Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 1 | /* |
| 2 | |
| 3 | auth-rhosts.c |
| 4 | |
| 5 | Author: Tatu Ylonen <ylo@cs.hut.fi> |
| 6 | |
| 7 | Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 8 | All rights reserved |
| 9 | |
| 10 | Created: Fri Mar 17 05:12:18 1995 ylo |
| 11 | |
| 12 | Rhosts authentication. This file contains code to check whether to admit |
| 13 | the login based on rhosts authentication. This file also processes |
| 14 | /etc/hosts.equiv. |
| 15 | |
| 16 | */ |
| 17 | |
| 18 | #include "includes.h" |
| 19 | RCSID("$Id: auth-rhosts.c,v 1.1 1999/10/27 03:42:43 damien Exp $"); |
| 20 | |
| 21 | #include "packet.h" |
| 22 | #include "ssh.h" |
| 23 | #include "xmalloc.h" |
| 24 | #include "uidswap.h" |
| 25 | |
| 26 | /* This function processes an rhosts-style file (.rhosts, .shosts, or |
| 27 | /etc/hosts.equiv). This returns true if authentication can be granted |
| 28 | based on the file, and returns zero otherwise. */ |
| 29 | |
| 30 | int check_rhosts_file(const char *filename, const char *hostname, |
| 31 | const char *ipaddr, const char *client_user, |
| 32 | const char *server_user) |
| 33 | { |
| 34 | FILE *f; |
| 35 | char buf[1024]; /* Must not be larger than host, user, dummy below. */ |
| 36 | |
| 37 | /* Open the .rhosts file. */ |
| 38 | f = fopen(filename, "r"); |
| 39 | if (!f) |
| 40 | return 0; /* Cannot read the .rhosts - deny access. */ |
| 41 | |
| 42 | /* Go through the file, checking every entry. */ |
| 43 | while (fgets(buf, sizeof(buf), f)) |
| 44 | { |
| 45 | /* All three must be at least as big as buf to avoid overflows. */ |
| 46 | char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp; |
| 47 | int negated; |
| 48 | |
| 49 | for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) |
| 50 | ; |
| 51 | if (*cp == '#' || *cp == '\n' || !*cp) |
| 52 | continue; |
| 53 | |
| 54 | /* NO_PLUS is supported at least on OSF/1. We skip it (we don't ever |
| 55 | support the plus syntax). */ |
| 56 | if (strncmp(cp, "NO_PLUS", 7) == 0) |
| 57 | continue; |
| 58 | |
| 59 | /* This should be safe because each buffer is as big as the whole |
| 60 | string, and thus cannot be overwritten. */ |
| 61 | switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) |
| 62 | { |
| 63 | case 0: |
| 64 | packet_send_debug("Found empty line in %.100s.", filename); |
| 65 | continue; /* Empty line? */ |
| 66 | case 1: |
| 67 | /* Host name only. */ |
| 68 | strlcpy(userbuf, server_user, sizeof(userbuf)); |
| 69 | break; |
| 70 | case 2: |
| 71 | /* Got both host and user name. */ |
| 72 | break; |
| 73 | case 3: |
| 74 | packet_send_debug("Found garbage in %.100s.", filename); |
| 75 | continue; /* Extra garbage */ |
| 76 | default: |
| 77 | continue; /* Weird... */ |
| 78 | } |
| 79 | |
| 80 | host = hostbuf; |
| 81 | user = userbuf; |
| 82 | negated = 0; |
| 83 | |
| 84 | /* Process negated host names, or positive netgroups. */ |
| 85 | if (host[0] == '-') |
| 86 | { |
| 87 | negated = 1; |
| 88 | host++; |
| 89 | } |
| 90 | else |
| 91 | if (host[0] == '+') |
| 92 | host++; |
| 93 | |
| 94 | if (user[0] == '-') |
| 95 | { |
| 96 | negated = 1; |
| 97 | user++; |
| 98 | } |
| 99 | else |
| 100 | if (user[0] == '+') |
| 101 | user++; |
| 102 | |
| 103 | /* Check for empty host/user names (particularly '+'). */ |
| 104 | if (!host[0] || !user[0]) |
| 105 | { |
| 106 | /* We come here if either was '+' or '-'. */ |
| 107 | packet_send_debug("Ignoring wild host/user names in %.100s.", |
| 108 | filename); |
| 109 | continue; |
| 110 | } |
| 111 | |
| 112 | /* Verify that host name matches. */ |
| 113 | if (host[0] == '@') |
| 114 | { |
| 115 | if (!innetgr(host + 1, hostname, NULL, NULL) && |
| 116 | !innetgr(host + 1, ipaddr, NULL, NULL)) |
| 117 | continue; |
| 118 | } |
| 119 | else |
| 120 | if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0) |
| 121 | continue; /* Different hostname. */ |
| 122 | |
| 123 | /* Verify that user name matches. */ |
| 124 | if (user[0] == '@') |
| 125 | { |
| 126 | if (!innetgr(user + 1, NULL, client_user, NULL)) |
| 127 | continue; |
| 128 | } |
| 129 | else |
| 130 | if (strcmp(user, client_user) != 0) |
| 131 | continue; /* Different username. */ |
| 132 | |
| 133 | /* Found the user and host. */ |
| 134 | fclose(f); |
| 135 | |
| 136 | /* If the entry was negated, deny access. */ |
| 137 | if (negated) |
| 138 | { |
| 139 | packet_send_debug("Matched negative entry in %.100s.", |
| 140 | filename); |
| 141 | return 0; |
| 142 | } |
| 143 | |
| 144 | /* Accept authentication. */ |
| 145 | return 1; |
| 146 | } |
| 147 | |
| 148 | /* Authentication using this file denied. */ |
| 149 | fclose(f); |
| 150 | return 0; |
| 151 | } |
| 152 | |
| 153 | /* Tries to authenticate the user using the .shosts or .rhosts file. |
| 154 | Returns true if authentication succeeds. If ignore_rhosts is |
| 155 | true, only /etc/hosts.equiv will be considered (.rhosts and .shosts |
| 156 | are ignored). */ |
| 157 | |
| 158 | int auth_rhosts(struct passwd *pw, const char *client_user, |
| 159 | int ignore_rhosts, int strict_modes) |
| 160 | { |
| 161 | char buf[1024]; |
| 162 | const char *hostname, *ipaddr; |
| 163 | int port; |
| 164 | struct stat st; |
| 165 | static const char *rhosts_files[] = { ".shosts", ".rhosts", NULL }; |
| 166 | unsigned int rhosts_file_index; |
| 167 | |
| 168 | /* Quick check: if the user has no .shosts or .rhosts files, return failure |
| 169 | immediately without doing costly lookups from name servers. */ |
| 170 | /* Switch to the user's uid. */ |
| 171 | temporarily_use_uid(pw->pw_uid); |
| 172 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; |
| 173 | rhosts_file_index++) |
| 174 | { |
| 175 | /* Check users .rhosts or .shosts. */ |
| 176 | snprintf(buf, sizeof buf, "%.500s/%.100s", |
| 177 | pw->pw_dir, rhosts_files[rhosts_file_index]); |
| 178 | if (stat(buf, &st) >= 0) |
| 179 | break; |
| 180 | } |
| 181 | /* Switch back to privileged uid. */ |
| 182 | restore_uid(); |
| 183 | |
| 184 | if (!rhosts_files[rhosts_file_index] && stat("/etc/hosts.equiv", &st) < 0 && |
| 185 | stat(SSH_HOSTS_EQUIV, &st) < 0) |
| 186 | return 0; /* The user has no .shosts or .rhosts file and there are no |
| 187 | system-wide files. */ |
| 188 | |
| 189 | /* Get the name, address, and port of the remote host. */ |
| 190 | hostname = get_canonical_hostname(); |
| 191 | ipaddr = get_remote_ipaddr(); |
| 192 | port = get_remote_port(); |
| 193 | |
| 194 | /* Check that the connection comes from a privileged port. |
| 195 | Rhosts authentication only makes sense for priviledged programs. |
| 196 | Of course, if the intruder has root access on his local machine, |
| 197 | he can connect from any port. So do not use .rhosts |
| 198 | authentication from machines that you do not trust. */ |
| 199 | if (port >= IPPORT_RESERVED || |
| 200 | port < IPPORT_RESERVED / 2) |
| 201 | { |
| 202 | log("Connection from %.100s from nonpriviledged port %d", |
| 203 | hostname, port); |
| 204 | packet_send_debug("Your ssh client is not running as root."); |
| 205 | return 0; |
| 206 | } |
| 207 | |
| 208 | /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ |
| 209 | if (pw->pw_uid != 0) |
| 210 | { |
| 211 | if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user, |
| 212 | pw->pw_name)) |
| 213 | { |
| 214 | packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", |
| 215 | hostname, ipaddr); |
| 216 | return 1; |
| 217 | } |
| 218 | if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user, |
| 219 | pw->pw_name)) |
| 220 | { |
| 221 | packet_send_debug("Accepted for %.100s [%.100s] by %.100s.", |
| 222 | hostname, ipaddr, SSH_HOSTS_EQUIV); |
| 223 | return 1; |
| 224 | } |
| 225 | } |
| 226 | |
| 227 | /* Check that the home directory is owned by root or the user, and is not |
| 228 | group or world writable. */ |
| 229 | if (stat(pw->pw_dir, &st) < 0) |
| 230 | { |
| 231 | log("Rhosts authentication refused for %.100: no home directory %.200s", |
| 232 | pw->pw_name, pw->pw_dir); |
| 233 | packet_send_debug("Rhosts authentication refused for %.100: no home directory %.200s", |
| 234 | pw->pw_name, pw->pw_dir); |
| 235 | return 0; |
| 236 | } |
| 237 | if (strict_modes && |
| 238 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || |
| 239 | (st.st_mode & 022) != 0)) |
| 240 | { |
| 241 | log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.", |
| 242 | pw->pw_name); |
| 243 | packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.", |
| 244 | pw->pw_name); |
| 245 | return 0; |
| 246 | } |
| 247 | |
| 248 | /* Check all .rhosts files (currently .shosts and .rhosts). */ |
| 249 | /* Temporarily use the user's uid. */ |
| 250 | temporarily_use_uid(pw->pw_uid); |
| 251 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; |
| 252 | rhosts_file_index++) |
| 253 | { |
| 254 | /* Check users .rhosts or .shosts. */ |
| 255 | snprintf(buf, sizeof buf, "%.500s/%.100s", |
| 256 | pw->pw_dir, rhosts_files[rhosts_file_index]); |
| 257 | if (stat(buf, &st) < 0) |
| 258 | continue; /* No such file. */ |
| 259 | |
| 260 | /* Make sure that the file is either owned by the user or by root, |
| 261 | and make sure it is not writable by anyone but the owner. This is |
| 262 | to help avoid novices accidentally allowing access to their account |
| 263 | by anyone. */ |
| 264 | if (strict_modes && |
| 265 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || |
| 266 | (st.st_mode & 022) != 0)) |
| 267 | { |
| 268 | log("Rhosts authentication refused for %.100s: bad modes for %.200s", |
| 269 | pw->pw_name, buf); |
| 270 | packet_send_debug("Bad file modes for %.200s", buf); |
| 271 | continue; |
| 272 | } |
| 273 | |
| 274 | /* Check if we have been configured to ignore .rhosts and .shosts |
| 275 | files. */ |
| 276 | if (ignore_rhosts) |
| 277 | { |
| 278 | packet_send_debug("Server has been configured to ignore %.100s.", |
| 279 | rhosts_files[rhosts_file_index]); |
| 280 | continue; |
| 281 | } |
| 282 | |
| 283 | /* Check if authentication is permitted by the file. */ |
| 284 | if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) |
| 285 | { |
| 286 | packet_send_debug("Accepted by %.100s.", |
| 287 | rhosts_files[rhosts_file_index]); |
| 288 | /* Restore the privileged uid. */ |
| 289 | restore_uid(); |
| 290 | return 1; |
| 291 | } |
| 292 | } |
| 293 | |
| 294 | /* Rhosts authentication denied. */ |
| 295 | /* Restore the privileged uid. */ |
| 296 | restore_uid(); |
| 297 | return 0; |
| 298 | } |