5 Author: Tatu Ylonen <ylo@cs.hut.fi>
7 Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
10 Created: Fri Mar 17 05:12:18 1995 ylo
12 Rhosts authentication. This file contains code to check whether to admit
13 the login based on rhosts authentication. This file also processes
27 /* This function processes an rhosts-style file (.rhosts, .shosts, or
28 /etc/hosts.equiv). This returns true if authentication can be granted
29 based on the file, and returns zero otherwise. */
31 int check_rhosts_file(const char *filename, const char *hostname,
32 const char *ipaddr, const char *client_user,
33 const char *server_user)
36 char buf[1024]; /* Must not be larger than host, user, dummy below. */
38 /* Open the .rhosts file. */
39 f = fopen(filename, "r");
41 return 0; /* Cannot read the .rhosts - deny access. */
43 /* Go through the file, checking every entry. */
44 while (fgets(buf, sizeof(buf), f))
46 /* All three must be at least as big as buf to avoid overflows. */
47 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
50 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
52 if (*cp == '#' || *cp == '\n' || !*cp)
55 /* NO_PLUS is supported at least on OSF/1. We skip it (we don't ever
56 support the plus syntax). */
57 if (strncmp(cp, "NO_PLUS", 7) == 0)
60 /* This should be safe because each buffer is as big as the whole
61 string, and thus cannot be overwritten. */
62 switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy))
65 packet_send_debug("Found empty line in %.100s.", filename);
66 continue; /* Empty line? */
69 strlcpy(userbuf, server_user, sizeof(userbuf));
72 /* Got both host and user name. */
75 packet_send_debug("Found garbage in %.100s.", filename);
76 continue; /* Extra garbage */
78 continue; /* Weird... */
85 /* Process negated host names, or positive netgroups. */
104 /* Check for empty host/user names (particularly '+'). */
105 if (!host[0] || !user[0])
107 /* We come here if either was '+' or '-'. */
108 packet_send_debug("Ignoring wild host/user names in %.100s.",
113 /* Verify that host name matches. */
116 if (!innetgr(host + 1, hostname, NULL, NULL) &&
117 !innetgr(host + 1, ipaddr, NULL, NULL))
121 if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
122 continue; /* Different hostname. */
124 /* Verify that user name matches. */
127 if (!innetgr(user + 1, NULL, client_user, NULL))
131 if (strcmp(user, client_user) != 0)
132 continue; /* Different username. */
134 /* Found the user and host. */
137 /* If the entry was negated, deny access. */
140 packet_send_debug("Matched negative entry in %.100s.",
145 /* Accept authentication. */
149 /* Authentication using this file denied. */
154 /* Tries to authenticate the user using the .shosts or .rhosts file.
155 Returns true if authentication succeeds. If ignore_rhosts is
156 true, only /etc/hosts.equiv will be considered (.rhosts and .shosts
159 int auth_rhosts(struct passwd *pw, const char *client_user)
161 extern ServerOptions options;
163 const char *hostname, *ipaddr;
166 static const char *rhosts_files[] = { ".shosts", ".rhosts", NULL };
167 unsigned int rhosts_file_index;
169 /* Quick check: if the user has no .shosts or .rhosts files, return failure
170 immediately without doing costly lookups from name servers. */
171 /* Switch to the user's uid. */
172 temporarily_use_uid(pw->pw_uid);
173 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
176 /* Check users .rhosts or .shosts. */
177 snprintf(buf, sizeof buf, "%.500s/%.100s",
178 pw->pw_dir, rhosts_files[rhosts_file_index]);
179 if (stat(buf, &st) >= 0)
182 /* Switch back to privileged uid. */
185 if (!rhosts_files[rhosts_file_index] && stat("/etc/hosts.equiv", &st) < 0 &&
186 stat(SSH_HOSTS_EQUIV, &st) < 0)
187 return 0; /* The user has no .shosts or .rhosts file and there are no
188 system-wide files. */
190 /* Get the name, address, and port of the remote host. */
191 hostname = get_canonical_hostname();
192 ipaddr = get_remote_ipaddr();
193 port = get_remote_port();
195 /* Check that the connection comes from a privileged port.
196 Rhosts authentication only makes sense for priviledged programs.
197 Of course, if the intruder has root access on his local machine,
198 he can connect from any port. So do not use .rhosts
199 authentication from machines that you do not trust. */
200 if (port >= IPPORT_RESERVED ||
201 port < IPPORT_RESERVED / 2)
203 log("Connection from %.100s from nonpriviledged port %d",
205 packet_send_debug("Your ssh client is not running as root.");
209 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
212 if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
215 packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
219 if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
222 packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
223 hostname, ipaddr, SSH_HOSTS_EQUIV);
228 /* Check that the home directory is owned by root or the user, and is not
229 group or world writable. */
230 if (stat(pw->pw_dir, &st) < 0)
232 log("Rhosts authentication refused for %.100: no home directory %.200s",
233 pw->pw_name, pw->pw_dir);
234 packet_send_debug("Rhosts authentication refused for %.100: no home directory %.200s",
235 pw->pw_name, pw->pw_dir);
238 if (options.strict_modes &&
239 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
240 (st.st_mode & 022) != 0))
242 log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
244 packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
249 /* Check all .rhosts files (currently .shosts and .rhosts). */
250 /* Temporarily use the user's uid. */
251 temporarily_use_uid(pw->pw_uid);
252 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
255 /* Check users .rhosts or .shosts. */
256 snprintf(buf, sizeof buf, "%.500s/%.100s",
257 pw->pw_dir, rhosts_files[rhosts_file_index]);
258 if (stat(buf, &st) < 0)
259 continue; /* No such file. */
261 /* Make sure that the file is either owned by the user or by root,
262 and make sure it is not writable by anyone but the owner. This is
263 to help avoid novices accidentally allowing access to their account
265 if (options.strict_modes &&
266 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
267 (st.st_mode & 022) != 0))
269 log("Rhosts authentication refused for %.100s: bad modes for %.200s",
271 packet_send_debug("Bad file modes for %.200s", buf);
275 /* Check if we have been configured to ignore .rhosts and .shosts
277 if (options.ignore_rhosts)
279 packet_send_debug("Server has been configured to ignore %.100s.",
280 rhosts_files[rhosts_file_index]);
284 /* Check if authentication is permitted by the file. */
285 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name))
287 packet_send_debug("Accepted by %.100s.",
288 rhosts_files[rhosts_file_index]);
289 /* Restore the privileged uid. */
295 /* Rhosts authentication denied. */
296 /* Restore the privileged uid. */