1 /* $OpenBSD: auth-rhosts.c,v 1.49 2018/07/09 21:35:50 markus 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 "sshbuf.h" 38 #include "sshkey.h" 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 int 190 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 191 const char *ipaddr) 192 { 193 char buf[1024]; 194 struct stat st; 195 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 196 u_int rhosts_file_index; 197 198 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 199 client_user, hostname, ipaddr); 200 201 /* Switch to the user's uid. */ 202 temporarily_use_uid(pw); 203 /* 204 * Quick check: if the user has no .shosts or .rhosts files and 205 * no system hosts.equiv/shosts.equiv files exist then return 206 * failure immediately without doing costly lookups from name 207 * servers. 208 */ 209 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 210 rhosts_file_index++) { 211 /* Check users .rhosts or .shosts. */ 212 snprintf(buf, sizeof buf, "%.500s/%.100s", 213 pw->pw_dir, rhosts_files[rhosts_file_index]); 214 if (stat(buf, &st) >= 0) 215 break; 216 } 217 /* Switch back to privileged uid. */ 218 restore_uid(); 219 220 /* 221 * Deny if The user has no .shosts or .rhosts file and there 222 * are no system-wide files. 223 */ 224 if (!rhosts_files[rhosts_file_index] && 225 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 226 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) { 227 debug3("%s: no hosts access files exist", __func__); 228 return 0; 229 } 230 231 /* 232 * If not logging in as superuser, try /etc/hosts.equiv and 233 * shosts.equiv. 234 */ 235 if (pw->pw_uid == 0) 236 debug3("%s: root user, ignoring system hosts files", __func__); 237 else { 238 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 239 client_user, pw->pw_name)) { 240 auth_debug_add("Accepted for %.100s [%.100s] by " 241 "/etc/hosts.equiv.", hostname, ipaddr); 242 return 1; 243 } 244 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 245 client_user, pw->pw_name)) { 246 auth_debug_add("Accepted for %.100s [%.100s] by " 247 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 248 return 1; 249 } 250 } 251 252 /* 253 * Check that the home directory is owned by root or the user, and is 254 * not group or world writable. 255 */ 256 if (stat(pw->pw_dir, &st) < 0) { 257 logit("Rhosts authentication refused for %.100s: " 258 "no home directory %.200s", pw->pw_name, pw->pw_dir); 259 auth_debug_add("Rhosts authentication refused for %.100s: " 260 "no home directory %.200s", pw->pw_name, pw->pw_dir); 261 return 0; 262 } 263 if (options.strict_modes && 264 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 265 (st.st_mode & 022) != 0)) { 266 logit("Rhosts authentication refused for %.100s: " 267 "bad ownership or modes for home directory.", pw->pw_name); 268 auth_debug_add("Rhosts authentication refused for %.100s: " 269 "bad ownership or modes for home directory.", pw->pw_name); 270 return 0; 271 } 272 /* Temporarily use the user's uid. */ 273 temporarily_use_uid(pw); 274 275 /* Check all .rhosts files (currently .shosts and .rhosts). */ 276 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 277 rhosts_file_index++) { 278 /* Check users .rhosts or .shosts. */ 279 snprintf(buf, sizeof buf, "%.500s/%.100s", 280 pw->pw_dir, rhosts_files[rhosts_file_index]); 281 if (stat(buf, &st) < 0) 282 continue; 283 284 /* 285 * Make sure that the file is either owned by the user or by 286 * root, and make sure it is not writable by anyone but the 287 * owner. This is to help avoid novices accidentally 288 * allowing access to their account by anyone. 289 */ 290 if (options.strict_modes && 291 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 292 (st.st_mode & 022) != 0)) { 293 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 294 pw->pw_name, buf); 295 auth_debug_add("Bad file modes for %.200s", buf); 296 continue; 297 } 298 /* 299 * Check if we have been configured to ignore .rhosts 300 * and .shosts files. 301 */ 302 if (options.ignore_rhosts) { 303 auth_debug_add("Server has been configured to " 304 "ignore %.100s.", rhosts_files[rhosts_file_index]); 305 continue; 306 } 307 /* Check if authentication is permitted by the file. */ 308 if (check_rhosts_file(buf, hostname, ipaddr, 309 client_user, pw->pw_name)) { 310 auth_debug_add("Accepted by %.100s.", 311 rhosts_files[rhosts_file_index]); 312 /* Restore the privileged uid. */ 313 restore_uid(); 314 auth_debug_add("Accepted host %s ip %s client_user " 315 "%s server_user %s", hostname, ipaddr, 316 client_user, pw->pw_name); 317 return 1; 318 } 319 } 320 321 /* Restore the privileged uid. */ 322 restore_uid(); 323 return 0; 324 } 325