165 166 static int 167 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname, 168 const char *ipaddr) 169 { 170 char buf[1024]; 171 struct stat st; 172 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 173 u_int rhosts_file_index; 174 175 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 176 client_user, hostname, ipaddr); 177 178 /* no user given */ 179 if (pw == NULL) 180 return 0; 181 182 /* Switch to the user's uid. */ 183 temporarily_use_uid(pw); 184 /* 185 * Quick check: if the user has no .shosts or .rhosts files, return 186 * failure immediately without doing costly lookups from name 187 * servers. 188 */ 189 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 190 rhosts_file_index++) { 191 /* Check users .rhosts or .shosts. */ 192 snprintf(buf, sizeof buf, "%.500s/%.100s", 193 pw->pw_dir, rhosts_files[rhosts_file_index]); 194 if (stat(buf, &st) >= 0) 195 break; 196 } 197 /* Switch back to privileged uid. */ 198 restore_uid(); 199 200 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */ 201 if (!rhosts_files[rhosts_file_index] && 202 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 203 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) 204 return 0; 205 206 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ 207 if (pw->pw_uid != 0) { 208 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 209 client_user, pw->pw_name)) { 210 auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", 211 hostname, ipaddr); 212 return 1; 213 } 214 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 215 client_user, pw->pw_name)) { 216 auth_debug_add("Accepted for %.100s [%.100s] by %.100s.", 217 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 218 return 1; 219 } 220 } 221 /* 222 * Check that the home directory is owned by root or the user, and is 223 * not group or world writable. 224 */ 225 if (stat(pw->pw_dir, &st) < 0) { 226 log("Rhosts authentication refused for %.100s: " 227 "no home directory %.200s", pw->pw_name, pw->pw_dir); 228 auth_debug_add("Rhosts authentication refused for %.100s: " 229 "no home directory %.200s", pw->pw_name, pw->pw_dir); 230 return 0; 231 } 232 if (options.strict_modes && 233 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 234 (st.st_mode & 022) != 0)) { 235 log("Rhosts authentication refused for %.100s: " 236 "bad ownership or modes for home directory.", pw->pw_name); 237 auth_debug_add("Rhosts authentication refused for %.100s: " 238 "bad ownership or modes for home directory.", pw->pw_name); 239 return 0; 240 } 241 /* Temporarily use the user's uid. */ 242 temporarily_use_uid(pw); 243 244 /* Check all .rhosts files (currently .shosts and .rhosts). */ 245 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 246 rhosts_file_index++) { 247 /* Check users .rhosts or .shosts. */ 248 snprintf(buf, sizeof buf, "%.500s/%.100s", 249 pw->pw_dir, rhosts_files[rhosts_file_index]); 250 if (stat(buf, &st) < 0) 251 continue; 252 253 /* 254 * Make sure that the file is either owned by the user or by 255 * root, and make sure it is not writable by anyone but the 256 * owner. This is to help avoid novices accidentally 257 * allowing access to their account by anyone. 258 */ 259 if (options.strict_modes && 260 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 261 (st.st_mode & 022) != 0)) { 262 log("Rhosts authentication refused for %.100s: bad modes for %.200s", 263 pw->pw_name, buf); 264 auth_debug_add("Bad file modes for %.200s", buf); 265 continue; 266 } 267 /* Check if we have been configured to ignore .rhosts and .shosts files. */ 268 if (options.ignore_rhosts) { 269 auth_debug_add("Server has been configured to ignore %.100s.", 270 rhosts_files[rhosts_file_index]); 271 continue; 272 } 273 /* Check if authentication is permitted by the file. */ 274 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) { 275 auth_debug_add("Accepted by %.100s.", 276 rhosts_files[rhosts_file_index]); 277 /* Restore the privileged uid. */ 278 restore_uid(); 279 auth_debug_add("Accepted host %s ip %s client_user %s server_user %s", 280 hostname, ipaddr, client_user, pw->pw_name); 281 return 1; 282 } 283 } 284 285 /* Restore the privileged uid. */ 286 restore_uid(); 287 return 0; 288 } 289 290 int 291 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 292 const char *ipaddr) 293 { 294 int ret; 295 296 auth_debug_reset(); 297 ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr); 298 if (!use_privsep) 299 auth_debug_send(); 300 return ret; 301 } 302