1 /* $OpenBSD: auth-rhosts.c,v 1.58 2024/05/17 00:30:23 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 <sys/types.h> 18 #include <sys/stat.h> 19 20 #include <errno.h> 21 #include <fcntl.h> 22 #include <netgroup.h> 23 #include <pwd.h> 24 #include <stdio.h> 25 #include <string.h> 26 #include <stdarg.h> 27 #include <stdlib.h> 28 #include <unistd.h> 29 30 #include "packet.h" 31 #include "uidswap.h" 32 #include "pathnames.h" 33 #include "log.h" 34 #include "misc.h" 35 #include "xmalloc.h" 36 #include "sshbuf.h" 37 #include "sshkey.h" 38 #include "servconf.h" 39 #include "canohost.h" 40 #include "hostfile.h" 41 #include "auth.h" 42 43 /* import */ 44 extern ServerOptions options; 45 46 /* 47 * This function processes an rhosts-style file (.rhosts, .shosts, or 48 * /etc/hosts.equiv). This returns true if authentication can be granted 49 * based on the file, and returns zero otherwise. 50 */ 51 52 static int 53 check_rhosts_file(const char *filename, const char *hostname, 54 const char *ipaddr, const char *client_user, 55 const char *server_user) 56 { 57 FILE *f; 58 #define RBUFLN 1024 59 char buf[RBUFLN];/* 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 have length >= buf to avoid overflows. */ 83 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 84 char *host, *user, *cp; 85 int negated; 86 87 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 88 ; 89 if (*cp == '#' || *cp == '\n' || !*cp) 90 continue; 91 92 /* 93 * NO_PLUS is supported at least on OSF/1. We skip it (we 94 * don't ever support the plus syntax). 95 */ 96 if (strncmp(cp, "NO_PLUS", 7) == 0) 97 continue; 98 99 /* 100 * This should be safe because each buffer is as big as the 101 * whole string, and thus cannot be overwritten. 102 */ 103 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 104 dummy)) { 105 case 0: 106 auth_debug_add("Found empty line in %.100s.", filename); 107 continue; 108 case 1: 109 /* Host name only. */ 110 strlcpy(userbuf, server_user, sizeof(userbuf)); 111 break; 112 case 2: 113 /* Got both host and user name. */ 114 break; 115 case 3: 116 auth_debug_add("Found garbage in %.100s.", filename); 117 continue; 118 default: 119 /* Weird... */ 120 continue; 121 } 122 123 host = hostbuf; 124 user = userbuf; 125 negated = 0; 126 127 /* Process negated host names, or positive netgroups. */ 128 if (host[0] == '-') { 129 negated = 1; 130 host++; 131 } else if (host[0] == '+') 132 host++; 133 134 if (user[0] == '-') { 135 negated = 1; 136 user++; 137 } else if (user[0] == '+') 138 user++; 139 140 /* Check for empty host/user names (particularly '+'). */ 141 if (!host[0] || !user[0]) { 142 /* We come here if either was '+' or '-'. */ 143 auth_debug_add("Ignoring wild host/user names " 144 "in %.100s.", filename); 145 continue; 146 } 147 /* Verify that host name matches. */ 148 if (host[0] == '@') { 149 if (!innetgr(host + 1, hostname, NULL, NULL) && 150 !innetgr(host + 1, ipaddr, NULL, NULL)) 151 continue; 152 } else if (strcasecmp(host, hostname) && 153 strcmp(host, ipaddr) != 0) 154 continue; /* Different hostname. */ 155 156 /* Verify that user name matches. */ 157 if (user[0] == '@') { 158 if (!innetgr(user + 1, NULL, client_user, NULL)) 159 continue; 160 } else if (strcmp(user, client_user) != 0) 161 continue; /* Different username. */ 162 163 /* Found the user and host. */ 164 fclose(f); 165 166 /* If the entry was negated, deny access. */ 167 if (negated) { 168 auth_debug_add("Matched negative entry in %.100s.", 169 filename); 170 return 0; 171 } 172 /* Accept authentication. */ 173 return 1; 174 } 175 176 /* Authentication using this file denied. */ 177 fclose(f); 178 return 0; 179 } 180 181 /* 182 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 183 * true if authentication succeeds. If ignore_rhosts is true, only 184 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 185 */ 186 int 187 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 188 const char *ipaddr) 189 { 190 char *path = NULL; 191 struct stat st; 192 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL}; 193 u_int rhosts_file_index; 194 int r; 195 196 debug2_f("clientuser %s hostname %s ipaddr %s", 197 client_user, hostname, ipaddr); 198 199 /* Switch to the user's uid. */ 200 temporarily_use_uid(pw); 201 /* 202 * Quick check: if the user has no .shosts or .rhosts files and 203 * no system hosts.equiv/shosts.equiv files exist then return 204 * failure immediately without doing costly lookups from name 205 * servers. 206 */ 207 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 208 rhosts_file_index++) { 209 /* Check users .rhosts or .shosts. */ 210 xasprintf(&path, "%s/%s", 211 pw->pw_dir, rhosts_files[rhosts_file_index]); 212 r = stat(path, &st); 213 free(path); 214 if (r >= 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) == -1 && 226 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { 227 debug3_f("no hosts access files exist"); 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_f("root user, ignoring system hosts files"); 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) == -1) { 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 xasprintf(&path, "%s/%s", 280 pw->pw_dir, rhosts_files[rhosts_file_index]); 281 if (stat(path, &st) == -1) { 282 debug3_f("stat %s: %s", path, strerror(errno)); 283 free(path); 284 continue; 285 } 286 287 /* 288 * Make sure that the file is either owned by the user or by 289 * root, and make sure it is not writable by anyone but the 290 * owner. This is to help avoid novices accidentally 291 * allowing access to their account by anyone. 292 */ 293 if (options.strict_modes && 294 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 295 (st.st_mode & 022) != 0)) { 296 logit("Rhosts authentication refused for %.100s: " 297 "bad modes for %.200s", pw->pw_name, path); 298 auth_debug_add("Bad file modes for %.200s", path); 299 free(path); 300 continue; 301 } 302 /* 303 * Check if we have been configured to ignore .rhosts 304 * and .shosts files. 305 */ 306 if (options.ignore_rhosts == IGNORE_RHOSTS_YES || 307 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS && 308 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) { 309 auth_debug_add("Server has been configured to " 310 "ignore %.100s.", rhosts_files[rhosts_file_index]); 311 free(path); 312 continue; 313 } 314 /* Check if authentication is permitted by the file. */ 315 if (check_rhosts_file(path, hostname, ipaddr, 316 client_user, pw->pw_name)) { 317 auth_debug_add("Accepted by %.100s.", 318 rhosts_files[rhosts_file_index]); 319 /* Restore the privileged uid. */ 320 restore_uid(); 321 auth_debug_add("Accepted host %s ip %s client_user " 322 "%s server_user %s", hostname, ipaddr, 323 client_user, pw->pw_name); 324 free(path); 325 return 1; 326 } 327 free(path); 328 } 329 330 /* Restore the privileged uid. */ 331 restore_uid(); 332 return 0; 333 } 334