Annotation of src/usr.bin/ssh/auth-rhosts.c, Revision 1.10
1.1 deraadt 1: /*
1.10 ! deraadt 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: */
1.1 deraadt 17:
18: #include "includes.h"
1.10 ! deraadt 19: RCSID("$Id: auth-rhosts.c,v 1.9 1999/11/23 22:25:52 markus Exp $");
1.1 deraadt 20:
21: #include "packet.h"
22: #include "ssh.h"
23: #include "xmalloc.h"
24: #include "uidswap.h"
1.6 markus 25: #include "servconf.h"
1.1 deraadt 26:
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. */
30:
1.9 markus 31: int
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: /* Go through the file, checking every entry. */
45: 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;
48: int negated;
49:
50: for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
51: ;
52: if (*cp == '#' || *cp == '\n' || !*cp)
53: continue;
54:
55: /* NO_PLUS is supported at least on OSF/1. We skip it (we
56: don't ever support the plus syntax). */
57: if (strncmp(cp, "NO_PLUS", 7) == 0)
58: continue;
59:
60: /* This should be safe because each buffer is as big as
61: the whole string, and thus cannot be overwritten. */
62: switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
63: case 0:
64: packet_send_debug("Found empty line in %.100s.", filename);
65: continue;
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;
76: default:
77: /* Weird... */
78: continue;
79: }
80:
81: host = hostbuf;
82: user = userbuf;
83: negated = 0;
84:
85: /* Process negated host names, or positive netgroups. */
86: if (host[0] == '-') {
87: negated = 1;
88: host++;
89: } else if (host[0] == '+')
90: host++;
91:
92: if (user[0] == '-') {
93: negated = 1;
94: user++;
95: } else if (user[0] == '+')
96: user++;
97:
98: /* Check for empty host/user names (particularly '+'). */
99: if (!host[0] || !user[0]) {
100: /* We come here if either was '+' or '-'. */
101: packet_send_debug("Ignoring wild host/user names in %.100s.",
102: filename);
103: continue;
104: }
105: /* Verify that host name matches. */
106: if (host[0] == '@') {
107: if (!innetgr(host + 1, hostname, NULL, NULL) &&
108: !innetgr(host + 1, ipaddr, NULL, NULL))
109: continue;
110: } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
111: continue; /* Different hostname. */
112:
113: /* Verify that user name matches. */
114: if (user[0] == '@') {
115: if (!innetgr(user + 1, NULL, client_user, NULL))
116: continue;
117: } else if (strcmp(user, client_user) != 0)
118: continue; /* Different username. */
119:
120: /* Found the user and host. */
121: fclose(f);
122:
123: /* If the entry was negated, deny access. */
124: if (negated) {
125: packet_send_debug("Matched negative entry in %.100s.",
126: filename);
127: return 0;
128: }
129: /* Accept authentication. */
130: return 1;
131: }
132:
133: /* Authentication using this file denied. */
134: fclose(f);
135: return 0;
1.1 deraadt 136: }
137:
1.9 markus 138: /* Tries to authenticate the user using the .shosts or .rhosts file.
1.1 deraadt 139: Returns true if authentication succeeds. If ignore_rhosts is
140: true, only /etc/hosts.equiv will be considered (.rhosts and .shosts
141: are ignored). */
142:
1.9 markus 143: int
144: auth_rhosts(struct passwd *pw, const char *client_user)
1.1 deraadt 145: {
1.9 markus 146: extern ServerOptions options;
147: char buf[1024];
148: const char *hostname, *ipaddr;
149: struct stat st;
150: static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
151: unsigned int rhosts_file_index;
152:
153: /* Quick check: if the user has no .shosts or .rhosts files,
154: return failure immediately without doing costly lookups from
155: name servers. */
156: /* Switch to the user's uid. */
157: temporarily_use_uid(pw->pw_uid);
158: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
159: rhosts_file_index++) {
160: /* Check users .rhosts or .shosts. */
161: snprintf(buf, sizeof buf, "%.500s/%.100s",
162: pw->pw_dir, rhosts_files[rhosts_file_index]);
163: if (stat(buf, &st) >= 0)
164: break;
165: }
166: /* Switch back to privileged uid. */
167: restore_uid();
168:
169: /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
170: if (!rhosts_files[rhosts_file_index] &&
171: stat("/etc/hosts.equiv", &st) < 0 &&
172: stat(SSH_HOSTS_EQUIV, &st) < 0)
173: return 0;
174:
175: /* Get the name, address, and port of the remote host. */
176: hostname = get_canonical_hostname();
177: ipaddr = get_remote_ipaddr();
178:
179: /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
180: if (pw->pw_uid != 0) {
181: if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
182: pw->pw_name)) {
183: packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
184: hostname, ipaddr);
185: return 1;
186: }
187: if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
188: pw->pw_name)) {
189: packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
190: hostname, ipaddr, SSH_HOSTS_EQUIV);
191: return 1;
192: }
193: }
194: /* Check that the home directory is owned by root or the user, and
195: is not group or world writable. */
196: if (stat(pw->pw_dir, &st) < 0) {
197: log("Rhosts authentication refused for %.100s: no home directory %.200s",
198: pw->pw_name, pw->pw_dir);
199: packet_send_debug("Rhosts authentication refused for %.100: no home directory %.200s",
200: pw->pw_name, pw->pw_dir);
201: return 0;
202: }
203: if (options.strict_modes &&
204: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
205: (st.st_mode & 022) != 0)) {
206: log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
207: pw->pw_name);
208: packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
209: pw->pw_name);
210: return 0;
211: }
212: /* Temporarily use the user's uid. */
213: temporarily_use_uid(pw->pw_uid);
214:
215: /* Check all .rhosts files (currently .shosts and .rhosts). */
216: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
217: rhosts_file_index++) {
218: /* Check users .rhosts or .shosts. */
219: snprintf(buf, sizeof buf, "%.500s/%.100s",
220: pw->pw_dir, rhosts_files[rhosts_file_index]);
221: if (stat(buf, &st) < 0)
222: continue;
223:
224: /* Make sure that the file is either owned by the user or
225: by root, and make sure it is not writable by anyone but
226: the owner. This is to help avoid novices accidentally
227: allowing access to their account by anyone. */
228: if (options.strict_modes &&
229: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
230: (st.st_mode & 022) != 0)) {
231: log("Rhosts authentication refused for %.100s: bad modes for %.200s",
232: pw->pw_name, buf);
233: packet_send_debug("Bad file modes for %.200s", buf);
234: continue;
235: }
236: /* Check if we have been configured to ignore .rhosts and .shosts files. */
237: if (options.ignore_rhosts) {
238: packet_send_debug("Server has been configured to ignore %.100s.",
239: rhosts_files[rhosts_file_index]);
240: continue;
241: }
242: /* Check if authentication is permitted by the file. */
243: if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
244: packet_send_debug("Accepted by %.100s.",
245: rhosts_files[rhosts_file_index]);
246: /* Restore the privileged uid. */
247: restore_uid();
248: return 1;
249: }
250: }
251:
252: /* Restore the privileged uid. */
253: restore_uid();
254: return 0;
1.1 deraadt 255: }
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