1 /* $OpenBSD: auth-rhosts.c,v 1.57 2022/12/09 00:17:40 dtucker 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 <errno.h> 23 #include <fcntl.h> 24 #ifdef HAVE_NETGROUP_H 25 # include <netgroup.h> 26 #endif 27 #include <pwd.h> 28 #include <stdio.h> 29 #include <string.h> 30 #include <stdarg.h> 31 #include <stdlib.h> 32 #include <unistd.h> 33 34 #include "packet.h" 35 #include "uidswap.h" 36 #include "pathnames.h" 37 #include "log.h" 38 #include "misc.h" 39 #include "xmalloc.h" 40 #include "sshbuf.h" 41 #include "sshkey.h" 42 #include "servconf.h" 43 #include "canohost.h" 44 #include "hostfile.h" 45 #include "auth.h" 46 47 /* import */ 48 extern ServerOptions options; 49 extern int use_privsep; 50 51 /* 52 * This function processes an rhosts-style file (.rhosts, .shosts, or 53 * /etc/hosts.equiv). This returns true if authentication can be granted 54 * based on the file, and returns zero otherwise. 55 */ 56 57 static int 58 check_rhosts_file(const char *filename, const char *hostname, 59 const char *ipaddr, const char *client_user, 60 const char *server_user) 61 { 62 FILE *f; 63 #define RBUFLN 1024 64 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 65 int fd; 66 struct stat st; 67 68 /* Open the .rhosts file, deny if unreadable */ 69 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 70 return 0; 71 if (fstat(fd, &st) == -1) { 72 close(fd); 73 return 0; 74 } 75 if (!S_ISREG(st.st_mode)) { 76 logit("User %s hosts file %s is not a regular file", 77 server_user, filename); 78 close(fd); 79 return 0; 80 } 81 unset_nonblock(fd); 82 if ((f = fdopen(fd, "r")) == NULL) { 83 close(fd); 84 return 0; 85 } 86 while (fgets(buf, sizeof(buf), f)) { 87 /* All three must have length >= buf to avoid overflows. */ 88 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 89 char *host, *user, *cp; 90 int negated; 91 92 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 93 ; 94 if (*cp == '#' || *cp == '\n' || !*cp) 95 continue; 96 97 /* 98 * NO_PLUS is supported at least on OSF/1. We skip it (we 99 * don't ever support the plus syntax). 100 */ 101 if (strncmp(cp, "NO_PLUS", 7) == 0) 102 continue; 103 104 /* 105 * This should be safe because each buffer is as big as the 106 * whole string, and thus cannot be overwritten. 107 */ 108 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 109 dummy)) { 110 case 0: 111 auth_debug_add("Found empty line in %.100s.", filename); 112 continue; 113 case 1: 114 /* Host name only. */ 115 strlcpy(userbuf, server_user, sizeof(userbuf)); 116 break; 117 case 2: 118 /* Got both host and user name. */ 119 break; 120 case 3: 121 auth_debug_add("Found garbage in %.100s.", filename); 122 continue; 123 default: 124 /* Weird... */ 125 continue; 126 } 127 128 host = hostbuf; 129 user = userbuf; 130 negated = 0; 131 132 /* Process negated host names, or positive netgroups. */ 133 if (host[0] == '-') { 134 negated = 1; 135 host++; 136 } else if (host[0] == '+') 137 host++; 138 139 if (user[0] == '-') { 140 negated = 1; 141 user++; 142 } else if (user[0] == '+') 143 user++; 144 145 /* Check for empty host/user names (particularly '+'). */ 146 if (!host[0] || !user[0]) { 147 /* We come here if either was '+' or '-'. */ 148 auth_debug_add("Ignoring wild host/user names " 149 "in %.100s.", filename); 150 continue; 151 } 152 /* Verify that host name matches. */ 153 if (host[0] == '@') { 154 if (!innetgr(host + 1, hostname, NULL, NULL) && 155 !innetgr(host + 1, ipaddr, NULL, NULL)) 156 continue; 157 } else if (strcasecmp(host, hostname) && 158 strcmp(host, ipaddr) != 0) 159 continue; /* Different hostname. */ 160 161 /* Verify that user name matches. */ 162 if (user[0] == '@') { 163 if (!innetgr(user + 1, NULL, client_user, NULL)) 164 continue; 165 } else if (strcmp(user, client_user) != 0) 166 continue; /* Different username. */ 167 168 /* Found the user and host. */ 169 fclose(f); 170 171 /* If the entry was negated, deny access. */ 172 if (negated) { 173 auth_debug_add("Matched negative entry in %.100s.", 174 filename); 175 return 0; 176 } 177 /* Accept authentication. */ 178 return 1; 179 } 180 181 /* Authentication using this file denied. */ 182 fclose(f); 183 return 0; 184 } 185 186 /* 187 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 188 * true if authentication succeeds. If ignore_rhosts is true, only 189 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 190 */ 191 int 192 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 193 const char *ipaddr) 194 { 195 char *path = NULL; 196 struct stat st; 197 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL}; 198 u_int rhosts_file_index; 199 int r; 200 201 debug2_f("clientuser %s hostname %s ipaddr %s", 202 client_user, hostname, ipaddr); 203 204 /* Switch to the user's uid. */ 205 temporarily_use_uid(pw); 206 /* 207 * Quick check: if the user has no .shosts or .rhosts files and 208 * no system hosts.equiv/shosts.equiv files exist then return 209 * failure immediately without doing costly lookups from name 210 * servers. 211 */ 212 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 213 rhosts_file_index++) { 214 /* Check users .rhosts or .shosts. */ 215 xasprintf(&path, "%s/%s", 216 pw->pw_dir, rhosts_files[rhosts_file_index]); 217 r = stat(path, &st); 218 free(path); 219 if (r >= 0) 220 break; 221 } 222 /* Switch back to privileged uid. */ 223 restore_uid(); 224 225 /* 226 * Deny if The user has no .shosts or .rhosts file and there 227 * are no system-wide files. 228 */ 229 if (!rhosts_files[rhosts_file_index] && 230 stat(_PATH_RHOSTS_EQUIV, &st) == -1 && 231 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { 232 debug3_f("no hosts access files exist"); 233 return 0; 234 } 235 236 /* 237 * If not logging in as superuser, try /etc/hosts.equiv and 238 * shosts.equiv. 239 */ 240 if (pw->pw_uid == 0) 241 debug3_f("root user, ignoring system hosts files"); 242 else { 243 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 244 client_user, pw->pw_name)) { 245 auth_debug_add("Accepted for %.100s [%.100s] by " 246 "/etc/hosts.equiv.", hostname, ipaddr); 247 return 1; 248 } 249 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 250 client_user, pw->pw_name)) { 251 auth_debug_add("Accepted for %.100s [%.100s] by " 252 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 253 return 1; 254 } 255 } 256 257 /* 258 * Check that the home directory is owned by root or the user, and is 259 * not group or world writable. 260 */ 261 if (stat(pw->pw_dir, &st) == -1) { 262 logit("Rhosts authentication refused for %.100s: " 263 "no home directory %.200s", pw->pw_name, pw->pw_dir); 264 auth_debug_add("Rhosts authentication refused for %.100s: " 265 "no home directory %.200s", pw->pw_name, pw->pw_dir); 266 return 0; 267 } 268 if (options.strict_modes && 269 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 270 (st.st_mode & 022) != 0)) { 271 logit("Rhosts authentication refused for %.100s: " 272 "bad ownership or modes for home directory.", pw->pw_name); 273 auth_debug_add("Rhosts authentication refused for %.100s: " 274 "bad ownership or modes for home directory.", pw->pw_name); 275 return 0; 276 } 277 /* Temporarily use the user's uid. */ 278 temporarily_use_uid(pw); 279 280 /* Check all .rhosts files (currently .shosts and .rhosts). */ 281 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 282 rhosts_file_index++) { 283 /* Check users .rhosts or .shosts. */ 284 xasprintf(&path, "%s/%s", 285 pw->pw_dir, rhosts_files[rhosts_file_index]); 286 if (stat(path, &st) == -1) { 287 debug3_f("stat %s: %s", path, strerror(errno)); 288 free(path); 289 continue; 290 } 291 292 /* 293 * Make sure that the file is either owned by the user or by 294 * root, and make sure it is not writable by anyone but the 295 * owner. This is to help avoid novices accidentally 296 * allowing access to their account by anyone. 297 */ 298 if (options.strict_modes && 299 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 300 (st.st_mode & 022) != 0)) { 301 logit("Rhosts authentication refused for %.100s: " 302 "bad modes for %.200s", pw->pw_name, path); 303 auth_debug_add("Bad file modes for %.200s", path); 304 free(path); 305 continue; 306 } 307 /* 308 * Check if we have been configured to ignore .rhosts 309 * and .shosts files. 310 */ 311 if (options.ignore_rhosts == IGNORE_RHOSTS_YES || 312 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS && 313 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) { 314 auth_debug_add("Server has been configured to " 315 "ignore %.100s.", rhosts_files[rhosts_file_index]); 316 free(path); 317 continue; 318 } 319 /* Check if authentication is permitted by the file. */ 320 if (check_rhosts_file(path, hostname, ipaddr, 321 client_user, pw->pw_name)) { 322 auth_debug_add("Accepted by %.100s.", 323 rhosts_files[rhosts_file_index]); 324 /* Restore the privileged uid. */ 325 restore_uid(); 326 auth_debug_add("Accepted host %s ip %s client_user " 327 "%s server_user %s", hostname, ipaddr, 328 client_user, pw->pw_name); 329 free(path); 330 return 1; 331 } 332 free(path); 333 } 334 335 /* Restore the privileged uid. */ 336 restore_uid(); 337 return 0; 338 } 339