1 /* $NetBSD: auth-rhosts.c,v 1.11 2019/10/12 18:32:22 christos Exp $ */ 2 /* $OpenBSD: auth-rhosts.c,v 1.51 2019/10/02 00:42:30 djm Exp $ */ 3 /* 4 * Author: Tatu Ylonen <ylo@cs.hut.fi> 5 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 6 * All rights reserved 7 * Rhosts authentication. This file contains code to check whether to admit 8 * the login based on rhosts authentication. This file also processes 9 * /etc/hosts.equiv. 10 * 11 * As far as I am concerned, the code I have written for this software 12 * can be used freely for any purpose. Any derived versions of this 13 * software must be clearly marked as such, and if the derived work is 14 * incompatible with the protocol description in the RFC file, it must be 15 * called by a name other than "ssh" or "Secure Shell". 16 */ 17 18 #include "includes.h" 19 __RCSID("$NetBSD: auth-rhosts.c,v 1.11 2019/10/12 18:32:22 christos Exp $"); 20 #include <sys/types.h> 21 #include <sys/stat.h> 22 23 #include <fcntl.h> 24 #include <netgroup.h> 25 #include <pwd.h> 26 #include <stdio.h> 27 #include <string.h> 28 #include <stdarg.h> 29 #include <unistd.h> 30 31 #include "packet.h" 32 #include "uidswap.h" 33 #include "pathnames.h" 34 #include "log.h" 35 #include "misc.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 buf[1024]; 192 struct stat st; 193 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; 194 u_int rhosts_file_index; 195 196 debug2("auth_rhosts2: 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 snprintf(buf, sizeof buf, "%.500s/%.100s", 211 pw->pw_dir, rhosts_files[rhosts_file_index]); 212 if (stat(buf, &st) >= 0) 213 break; 214 } 215 /* Switch back to privileged uid. */ 216 restore_uid(); 217 218 /* 219 * Deny if The user has no .shosts or .rhosts file and there 220 * are no system-wide files. 221 */ 222 if (!rhosts_files[rhosts_file_index] && 223 stat(_PATH_RHOSTS_EQUIV, &st) == -1 && 224 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { 225 debug3("%s: no hosts access files exist", __func__); 226 return 0; 227 } 228 229 /* 230 * If not logging in as superuser, try /etc/hosts.equiv and 231 * shosts.equiv. 232 */ 233 if (pw->pw_uid == 0) 234 debug3("%s: root user, ignoring system hosts files", __func__); 235 else { 236 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, 237 client_user, pw->pw_name)) { 238 auth_debug_add("Accepted for %.100s [%.100s] by " 239 "/etc/hosts.equiv.", hostname, ipaddr); 240 return 1; 241 } 242 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, 243 client_user, pw->pw_name)) { 244 auth_debug_add("Accepted for %.100s [%.100s] by " 245 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); 246 return 1; 247 } 248 } 249 250 /* 251 * Check that the home directory is owned by root or the user, and is 252 * not group or world writable. 253 */ 254 if (stat(pw->pw_dir, &st) == -1) { 255 logit("Rhosts authentication refused for %.100s: " 256 "no home directory %.200s", pw->pw_name, pw->pw_dir); 257 auth_debug_add("Rhosts authentication refused for %.100s: " 258 "no home directory %.200s", pw->pw_name, pw->pw_dir); 259 return 0; 260 } 261 if (options.strict_modes && 262 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 263 (st.st_mode & 022) != 0)) { 264 logit("Rhosts authentication refused for %.100s: " 265 "bad ownership or modes for home directory.", pw->pw_name); 266 auth_debug_add("Rhosts authentication refused for %.100s: " 267 "bad ownership or modes for home directory.", pw->pw_name); 268 return 0; 269 } 270 /* Temporarily use the user's uid. */ 271 temporarily_use_uid(pw); 272 273 /* Check all .rhosts files (currently .shosts and .rhosts). */ 274 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; 275 rhosts_file_index++) { 276 /* Check users .rhosts or .shosts. */ 277 snprintf(buf, sizeof buf, "%.500s/%.100s", 278 pw->pw_dir, rhosts_files[rhosts_file_index]); 279 if (stat(buf, &st) == -1) 280 continue; 281 282 /* 283 * Make sure that the file is either owned by the user or by 284 * root, and make sure it is not writable by anyone but the 285 * owner. This is to help avoid novices accidentally 286 * allowing access to their account by anyone. 287 */ 288 if (options.strict_modes && 289 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 290 (st.st_mode & 022) != 0)) { 291 logit("Rhosts authentication refused for %.100s: bad modes for %.200s", 292 pw->pw_name, buf); 293 auth_debug_add("Bad file modes for %.200s", buf); 294 continue; 295 } 296 /* 297 * Check if we have been configured to ignore .rhosts 298 * and .shosts files. 299 */ 300 if ((pw->pw_uid == 0 && options.ignore_root_rhosts) || 301 (pw->pw_uid != 0 && options.ignore_rhosts)) { 302 auth_debug_add("Server has been configured to " 303 "ignore %.100s.", rhosts_files[rhosts_file_index]); 304 continue; 305 } 306 /* Check if authentication is permitted by the file. */ 307 if (check_rhosts_file(buf, hostname, ipaddr, 308 client_user, pw->pw_name)) { 309 auth_debug_add("Accepted by %.100s.", 310 rhosts_files[rhosts_file_index]); 311 /* Restore the privileged uid. */ 312 restore_uid(); 313 auth_debug_add("Accepted host %s ip %s client_user " 314 "%s server_user %s", hostname, ipaddr, 315 client_user, pw->pw_name); 316 return 1; 317 } 318 } 319 320 /* Restore the privileged uid. */ 321 restore_uid(); 322 return 0; 323 } 324