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 1.24 2001/06/23 15:12:17 itojun Exp $"); 18 19 #include "packet.h" 20 #include "xmalloc.h" 21 #include "uidswap.h" 22 #include "pathnames.h" 23 #include "log.h" 24 #include "servconf.h" 25 #include "canohost.h" 26 #include "auth.h" 27 28 /* import */ 29 extern ServerOptions options; 30 31 /* 32 * This function processes an rhosts-style file (.rhosts, .shosts, or 33 * /etc/hosts.equiv). This returns true if authentication can be granted 34 * based on the file, and returns zero otherwise. 35 */ 36 37 static int 38 check_rhosts_file(const char *filename, const char *hostname, 39 const char *ipaddr, const char *client_user, 40 const char *server_user) 41 { 42 FILE *f; 43 char buf[1024]; /* Must not be larger than host, user, dummy below. */ 44 45 /* Open the .rhosts file, deny if unreadable */ 46 f = fopen(filename, "r"); 47 if (!f) 48 return 0; 49 50 while (fgets(buf, sizeof(buf), f)) { 51 /* All three must be at least as big as buf to avoid overflows. */ 52 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp; 53 int negated; 54 55 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 56 ; 57 if (*cp == '#' || *cp == '\n' || !*cp) 58 continue; 59 60 /* 61 * NO_PLUS is supported at least on OSF/1. We skip it (we 62 * don't ever support the plus syntax). 63 */ 64 if (strncmp(cp, "NO_PLUS", 7) == 0) 65 continue; 66 67 /* 68 * This should be safe because each buffer is as big as the 69 * whole string, and thus cannot be overwritten. 70 */ 71 switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) { 72 case 0: 73 packet_send_debug("Found empty line in %.100s.", filename); 74 continue; 75 case 1: 76 /* Host name only. */ 77 strlcpy(userbuf, server_user, sizeof(userbuf)); 78 break; 79 case 2: 80 /* Got both host and user name. */ 81 break; 82 case 3: 83 packet_send_debug("Found garbage in %.100s.", filename); 84 continue; 85 default: 86 /* Weird... */ 87 continue; 88 } 89 90 host = hostbuf; 91 user = userbuf; 92 negated = 0; 93 94 /* Process negated host names, or positive netgroups. */ 95 if (host[0] == '-') { 96 negated = 1; 97 host++; 98 } else if (host[0] == '+') 99 host++; 100 101 if (user[0] == '-') { 102 negated = 1; 103 user++; 104 } else if (user[0] == '+') 105 user++; 106 107 /* Check for empty host/user names (particularly '+'). */ 108 if (!host[0] || !user[0]) { 109 /* We come here if either was '+' or '-'. */ 110 packet_send_debug("Ignoring wild host/user names in %.100s.", 111 filename); 112 continue; 113 } 114 /* Verify that host name matches. */ 115 if (host[0] == '@') { 116 if (!innetgr(host + 1, hostname, NULL, NULL) && 117 !innetgr(host + 1, ipaddr, NULL, NULL)) 118 continue; 119 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0) 120 continue; /* Different hostname. */ 121 122 /* Verify that user name matches. */ 123 if (user[0] == '@') { 124 if (!innetgr(user + 1, NULL, client_user, NULL)) 125 continue; 126 } else if (strcmp(user, client_user) != 0) 127 continue; /* Different username. */ 128 129 /* Found the user and host. */ 130 fclose(f); 131 132 /* If the entry was negated, deny access. */ 133 if (negated) { 134 packet_send_debug("Matched negative entry in %.100s.", 135 filename); 136 return 0; 137 } 138 /* Accept authentication. */ 139 return 1; 140 } 141 142 /* Authentication using this file denied. */ 143 fclose(f); 144 return 0; 145 } 146 147 /* 148 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 149 * true if authentication succeeds. If ignore_rhosts is true, only 150 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 151 */ 152 153 int 154 auth_rhosts(struct passwd *pw, const char *client_user) 155 { 156 const char *hostname, *ipaddr; 157 int ret; 158 159 hostname = get_canonical_hostname(options.reverse_mapping_check); 160 ipaddr = get_remote_ipaddr(); 161 ret = auth_rhosts2(pw, client_user, hostname, ipaddr); 162 return ret; 163 } 164 165 int 166 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 167 const char *ipaddr) 168 { 169 char buf[1024]; 170 struct stat st; 171 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 172 u_int rhosts_file_index; 173 174 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 175 client_user, hostname, ipaddr); 176 177 /* no user given */ 178 if (pw == NULL) 179 return 0; 180 181 /* Switch to the user's uid. */ 182 temporarily_use_uid(pw); 183 /* 184 * Quick check: if the user has no .shosts or .rhosts files, return 185 * failure immediately without doing costly lookups from name 186 * servers. 187 */ 188 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 189 rhosts_file_index++) { 190 /* Check users .rhosts or .shosts. */ 191 snprintf(buf, sizeof buf, "%.500s/%.100s", 192 pw->pw_dir, rhosts_files[rhosts_file_index]); 193 if (stat(buf, &st) >= 0) 194 break; 195 } 196 /* Switch back to privileged uid. */ 197 restore_uid(); 198 199 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */ 200 if (!rhosts_files[rhosts_file_index] && 201 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 202 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) 203 return 0; 204 205 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ 206 if (pw->pw_uid != 0) { 207 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, client_user, 208 pw->pw_name)) { 209 packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", 210 hostname, ipaddr); 211 return 1; 212 } 213 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user, 214 pw->pw_name)) { 215 packet_send_debug("Accepted for %.100s [%.100s] by %.100s.", 216 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 217 return 1; 218 } 219 } 220 /* 221 * Check that the home directory is owned by root or the user, and is 222 * not group or world writable. 223 */ 224 if (stat(pw->pw_dir, &st) < 0) { 225 log("Rhosts authentication refused for %.100s: no home directory %.200s", 226 pw->pw_name, pw->pw_dir); 227 packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s", 228 pw->pw_name, pw->pw_dir); 229 return 0; 230 } 231 if (options.strict_modes && 232 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 233 (st.st_mode & 022) != 0)) { 234 log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.", 235 pw->pw_name); 236 packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.", 237 pw->pw_name); 238 return 0; 239 } 240 /* Temporarily use the user's uid. */ 241 temporarily_use_uid(pw); 242 243 /* Check all .rhosts files (currently .shosts and .rhosts). */ 244 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 245 rhosts_file_index++) { 246 /* Check users .rhosts or .shosts. */ 247 snprintf(buf, sizeof buf, "%.500s/%.100s", 248 pw->pw_dir, rhosts_files[rhosts_file_index]); 249 if (stat(buf, &st) < 0) 250 continue; 251 252 /* 253 * Make sure that the file is either owned by the user or by 254 * root, and make sure it is not writable by anyone but the 255 * owner. This is to help avoid novices accidentally 256 * allowing access to their account by anyone. 257 */ 258 if (options.strict_modes && 259 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 260 (st.st_mode & 022) != 0)) { 261 log("Rhosts authentication refused for %.100s: bad modes for %.200s", 262 pw->pw_name, buf); 263 packet_send_debug("Bad file modes for %.200s", buf); 264 continue; 265 } 266 /* Check if we have been configured to ignore .rhosts and .shosts files. */ 267 if (options.ignore_rhosts) { 268 packet_send_debug("Server has been configured to ignore %.100s.", 269 rhosts_files[rhosts_file_index]); 270 continue; 271 } 272 /* Check if authentication is permitted by the file. */ 273 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) { 274 packet_send_debug("Accepted by %.100s.", 275 rhosts_files[rhosts_file_index]); 276 /* Restore the privileged uid. */ 277 restore_uid(); 278 return 1; 279 } 280 } 281 282 /* Restore the privileged uid. */ 283 restore_uid(); 284 return 0; 285 } 286