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 <sys/types.h> 18 #include <sys/stat.h> 19 20 #include <fcntl.h> 21 #include <netgroup.h> 22 #include <pwd.h> 23 #include <stdio.h> 24 #include <string.h> 25 #include <stdarg.h> 26 #include <unistd.h> 27 28 #include "packet.h" 29 #include "uidswap.h" 30 #include "pathnames.h" 31 #include "log.h" 32 #include "misc.h" 33 #include "sshbuf.h" 34 #include "sshkey.h" 35 #include "servconf.h" 36 #include "canohost.h" 37 #include "sshkey.h" 38 #include "hostfile.h" 39 #include "auth.h" 40 41 /* import */ 42 extern ServerOptions options; 43 extern int use_privsep; 44 45 /* 46 * This function processes an rhosts-style file (.rhosts, .shosts, or 47 * /etc/hosts.equiv). This returns true if authentication can be granted 48 * based on the file, and returns zero otherwise. 49 */ 50 51 static int 52 check_rhosts_file(const char *filename, const char *hostname, 53 const char *ipaddr, const char *client_user, 54 const char *server_user) 55 { 56 FILE *f; 57 #define RBUFLN 1024 58 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 59 int fd; 60 struct stat st; 61 62 /* Open the .rhosts file, deny if unreadable */ 63 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 64 return 0; 65 if (fstat(fd, &st) == -1) { 66 close(fd); 67 return 0; 68 } 69 if (!S_ISREG(st.st_mode)) { 70 logit("User %s hosts file %s is not a regular file", 71 server_user, filename); 72 close(fd); 73 return 0; 74 } 75 unset_nonblock(fd); 76 if ((f = fdopen(fd, "r")) == NULL) { 77 close(fd); 78 return 0; 79 } 80 while (fgets(buf, sizeof(buf), f)) { 81 /* All three must have length >= buf to avoid overflows. */ 82 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 83 char *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 " 143 "in %.100s.", 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) && 152 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 int 186 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 187 const char *ipaddr) 188 { 189 char buf[1024]; 190 struct stat st; 191 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 192 u_int rhosts_file_index; 193 194 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 195 client_user, hostname, ipaddr); 196 197 /* Switch to the user's uid. */ 198 temporarily_use_uid(pw); 199 /* 200 * Quick check: if the user has no .shosts or .rhosts files and 201 * no system hosts.equiv/shosts.equiv files exist then return 202 * failure immediately without doing costly lookups from name 203 * servers. 204 */ 205 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 206 rhosts_file_index++) { 207 /* Check users .rhosts or .shosts. */ 208 snprintf(buf, sizeof buf, "%.500s/%.100s", 209 pw->pw_dir, rhosts_files[rhosts_file_index]); 210 if (stat(buf, &st) >= 0) 211 break; 212 } 213 /* Switch back to privileged uid. */ 214 restore_uid(); 215 216 /* 217 * Deny if The user has no .shosts or .rhosts file and there 218 * are no system-wide files. 219 */ 220 if (!rhosts_files[rhosts_file_index] && 221 stat(_PATH_RHOSTS_EQUIV, &st) < 0 && 222 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) { 223 debug3("%s: no hosts access files exist", __func__); 224 return 0; 225 } 226 227 /* 228 * If not logging in as superuser, try /etc/hosts.equiv and 229 * shosts.equiv. 230 */ 231 if (pw->pw_uid == 0) 232 debug3("%s: root user, ignoring system hosts files", __func__); 233 else { 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 " 237 "/etc/hosts.equiv.", 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 " 243 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 244 return 1; 245 } 246 } 247 248 /* 249 * Check that the home directory is owned by root or the user, and is 250 * not group or world writable. 251 */ 252 if (stat(pw->pw_dir, &st) < 0) { 253 logit("Rhosts authentication refused for %.100s: " 254 "no home directory %.200s", pw->pw_name, pw->pw_dir); 255 auth_debug_add("Rhosts authentication refused for %.100s: " 256 "no home directory %.200s", pw->pw_name, pw->pw_dir); 257 return 0; 258 } 259 if (options.strict_modes && 260 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 261 (st.st_mode & 022) != 0)) { 262 logit("Rhosts authentication refused for %.100s: " 263 "bad ownership or modes for home directory.", pw->pw_name); 264 auth_debug_add("Rhosts authentication refused for %.100s: " 265 "bad ownership or modes for home directory.", pw->pw_name); 266 return 0; 267 } 268 /* Temporarily use the user's uid. */ 269 temporarily_use_uid(pw); 270 271 /* Check all .rhosts files (currently .shosts and .rhosts). */ 272 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 273 rhosts_file_index++) { 274 /* Check users .rhosts or .shosts. */ 275 snprintf(buf, sizeof buf, "%.500s/%.100s", 276 pw->pw_dir, rhosts_files[rhosts_file_index]); 277 if (stat(buf, &st) < 0) 278 continue; 279 280 /* 281 * Make sure that the file is either owned by the user or by 282 * root, and make sure it is not writable by anyone but the 283 * owner. This is to help avoid novices accidentally 284 * allowing access to their account by anyone. 285 */ 286 if (options.strict_modes && 287 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 288 (st.st_mode & 022) != 0)) { 289 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 290 pw->pw_name, buf); 291 auth_debug_add("Bad file modes for %.200s", buf); 292 continue; 293 } 294 /* 295 * Check if we have been configured to ignore .rhosts 296 * and .shosts files. 297 */ 298 if (options.ignore_rhosts) { 299 auth_debug_add("Server has been configured to " 300 "ignore %.100s.", rhosts_files[rhosts_file_index]); 301 continue; 302 } 303 /* Check if authentication is permitted by the file. */ 304 if (check_rhosts_file(buf, hostname, ipaddr, 305 client_user, pw->pw_name)) { 306 auth_debug_add("Accepted by %.100s.", 307 rhosts_files[rhosts_file_index]); 308 /* Restore the privileged uid. */ 309 restore_uid(); 310 auth_debug_add("Accepted host %s ip %s client_user " 311 "%s server_user %s", hostname, ipaddr, 312 client_user, pw->pw_name); 313 return 1; 314 } 315 } 316 317 /* Restore the privileged uid. */ 318 restore_uid(); 319 return 0; 320 } 321