Annotation of src/usr.bin/ssh/auth-rhosts.c, Revision 1.16
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"
1.16 ! markus 17: RCSID("$OpenBSD: auth-rhosts.c,v 1.15 2000/09/07 20:27:49 deraadt Exp $");
1.1 deraadt 18:
19: #include "packet.h"
20: #include "ssh.h"
21: #include "xmalloc.h"
22: #include "uidswap.h"
1.6 markus 23: #include "servconf.h"
1.1 deraadt 24:
1.11 markus 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: */
1.1 deraadt 30:
1.13 markus 31: int
1.9 markus 32: check_rhosts_file(const char *filename, const char *hostname,
33: const char *ipaddr, const char *client_user,
34: const char *server_user)
1.1 deraadt 35: {
1.9 markus 36: FILE *f;
37: char buf[1024]; /* Must not be larger than host, user, dummy below. */
1.1 deraadt 38:
1.9 markus 39: /* Open the .rhosts file, deny if unreadable */
40: f = fopen(filename, "r");
41: if (!f)
42: return 0;
43:
44: while (fgets(buf, sizeof(buf), f)) {
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:
1.11 markus 54: /*
55: * NO_PLUS is supported at least on OSF/1. We skip it (we
56: * don't ever support the plus syntax).
57: */
1.9 markus 58: if (strncmp(cp, "NO_PLUS", 7) == 0)
59: continue;
60:
1.11 markus 61: /*
62: * This should be safe because each buffer is as big as the
63: * whole string, and thus cannot be overwritten.
64: */
1.9 markus 65: switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
66: case 0:
67: packet_send_debug("Found empty line in %.100s.", filename);
68: continue;
69: case 1:
70: /* Host name only. */
71: strlcpy(userbuf, server_user, sizeof(userbuf));
72: break;
73: case 2:
74: /* Got both host and user name. */
75: break;
76: case 3:
77: packet_send_debug("Found garbage in %.100s.", filename);
78: continue;
79: default:
80: /* Weird... */
81: continue;
82: }
83:
84: host = hostbuf;
85: user = userbuf;
86: negated = 0;
87:
88: /* Process negated host names, or positive netgroups. */
89: if (host[0] == '-') {
90: negated = 1;
91: host++;
92: } else if (host[0] == '+')
93: host++;
94:
95: if (user[0] == '-') {
96: negated = 1;
97: user++;
98: } else if (user[0] == '+')
99: user++;
100:
101: /* Check for empty host/user names (particularly '+'). */
102: if (!host[0] || !user[0]) {
103: /* We come here if either was '+' or '-'. */
104: packet_send_debug("Ignoring wild host/user names in %.100s.",
105: filename);
106: continue;
107: }
108: /* Verify that host name matches. */
109: if (host[0] == '@') {
110: if (!innetgr(host + 1, hostname, NULL, NULL) &&
111: !innetgr(host + 1, ipaddr, NULL, NULL))
112: continue;
113: } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
114: continue; /* Different hostname. */
115:
116: /* Verify that user name matches. */
117: if (user[0] == '@') {
118: if (!innetgr(user + 1, NULL, client_user, NULL))
119: continue;
120: } else if (strcmp(user, client_user) != 0)
121: continue; /* Different username. */
122:
123: /* Found the user and host. */
124: fclose(f);
125:
126: /* If the entry was negated, deny access. */
127: if (negated) {
128: packet_send_debug("Matched negative entry in %.100s.",
129: filename);
130: return 0;
131: }
132: /* Accept authentication. */
133: return 1;
134: }
135:
136: /* Authentication using this file denied. */
137: fclose(f);
138: return 0;
1.1 deraadt 139: }
140:
1.11 markus 141: /*
142: * Tries to authenticate the user using the .shosts or .rhosts file. Returns
143: * true if authentication succeeds. If ignore_rhosts is true, only
144: * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
145: */
1.1 deraadt 146:
1.13 markus 147: int
1.9 markus 148: auth_rhosts(struct passwd *pw, const char *client_user)
1.1 deraadt 149: {
1.9 markus 150: extern ServerOptions options;
151: char buf[1024];
152: const char *hostname, *ipaddr;
153: struct stat st;
154: static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
155: unsigned int rhosts_file_index;
156:
1.16 ! markus 157: /* no user given */
! 158: if (pw == NULL)
! 159: return 0;
1.9 markus 160: /* Switch to the user's uid. */
161: temporarily_use_uid(pw->pw_uid);
1.11 markus 162: /*
163: * Quick check: if the user has no .shosts or .rhosts files, return
164: * failure immediately without doing costly lookups from name
165: * servers.
166: */
1.9 markus 167: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
168: rhosts_file_index++) {
169: /* Check users .rhosts or .shosts. */
170: snprintf(buf, sizeof buf, "%.500s/%.100s",
171: pw->pw_dir, rhosts_files[rhosts_file_index]);
172: if (stat(buf, &st) >= 0)
173: break;
174: }
175: /* Switch back to privileged uid. */
176: restore_uid();
177:
178: /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
179: if (!rhosts_files[rhosts_file_index] &&
180: stat("/etc/hosts.equiv", &st) < 0 &&
181: stat(SSH_HOSTS_EQUIV, &st) < 0)
182: return 0;
183:
184: hostname = get_canonical_hostname();
185: ipaddr = get_remote_ipaddr();
186:
187: /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
188: if (pw->pw_uid != 0) {
189: if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
190: pw->pw_name)) {
191: packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
192: hostname, ipaddr);
193: return 1;
194: }
195: if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
196: pw->pw_name)) {
197: packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
198: hostname, ipaddr, SSH_HOSTS_EQUIV);
199: return 1;
200: }
201: }
1.11 markus 202: /*
203: * Check that the home directory is owned by root or the user, and is
204: * not group or world writable.
205: */
1.9 markus 206: if (stat(pw->pw_dir, &st) < 0) {
207: log("Rhosts authentication refused for %.100s: no home directory %.200s",
208: pw->pw_name, pw->pw_dir);
1.12 markus 209: packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s",
1.9 markus 210: pw->pw_name, pw->pw_dir);
211: return 0;
212: }
213: if (options.strict_modes &&
214: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
215: (st.st_mode & 022) != 0)) {
216: log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
217: pw->pw_name);
218: packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
219: pw->pw_name);
220: return 0;
221: }
222: /* Temporarily use the user's uid. */
223: temporarily_use_uid(pw->pw_uid);
224:
225: /* Check all .rhosts files (currently .shosts and .rhosts). */
226: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
227: rhosts_file_index++) {
228: /* Check users .rhosts or .shosts. */
229: snprintf(buf, sizeof buf, "%.500s/%.100s",
230: pw->pw_dir, rhosts_files[rhosts_file_index]);
231: if (stat(buf, &st) < 0)
232: continue;
233:
1.11 markus 234: /*
235: * Make sure that the file is either owned by the user or by
236: * root, and make sure it is not writable by anyone but the
237: * owner. This is to help avoid novices accidentally
238: * allowing access to their account by anyone.
239: */
1.9 markus 240: if (options.strict_modes &&
241: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
242: (st.st_mode & 022) != 0)) {
243: log("Rhosts authentication refused for %.100s: bad modes for %.200s",
244: pw->pw_name, buf);
245: packet_send_debug("Bad file modes for %.200s", buf);
246: continue;
247: }
248: /* Check if we have been configured to ignore .rhosts and .shosts files. */
249: if (options.ignore_rhosts) {
250: packet_send_debug("Server has been configured to ignore %.100s.",
251: rhosts_files[rhosts_file_index]);
252: continue;
253: }
254: /* Check if authentication is permitted by the file. */
255: if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
256: packet_send_debug("Accepted by %.100s.",
257: rhosts_files[rhosts_file_index]);
258: /* Restore the privileged uid. */
259: restore_uid();
260: return 1;
261: }
262: }
263:
264: /* Restore the privileged uid. */
265: restore_uid();
266: return 0;
1.1 deraadt 267: }
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