1 /* $OpenBSD: auth-rhosts.c,v 1.53 2020/10/18 11:32:01 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 <fcntl.h> 21 #include <netgroup.h> 22 #include <pwd.h> 23 #include <stdio.h> 24 #include <string.h> 25 #include <stdarg.h> 26 #include <unistd.h> 27 28 #include "packet.h" 29 #include "uidswap.h" 30 #include "pathnames.h" 31 #include "log.h" 32 #include "misc.h" 33 #include "sshbuf.h" 34 #include "sshkey.h" 35 #include "servconf.h" 36 #include "canohost.h" 37 #include "hostfile.h" 38 #include "auth.h" 39 40 /* import */ 41 extern ServerOptions options; 42 extern int use_privsep; 43 44 /* 45 * This function processes an rhosts-style file (.rhosts, .shosts, or 46 * /etc/hosts.equiv). This returns true if authentication can be granted 47 * based on the file, and returns zero otherwise. 48 */ 49 50 static int 51 check_rhosts_file(const char *filename, const char *hostname, 52 const char *ipaddr, const char *client_user, 53 const char *server_user) 54 { 55 FILE *f; 56 #define RBUFLN 1024 57 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ 58 int fd; 59 struct stat st; 60 61 /* Open the .rhosts file, deny if unreadable */ 62 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) 63 return 0; 64 if (fstat(fd, &st) == -1) { 65 close(fd); 66 return 0; 67 } 68 if (!S_ISREG(st.st_mode)) { 69 logit("User %s hosts file %s is not a regular file", 70 server_user, filename); 71 close(fd); 72 return 0; 73 } 74 unset_nonblock(fd); 75 if ((f = fdopen(fd, "r")) == NULL) { 76 close(fd); 77 return 0; 78 } 79 while (fgets(buf, sizeof(buf), f)) { 80 /* All three must have length >= buf to avoid overflows. */ 81 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; 82 char *host, *user, *cp; 83 int negated; 84 85 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) 86 ; 87 if (*cp == '#' || *cp == '\n' || !*cp) 88 continue; 89 90 /* 91 * NO_PLUS is supported at least on OSF/1. We skip it (we 92 * don't ever support the plus syntax). 93 */ 94 if (strncmp(cp, "NO_PLUS", 7) == 0) 95 continue; 96 97 /* 98 * This should be safe because each buffer is as big as the 99 * whole string, and thus cannot be overwritten. 100 */ 101 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, 102 dummy)) { 103 case 0: 104 auth_debug_add("Found empty line in %.100s.", filename); 105 continue; 106 case 1: 107 /* Host name only. */ 108 strlcpy(userbuf, server_user, sizeof(userbuf)); 109 break; 110 case 2: 111 /* Got both host and user name. */ 112 break; 113 case 3: 114 auth_debug_add("Found garbage in %.100s.", filename); 115 continue; 116 default: 117 /* Weird... */ 118 continue; 119 } 120 121 host = hostbuf; 122 user = userbuf; 123 negated = 0; 124 125 /* Process negated host names, or positive netgroups. */ 126 if (host[0] == '-') { 127 negated = 1; 128 host++; 129 } else if (host[0] == '+') 130 host++; 131 132 if (user[0] == '-') { 133 negated = 1; 134 user++; 135 } else if (user[0] == '+') 136 user++; 137 138 /* Check for empty host/user names (particularly '+'). */ 139 if (!host[0] || !user[0]) { 140 /* We come here if either was '+' or '-'. */ 141 auth_debug_add("Ignoring wild host/user names " 142 "in %.100s.", filename); 143 continue; 144 } 145 /* Verify that host name matches. */ 146 if (host[0] == '@') { 147 if (!innetgr(host + 1, hostname, NULL, NULL) && 148 !innetgr(host + 1, ipaddr, NULL, NULL)) 149 continue; 150 } else if (strcasecmp(host, hostname) && 151 strcmp(host, ipaddr) != 0) 152 continue; /* Different hostname. */ 153 154 /* Verify that user name matches. */ 155 if (user[0] == '@') { 156 if (!innetgr(user + 1, NULL, client_user, NULL)) 157 continue; 158 } else if (strcmp(user, client_user) != 0) 159 continue; /* Different username. */ 160 161 /* Found the user and host. */ 162 fclose(f); 163 164 /* If the entry was negated, deny access. */ 165 if (negated) { 166 auth_debug_add("Matched negative entry in %.100s.", 167 filename); 168 return 0; 169 } 170 /* Accept authentication. */ 171 return 1; 172 } 173 174 /* Authentication using this file denied. */ 175 fclose(f); 176 return 0; 177 } 178 179 /* 180 * Tries to authenticate the user using the .shosts or .rhosts file. Returns 181 * true if authentication succeeds. If ignore_rhosts is true, only 182 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). 183 */ 184 int 185 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, 186 const char *ipaddr) 187 { 188 char buf[1024]; 189 struct stat st; 190 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 191 u_int rhosts_file_index; 192 193 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", 194 client_user, hostname, ipaddr); 195 196 /* Switch to the user's uid. */ 197 temporarily_use_uid(pw); 198 /* 199 * Quick check: if the user has no .shosts or .rhosts files and 200 * no system hosts.equiv/shosts.equiv files exist then return 201 * failure immediately without doing costly lookups from name 202 * servers. 203 */ 204 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 205 rhosts_file_index++) { 206 /* Check users .rhosts or .shosts. */ 207 snprintf(buf, sizeof buf, "%.500s/%.100s", 208 pw->pw_dir, rhosts_files[rhosts_file_index]); 209 if (stat(buf, &st) >= 0) 210 break; 211 } 212 /* Switch back to privileged uid. */ 213 restore_uid(); 214 215 /* 216 * Deny if The user has no .shosts or .rhosts file and there 217 * are no system-wide files. 218 */ 219 if (!rhosts_files[rhosts_file_index] && 220 stat(_PATH_RHOSTS_EQUIV, &st) == -1 && 221 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { 222 debug3_f("no hosts access files exist"); 223 return 0; 224 } 225 226 /* 227 * If not logging in as superuser, try /etc/hosts.equiv and 228 * shosts.equiv. 229 */ 230 if (pw->pw_uid == 0) 231 debug3_f("root user, ignoring system hosts files"); 232 else { 233 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 234 client_user, pw->pw_name)) { 235 auth_debug_add("Accepted for %.100s [%.100s] by " 236 "/etc/hosts.equiv.", hostname, ipaddr); 237 return 1; 238 } 239 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 240 client_user, pw->pw_name)) { 241 auth_debug_add("Accepted for %.100s [%.100s] by " 242 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 243 return 1; 244 } 245 } 246 247 /* 248 * Check that the home directory is owned by root or the user, and is 249 * not group or world writable. 250 */ 251 if (stat(pw->pw_dir, &st) == -1) { 252 logit("Rhosts authentication refused for %.100s: " 253 "no home directory %.200s", pw->pw_name, pw->pw_dir); 254 auth_debug_add("Rhosts authentication refused for %.100s: " 255 "no home directory %.200s", pw->pw_name, pw->pw_dir); 256 return 0; 257 } 258 if (options.strict_modes && 259 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 260 (st.st_mode & 022) != 0)) { 261 logit("Rhosts authentication refused for %.100s: " 262 "bad ownership or modes for home directory.", pw->pw_name); 263 auth_debug_add("Rhosts authentication refused for %.100s: " 264 "bad ownership or modes for home directory.", pw->pw_name); 265 return 0; 266 } 267 /* Temporarily use the user's uid. */ 268 temporarily_use_uid(pw); 269 270 /* Check all .rhosts files (currently .shosts and .rhosts). */ 271 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 272 rhosts_file_index++) { 273 /* Check users .rhosts or .shosts. */ 274 snprintf(buf, sizeof buf, "%.500s/%.100s", 275 pw->pw_dir, rhosts_files[rhosts_file_index]); 276 if (stat(buf, &st) == -1) 277 continue; 278 279 /* 280 * Make sure that the file is either owned by the user or by 281 * root, and make sure it is not writable by anyone but the 282 * owner. This is to help avoid novices accidentally 283 * allowing access to their account by anyone. 284 */ 285 if (options.strict_modes && 286 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 287 (st.st_mode & 022) != 0)) { 288 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 289 pw->pw_name, buf); 290 auth_debug_add("Bad file modes for %.200s", buf); 291 continue; 292 } 293 /* 294 * Check if we have been configured to ignore .rhosts 295 * and .shosts files. 296 */ 297 if (options.ignore_rhosts == IGNORE_RHOSTS_YES || 298 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS && 299 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) { 300 auth_debug_add("Server has been configured to " 301 "ignore %.100s.", rhosts_files[rhosts_file_index]); 302 continue; 303 } 304 /* Check if authentication is permitted by the file. */ 305 if (check_rhosts_file(buf, hostname, ipaddr, 306 client_user, pw->pw_name)) { 307 auth_debug_add("Accepted by %.100s.", 308 rhosts_files[rhosts_file_index]); 309 /* Restore the privileged uid. */ 310 restore_uid(); 311 auth_debug_add("Accepted host %s ip %s client_user " 312 "%s server_user %s", hostname, ipaddr, 313 client_user, pw->pw_name); 314 return 1; 315 } 316 } 317 318 /* Restore the privileged uid. */ 319 restore_uid(); 320 return 0; 321 } 322