1 /* $OpenBSD: auth-rhosts.c,v 1.55 2022/02/23 11:15:57 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 #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 "xmalloc.h" 38 #include "sshbuf.h" 39 #include "sshkey.h" 40 #include "servconf.h" 41 #include "canohost.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 *path = NULL; 194 struct stat st; 195 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL}; 196 u_int rhosts_file_index; 197 int r; 198 199 debug2_f("clientuser %s hostname %s ipaddr %s", 200 client_user, hostname, ipaddr); 201 202 /* Switch to the user's uid. */ 203 temporarily_use_uid(pw); 204 /* 205 * Quick check: if the user has no .shosts or .rhosts files and 206 * no system hosts.equiv/shosts.equiv files exist then return 207 * failure immediately without doing costly lookups from name 208 * servers. 209 */ 210 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 211 rhosts_file_index++) { 212 /* Check users .rhosts or .shosts. */ 213 xasprintf(&path, "%s/%s", 214 pw->pw_dir, rhosts_files[rhosts_file_index]); 215 r = stat(path, &st); 216 free(path); 217 if (r >= 0) 218 break; 219 } 220 /* Switch back to privileged uid. */ 221 restore_uid(); 222 223 /* 224 * Deny if The user has no .shosts or .rhosts file and there 225 * are no system-wide files. 226 */ 227 if (!rhosts_files[rhosts_file_index] && 228 stat(_PATH_RHOSTS_EQUIV, &st) == -1 && 229 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { 230 debug3_f("no hosts access files exist"); 231 return 0; 232 } 233 234 /* 235 * If not logging in as superuser, try /etc/hosts.equiv and 236 * shosts.equiv. 237 */ 238 if (pw->pw_uid == 0) 239 debug3_f("root user, ignoring system hosts files"); 240 else { 241 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 242 client_user, pw->pw_name)) { 243 auth_debug_add("Accepted for %.100s [%.100s] by " 244 "/etc/hosts.equiv.", hostname, ipaddr); 245 return 1; 246 } 247 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 248 client_user, pw->pw_name)) { 249 auth_debug_add("Accepted for %.100s [%.100s] by " 250 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 251 return 1; 252 } 253 } 254 255 /* 256 * Check that the home directory is owned by root or the user, and is 257 * not group or world writable. 258 */ 259 if (stat(pw->pw_dir, &st) == -1) { 260 logit("Rhosts authentication refused for %.100s: " 261 "no home directory %.200s", pw->pw_name, pw->pw_dir); 262 auth_debug_add("Rhosts authentication refused for %.100s: " 263 "no home directory %.200s", pw->pw_name, pw->pw_dir); 264 return 0; 265 } 266 if (options.strict_modes && 267 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 268 (st.st_mode & 022) != 0)) { 269 logit("Rhosts authentication refused for %.100s: " 270 "bad ownership or modes for home directory.", pw->pw_name); 271 auth_debug_add("Rhosts authentication refused for %.100s: " 272 "bad ownership or modes for home directory.", pw->pw_name); 273 return 0; 274 } 275 /* Temporarily use the user's uid. */ 276 temporarily_use_uid(pw); 277 278 /* Check all .rhosts files (currently .shosts and .rhosts). */ 279 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 280 rhosts_file_index++) { 281 /* Check users .rhosts or .shosts. */ 282 xasprintf(&path, "%s/%s", 283 pw->pw_dir, rhosts_files[rhosts_file_index]); 284 if (stat(path, &st) == -1) { 285 free(path); 286 continue; 287 } 288 289 /* 290 * Make sure that the file is either owned by the user or by 291 * root, and make sure it is not writable by anyone but the 292 * owner. This is to help avoid novices accidentally 293 * allowing access to their account by anyone. 294 */ 295 if (options.strict_modes && 296 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 297 (st.st_mode & 022) != 0)) { 298 logit("Rhosts authentication refused for %.100s: " 299 "bad modes for %.200s", pw->pw_name, path); 300 auth_debug_add("Bad file modes for %.200s", path); 301 free(path); 302 continue; 303 } 304 /* 305 * Check if we have been configured to ignore .rhosts 306 * and .shosts files. 307 */ 308 if (options.ignore_rhosts == IGNORE_RHOSTS_YES || 309 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS && 310 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) { 311 auth_debug_add("Server has been configured to " 312 "ignore %.100s.", rhosts_files[rhosts_file_index]); 313 free(path); 314 continue; 315 } 316 /* Check if authentication is permitted by the file. */ 317 if (check_rhosts_file(path, hostname, ipaddr, 318 client_user, pw->pw_name)) { 319 auth_debug_add("Accepted by %.100s.", 320 rhosts_files[rhosts_file_index]); 321 /* Restore the privileged uid. */ 322 restore_uid(); 323 auth_debug_add("Accepted host %s ip %s client_user " 324 "%s server_user %s", hostname, ipaddr, 325 client_user, pw->pw_name); 326 free(path); 327 return 1; 328 } 329 free(path); 330 } 331 332 /* Restore the privileged uid. */ 333 restore_uid(); 334 return 0; 335 } 336