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