1 /* $NetBSD: auth-rhosts.c,v 1.3 2010/11/21 18:29:48 adam Exp $ */ 2 /* $OpenBSD: auth-rhosts.c,v 1.44 2010/03/07 11:57:13 dtucker Exp $ */ 3 /* 4 * Author: Tatu Ylonen <ylo@cs.hut.fi> 5 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 6 * All rights reserved 7 * Rhosts authentication. This file contains code to check whether to admit 8 * the login based on rhosts authentication. This file also processes 9 * /etc/hosts.equiv. 10 * 11 * As far as I am concerned, the code I have written for this software 12 * can be used freely for any purpose. Any derived versions of this 13 * software must be clearly marked as such, and if the derived work is 14 * incompatible with the protocol description in the RFC file, it must be 15 * called by a name other than "ssh" or "Secure Shell". 16 */ 17 18 #include "includes.h" 19 __RCSID("$NetBSD: auth-rhosts.c,v 1.3 2010/11/21 18:29:48 adam Exp $"); 20 #include <sys/types.h> 21 #include <sys/stat.h> 22 23 #include <fcntl.h> 24 #include <netgroup.h> 25 #include <pwd.h> 26 #include <stdio.h> 27 #include <string.h> 28 #include <stdarg.h> 29 #include <unistd.h> 30 31 #include "packet.h" 32 #include "buffer.h" 33 #include "uidswap.h" 34 #include "pathnames.h" 35 #include "log.h" 36 #include "servconf.h" 37 #include "canohost.h" 38 #include "key.h" 39 #include "hostfile.h" 40 #include "auth.h" 41 #include "misc.h" 42 43 /* import */ 44 extern ServerOptions options; 45 extern int use_privsep; 46 47 /* 48 * This function processes an rhosts-style file (.rhosts, .shosts, or 49 * /etc/hosts.equiv). This returns true if authentication can be granted 50 * based on the file, and returns zero otherwise. 51 */ 52 53 static int 54 check_rhosts_file(const char *filename, const char *hostname, 55 const char *ipaddr, const char *client_user, 56 const char *server_user) 57 { 58 FILE *f; 59 char buf[1024]; /* Must not be larger than host, user, dummy below. */ 60 int fd; 61 struct stat st; 62 63 /* Open the .rhosts file, deny if unreadable */ 64 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 65 return 0; 66 if (fstat(fd, &st) == -1) { 67 close(fd); 68 return 0; 69 } 70 if (!S_ISREG(st.st_mode)) { 71 logit("User %s hosts file %s is not a regular file", 72 server_user, filename); 73 close(fd); 74 return 0; 75 } 76 unset_nonblock(fd); 77 if ((f = fdopen(fd, "r")) == NULL) { 78 close(fd); 79 return 0; 80 } 81 while (fgets(buf, sizeof(buf), f)) { 82 /* All three must be at least as big as buf to avoid overflows. */ 83 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp; 84 int negated; 85 86 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 87 ; 88 if (*cp == '#' || *cp == '\n' || !*cp) 89 continue; 90 91 /* 92 * NO_PLUS is supported at least on OSF/1. We skip it (we 93 * don't ever support the plus syntax). 94 */ 95 if (strncmp(cp, "NO_PLUS", 7) == 0) 96 continue; 97 98 /* 99 * This should be safe because each buffer is as big as the 100 * whole string, and thus cannot be overwritten. 101 */ 102 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 103 dummy)) { 104 case 0: 105 auth_debug_add("Found empty line in %.100s.", filename); 106 continue; 107 case 1: 108 /* Host name only. */ 109 strlcpy(userbuf, server_user, sizeof(userbuf)); 110 break; 111 case 2: 112 /* Got both host and user name. */ 113 break; 114 case 3: 115 auth_debug_add("Found garbage in %.100s.", filename); 116 continue; 117 default: 118 /* Weird... */ 119 continue; 120 } 121 122 host = hostbuf; 123 user = userbuf; 124 negated = 0; 125 126 /* Process negated host names, or positive netgroups. */ 127 if (host[0] == '-') { 128 negated = 1; 129 host++; 130 } else if (host[0] == '+') 131 host++; 132 133 if (user[0] == '-') { 134 negated = 1; 135 user++; 136 } else if (user[0] == '+') 137 user++; 138 139 /* Check for empty host/user names (particularly '+'). */ 140 if (!host[0] || !user[0]) { 141 /* We come here if either was '+' or '-'. */ 142 auth_debug_add("Ignoring wild host/user names in %.100s.", 143 filename); 144 continue; 145 } 146 /* Verify that host name matches. */ 147 if (host[0] == '@') { 148 if (!innetgr(host + 1, hostname, NULL, NULL) && 149 !innetgr(host + 1, ipaddr, NULL, NULL)) 150 continue; 151 } else if (strcasecmp(host, hostname) && 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, return 211 * failure immediately without doing costly lookups from name 212 * servers. 213 */ 214 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 215 rhosts_file_index++) { 216 /* Check users .rhosts or .shosts. */ 217 snprintf(buf, sizeof buf, "%.500s/%.100s", 218 pw->pw_dir, rhosts_files[rhosts_file_index]); 219 if (stat(buf, &st) >= 0) 220 break; 221 } 222 /* Switch back to privileged uid. */ 223 restore_uid(); 224 225 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */ 226 if (!rhosts_files[rhosts_file_index] && 227 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 228 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) 229 return 0; 230 231 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ 232 if (pw->pw_uid != 0) { 233 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 234 client_user, pw->pw_name)) { 235 auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", 236 hostname, ipaddr); 237 return 1; 238 } 239 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 240 client_user, pw->pw_name)) { 241 auth_debug_add("Accepted for %.100s [%.100s] by %.100s.", 242 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 243 return 1; 244 } 245 } 246 /* 247 * Check that the home directory is owned by root or the user, and is 248 * not group or world writable. 249 */ 250 if (stat(pw->pw_dir, &st) < 0) { 251 logit("Rhosts authentication refused for %.100s: " 252 "no home directory %.200s", pw->pw_name, pw->pw_dir); 253 auth_debug_add("Rhosts authentication refused for %.100s: " 254 "no home directory %.200s", pw->pw_name, pw->pw_dir); 255 return 0; 256 } 257 if (options.strict_modes && 258 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 259 (st.st_mode & 022) != 0)) { 260 logit("Rhosts authentication refused for %.100s: " 261 "bad ownership or modes for home directory.", pw->pw_name); 262 auth_debug_add("Rhosts authentication refused for %.100s: " 263 "bad ownership or modes for home directory.", pw->pw_name); 264 return 0; 265 } 266 /* Temporarily use the user's uid. */ 267 temporarily_use_uid(pw); 268 269 /* Check all .rhosts files (currently .shosts and .rhosts). */ 270 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 271 rhosts_file_index++) { 272 /* Check users .rhosts or .shosts. */ 273 snprintf(buf, sizeof buf, "%.500s/%.100s", 274 pw->pw_dir, rhosts_files[rhosts_file_index]); 275 if (stat(buf, &st) < 0) 276 continue; 277 278 /* 279 * Make sure that the file is either owned by the user or by 280 * root, and make sure it is not writable by anyone but the 281 * owner. This is to help avoid novices accidentally 282 * allowing access to their account by anyone. 283 */ 284 if (options.strict_modes && 285 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 286 (st.st_mode & 022) != 0)) { 287 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 288 pw->pw_name, buf); 289 auth_debug_add("Bad file modes for %.200s", buf); 290 continue; 291 } 292 /* Check if we have been configured to ignore .rhosts and .shosts files. */ 293 if ((pw->pw_uid == 0 && options.ignore_root_rhosts) || 294 (pw->pw_uid != 0 && 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