Annotation of src/usr.bin/ssh/auth-rhosts.c, Revision 1.19
1.1 deraadt 1: /*
1.10 deraadt 2: * Author: Tatu Ylonen <ylo@cs.hut.fi>
3: * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: * All rights reserved
5: * Rhosts authentication. This file contains code to check whether to admit
6: * the login based on rhosts authentication. This file also processes
7: * /etc/hosts.equiv.
1.13 markus 8: *
1.15 deraadt 9: * As far as I am concerned, the code I have written for this software
10: * can be used freely for any purpose. Any derived versions of this
11: * software must be clearly marked as such, and if the derived work is
12: * incompatible with the protocol description in the RFC file, it must be
13: * called by a name other than "ssh" or "Secure Shell".
1.10 deraadt 14: */
1.1 deraadt 15:
16: #include "includes.h"
1.19 ! markus 17: RCSID("$OpenBSD: auth-rhosts.c,v 1.18 2001/01/19 15:55:10 markus Exp $");
1.1 deraadt 18:
19: #include "packet.h"
20: #include "xmalloc.h"
21: #include "uidswap.h"
1.19 ! markus 22: #include "pathnames.h"
! 23: #include "log.h"
1.6 markus 24: #include "servconf.h"
1.19 ! markus 25: #include "canohost.h"
1.1 deraadt 26:
1.11 markus 27: /*
28: * This function processes an rhosts-style file (.rhosts, .shosts, or
29: * /etc/hosts.equiv). This returns true if authentication can be granted
30: * based on the file, and returns zero otherwise.
31: */
1.1 deraadt 32:
1.13 markus 33: int
1.9 markus 34: check_rhosts_file(const char *filename, const char *hostname,
35: const char *ipaddr, const char *client_user,
36: const char *server_user)
1.1 deraadt 37: {
1.9 markus 38: FILE *f;
39: char buf[1024]; /* Must not be larger than host, user, dummy below. */
1.1 deraadt 40:
1.9 markus 41: /* Open the .rhosts file, deny if unreadable */
42: f = fopen(filename, "r");
43: if (!f)
44: return 0;
45:
46: while (fgets(buf, sizeof(buf), f)) {
47: /* All three must be at least as big as buf to avoid overflows. */
48: char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
49: int negated;
50:
51: for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
52: ;
53: if (*cp == '#' || *cp == '\n' || !*cp)
54: continue;
55:
1.11 markus 56: /*
57: * NO_PLUS is supported at least on OSF/1. We skip it (we
58: * don't ever support the plus syntax).
59: */
1.9 markus 60: if (strncmp(cp, "NO_PLUS", 7) == 0)
61: continue;
62:
1.11 markus 63: /*
64: * This should be safe because each buffer is as big as the
65: * whole string, and thus cannot be overwritten.
66: */
1.9 markus 67: switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
68: case 0:
69: packet_send_debug("Found empty line in %.100s.", filename);
70: continue;
71: case 1:
72: /* Host name only. */
73: strlcpy(userbuf, server_user, sizeof(userbuf));
74: break;
75: case 2:
76: /* Got both host and user name. */
77: break;
78: case 3:
79: packet_send_debug("Found garbage in %.100s.", filename);
80: continue;
81: default:
82: /* Weird... */
83: continue;
84: }
85:
86: host = hostbuf;
87: user = userbuf;
88: negated = 0;
89:
90: /* Process negated host names, or positive netgroups. */
91: if (host[0] == '-') {
92: negated = 1;
93: host++;
94: } else if (host[0] == '+')
95: host++;
96:
97: if (user[0] == '-') {
98: negated = 1;
99: user++;
100: } else if (user[0] == '+')
101: user++;
102:
103: /* Check for empty host/user names (particularly '+'). */
104: if (!host[0] || !user[0]) {
105: /* We come here if either was '+' or '-'. */
106: packet_send_debug("Ignoring wild host/user names in %.100s.",
107: filename);
108: continue;
109: }
110: /* Verify that host name matches. */
111: if (host[0] == '@') {
112: if (!innetgr(host + 1, hostname, NULL, NULL) &&
113: !innetgr(host + 1, ipaddr, NULL, NULL))
114: continue;
115: } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
116: continue; /* Different hostname. */
117:
118: /* Verify that user name matches. */
119: if (user[0] == '@') {
120: if (!innetgr(user + 1, NULL, client_user, NULL))
121: continue;
122: } else if (strcmp(user, client_user) != 0)
123: continue; /* Different username. */
124:
125: /* Found the user and host. */
126: fclose(f);
127:
128: /* If the entry was negated, deny access. */
129: if (negated) {
130: packet_send_debug("Matched negative entry in %.100s.",
131: filename);
132: return 0;
133: }
134: /* Accept authentication. */
135: return 1;
136: }
137:
138: /* Authentication using this file denied. */
139: fclose(f);
140: return 0;
1.1 deraadt 141: }
142:
1.11 markus 143: /*
144: * Tries to authenticate the user using the .shosts or .rhosts file. Returns
145: * true if authentication succeeds. If ignore_rhosts is true, only
146: * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
147: */
1.1 deraadt 148:
1.13 markus 149: int
1.9 markus 150: auth_rhosts(struct passwd *pw, const char *client_user)
1.1 deraadt 151: {
1.9 markus 152: extern ServerOptions options;
153: char buf[1024];
154: const char *hostname, *ipaddr;
155: struct stat st;
156: static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
1.17 markus 157: u_int rhosts_file_index;
1.9 markus 158:
1.16 markus 159: /* no user given */
160: if (pw == NULL)
161: return 0;
1.9 markus 162: /* Switch to the user's uid. */
163: temporarily_use_uid(pw->pw_uid);
1.11 markus 164: /*
165: * Quick check: if the user has no .shosts or .rhosts files, return
166: * failure immediately without doing costly lookups from name
167: * servers.
168: */
1.9 markus 169: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
170: rhosts_file_index++) {
171: /* Check users .rhosts or .shosts. */
172: snprintf(buf, sizeof buf, "%.500s/%.100s",
173: pw->pw_dir, rhosts_files[rhosts_file_index]);
174: if (stat(buf, &st) >= 0)
175: break;
176: }
177: /* Switch back to privileged uid. */
178: restore_uid();
179:
180: /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
181: if (!rhosts_files[rhosts_file_index] &&
1.18 markus 182: stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
183: stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
1.9 markus 184: return 0;
185:
186: hostname = get_canonical_hostname();
187: ipaddr = get_remote_ipaddr();
188:
189: /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
190: if (pw->pw_uid != 0) {
191: if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
192: pw->pw_name)) {
193: packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
194: hostname, ipaddr);
195: return 1;
196: }
1.18 markus 197: if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
1.9 markus 198: pw->pw_name)) {
199: packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
1.18 markus 200: hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
1.9 markus 201: return 1;
202: }
203: }
1.11 markus 204: /*
205: * Check that the home directory is owned by root or the user, and is
206: * not group or world writable.
207: */
1.9 markus 208: if (stat(pw->pw_dir, &st) < 0) {
209: log("Rhosts authentication refused for %.100s: no home directory %.200s",
210: pw->pw_name, pw->pw_dir);
1.12 markus 211: packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s",
1.9 markus 212: pw->pw_name, pw->pw_dir);
213: return 0;
214: }
215: if (options.strict_modes &&
216: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
217: (st.st_mode & 022) != 0)) {
218: log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
219: pw->pw_name);
220: packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
221: pw->pw_name);
222: return 0;
223: }
224: /* Temporarily use the user's uid. */
225: temporarily_use_uid(pw->pw_uid);
226:
227: /* Check all .rhosts files (currently .shosts and .rhosts). */
228: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
229: rhosts_file_index++) {
230: /* Check users .rhosts or .shosts. */
231: snprintf(buf, sizeof buf, "%.500s/%.100s",
232: pw->pw_dir, rhosts_files[rhosts_file_index]);
233: if (stat(buf, &st) < 0)
234: continue;
235:
1.11 markus 236: /*
237: * Make sure that the file is either owned by the user or by
238: * root, and make sure it is not writable by anyone but the
239: * owner. This is to help avoid novices accidentally
240: * allowing access to their account by anyone.
241: */
1.9 markus 242: if (options.strict_modes &&
243: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
244: (st.st_mode & 022) != 0)) {
245: log("Rhosts authentication refused for %.100s: bad modes for %.200s",
246: pw->pw_name, buf);
247: packet_send_debug("Bad file modes for %.200s", buf);
248: continue;
249: }
250: /* Check if we have been configured to ignore .rhosts and .shosts files. */
251: if (options.ignore_rhosts) {
252: packet_send_debug("Server has been configured to ignore %.100s.",
253: rhosts_files[rhosts_file_index]);
254: continue;
255: }
256: /* Check if authentication is permitted by the file. */
257: if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
258: packet_send_debug("Accepted by %.100s.",
259: rhosts_files[rhosts_file_index]);
260: /* Restore the privileged uid. */
261: restore_uid();
262: return 1;
263: }
264: }
265:
266: /* Restore the privileged uid. */
267: restore_uid();
268: return 0;
1.1 deraadt 269: }
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