1 /* $OpenBSD: auth-rhosts.c,v 1.56 2022/02/23 21:21:49 djm 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 #include <fcntl.h> 23 #ifdef HAVE_NETGROUP_H 24 # include <netgroup.h> 25 #endif 26 #include <pwd.h> 27 #include <stdio.h> 28 #include <string.h> 29 #include <stdarg.h> 30 #include <stdlib.h> 31 #include <unistd.h> 32 33 #include "packet.h" 34 #include "uidswap.h" 35 #include "pathnames.h" 36 #include "log.h" 37 #include "misc.h" 38 #include "xmalloc.h" 39 #include "sshbuf.h" 40 #include "sshkey.h" 41 #include "servconf.h" 42 #include "canohost.h" 43 #include "hostfile.h" 44 #include "auth.h" 45 46 /* import */ 47 extern ServerOptions options; 48 extern int use_privsep; 49 50 /* 51 * This function processes an rhosts-style file (.rhosts, .shosts, or 52 * /etc/hosts.equiv). This returns true if authentication can be granted 53 * based on the file, and returns zero otherwise. 54 */ 55 56 static int 57 check_rhosts_file(const char *filename, const char *hostname, 58 const char *ipaddr, const char *client_user, 59 const char *server_user) 60 { 61 FILE *f; 62 #define RBUFLN 1024 63 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 64 int fd; 65 struct stat st; 66 67 /* Open the .rhosts file, deny if unreadable */ 68 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 69 return 0; 70 if (fstat(fd, &st) == -1) { 71 close(fd); 72 return 0; 73 } 74 if (!S_ISREG(st.st_mode)) { 75 logit("User %s hosts file %s is not a regular file", 76 server_user, filename); 77 close(fd); 78 return 0; 79 } 80 unset_nonblock(fd); 81 if ((f = fdopen(fd, "r")) == NULL) { 82 close(fd); 83 return 0; 84 } 85 while (fgets(buf, sizeof(buf), f)) { 86 /* All three must have length >= buf to avoid overflows. */ 87 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 88 char *host, *user, *cp; 89 int negated; 90 91 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 92 ; 93 if (*cp == '#' || *cp == '\n' || !*cp) 94 continue; 95 96 /* 97 * NO_PLUS is supported at least on OSF/1. We skip it (we 98 * don't ever support the plus syntax). 99 */ 100 if (strncmp(cp, "NO_PLUS", 7) == 0) 101 continue; 102 103 /* 104 * This should be safe because each buffer is as big as the 105 * whole string, and thus cannot be overwritten. 106 */ 107 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 108 dummy)) { 109 case 0: 110 auth_debug_add("Found empty line in %.100s.", filename); 111 continue; 112 case 1: 113 /* Host name only. */ 114 strlcpy(userbuf, server_user, sizeof(userbuf)); 115 break; 116 case 2: 117 /* Got both host and user name. */ 118 break; 119 case 3: 120 auth_debug_add("Found garbage in %.100s.", filename); 121 continue; 122 default: 123 /* Weird... */ 124 continue; 125 } 126 127 host = hostbuf; 128 user = userbuf; 129 negated = 0; 130 131 /* Process negated host names, or positive netgroups. */ 132 if (host[0] == '-') { 133 negated = 1; 134 host++; 135 } else if (host[0] == '+') 136 host++; 137 138 if (user[0] == '-') { 139 negated = 1; 140 user++; 141 } else if (user[0] == '+') 142 user++; 143 144 /* Check for empty host/user names (particularly '+'). */ 145 if (!host[0] || !user[0]) { 146 /* We come here if either was '+' or '-'. */ 147 auth_debug_add("Ignoring wild host/user names " 148 "in %.100s.", filename); 149 continue; 150 } 151 /* Verify that host name matches. */ 152 if (host[0] == '@') { 153 if (!innetgr(host + 1, hostname, NULL, NULL) && 154 !innetgr(host + 1, ipaddr, NULL, NULL)) 155 continue; 156 } else if (strcasecmp(host, hostname) && 157 strcmp(host, ipaddr) != 0) 158 continue; /* Different hostname. */ 159 160 /* Verify that user name matches. */ 161 if (user[0] == '@') { 162 if (!innetgr(user + 1, NULL, client_user, NULL)) 163 continue; 164 } else if (strcmp(user, client_user) != 0) 165 continue; /* Different username. */ 166 167 /* Found the user and host. */ 168 fclose(f); 169 170 /* If the entry was negated, deny access. */ 171 if (negated) { 172 auth_debug_add("Matched negative entry in %.100s.", 173 filename); 174 return 0; 175 } 176 /* Accept authentication. */ 177 return 1; 178 } 179 180 /* Authentication using this file denied. */ 181 fclose(f); 182 return 0; 183 } 184 185 /* 186 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 187 * true if authentication succeeds. If ignore_rhosts is true, only 188 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 189 */ 190 int 191 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 192 const char *ipaddr) 193 { 194 char *path = NULL; 195 struct stat st; 196 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL}; 197 u_int rhosts_file_index; 198 int r; 199 200 debug2_f("clientuser %s hostname %s ipaddr %s", 201 client_user, hostname, ipaddr); 202 203 /* Switch to the user's uid. */ 204 temporarily_use_uid(pw); 205 /* 206 * Quick check: if the user has no .shosts or .rhosts files and 207 * no system hosts.equiv/shosts.equiv files exist then return 208 * failure immediately without doing costly lookups from name 209 * servers. 210 */ 211 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 212 rhosts_file_index++) { 213 /* Check users .rhosts or .shosts. */ 214 xasprintf(&path, "%s/%s", 215 pw->pw_dir, rhosts_files[rhosts_file_index]); 216 r = stat(path, &st); 217 free(path); 218 if (r >= 0) 219 break; 220 } 221 /* Switch back to privileged uid. */ 222 restore_uid(); 223 224 /* 225 * Deny if The user has no .shosts or .rhosts file and there 226 * are no system-wide files. 227 */ 228 if (!rhosts_files[rhosts_file_index] && 229 stat(_PATH_RHOSTS_EQUIV, &st) == -1 && 230 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { 231 debug3_f("no hosts access files exist"); 232 return 0; 233 } 234 235 /* 236 * If not logging in as superuser, try /etc/hosts.equiv and 237 * shosts.equiv. 238 */ 239 if (pw->pw_uid == 0) 240 debug3_f("root user, ignoring system hosts files"); 241 else { 242 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 243 client_user, pw->pw_name)) { 244 auth_debug_add("Accepted for %.100s [%.100s] by " 245 "/etc/hosts.equiv.", hostname, ipaddr); 246 return 1; 247 } 248 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 249 client_user, pw->pw_name)) { 250 auth_debug_add("Accepted for %.100s [%.100s] by " 251 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 252 return 1; 253 } 254 } 255 256 /* 257 * Check that the home directory is owned by root or the user, and is 258 * not group or world writable. 259 */ 260 if (stat(pw->pw_dir, &st) == -1) { 261 logit("Rhosts authentication refused for %.100s: " 262 "no home directory %.200s", pw->pw_name, pw->pw_dir); 263 auth_debug_add("Rhosts authentication refused for %.100s: " 264 "no home directory %.200s", pw->pw_name, pw->pw_dir); 265 return 0; 266 } 267 if (options.strict_modes && 268 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 269 (st.st_mode & 022) != 0)) { 270 logit("Rhosts authentication refused for %.100s: " 271 "bad ownership or modes for home directory.", pw->pw_name); 272 auth_debug_add("Rhosts authentication refused for %.100s: " 273 "bad ownership or modes for home directory.", pw->pw_name); 274 return 0; 275 } 276 /* Temporarily use the user's uid. */ 277 temporarily_use_uid(pw); 278 279 /* Check all .rhosts files (currently .shosts and .rhosts). */ 280 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 281 rhosts_file_index++) { 282 /* Check users .rhosts or .shosts. */ 283 xasprintf(&path, "%s/%s", 284 pw->pw_dir, rhosts_files[rhosts_file_index]); 285 if (stat(path, &st) == -1) { 286 free(path); 287 continue; 288 } 289 290 /* 291 * Make sure that the file is either owned by the user or by 292 * root, and make sure it is not writable by anyone but the 293 * owner. This is to help avoid novices accidentally 294 * allowing access to their account by anyone. 295 */ 296 if (options.strict_modes && 297 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 298 (st.st_mode & 022) != 0)) { 299 logit("Rhosts authentication refused for %.100s: " 300 "bad modes for %.200s", pw->pw_name, path); 301 auth_debug_add("Bad file modes for %.200s", path); 302 free(path); 303 continue; 304 } 305 /* 306 * Check if we have been configured to ignore .rhosts 307 * and .shosts files. 308 */ 309 if (options.ignore_rhosts == IGNORE_RHOSTS_YES || 310 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS && 311 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) { 312 auth_debug_add("Server has been configured to " 313 "ignore %.100s.", rhosts_files[rhosts_file_index]); 314 free(path); 315 continue; 316 } 317 /* Check if authentication is permitted by the file. */ 318 if (check_rhosts_file(path, hostname, ipaddr, 319 client_user, pw->pw_name)) { 320 auth_debug_add("Accepted by %.100s.", 321 rhosts_files[rhosts_file_index]); 322 /* Restore the privileged uid. */ 323 restore_uid(); 324 auth_debug_add("Accepted host %s ip %s client_user " 325 "%s server_user %s", hostname, ipaddr, 326 client_user, pw->pw_name); 327 free(path); 328 return 1; 329 } 330 free(path); 331 } 332 333 /* Restore the privileged uid. */ 334 restore_uid(); 335 return 0; 336 } 337