Annotation of src/usr.bin/ssh/auth-rhosts.c, Revision 1.52
1.52 ! djm 1: /* $OpenBSD: auth-rhosts.c,v 1.51 2019/10/02 00:42:30 djm Exp $ */
1.1 deraadt 2: /*
1.10 deraadt 3: * Author: Tatu Ylonen <ylo@cs.hut.fi>
4: * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: * All rights reserved
6: * Rhosts authentication. This file contains code to check whether to admit
7: * the login based on rhosts authentication. This file also processes
8: * /etc/hosts.equiv.
1.13 markus 9: *
1.15 deraadt 10: * As far as I am concerned, the code I have written for this software
11: * can be used freely for any purpose. Any derived versions of this
12: * software must be clearly marked as such, and if the derived work is
13: * incompatible with the protocol description in the RFC file, it must be
14: * called by a name other than "ssh" or "Secure Shell".
1.10 deraadt 15: */
1.1 deraadt 16:
1.35 stevesk 17: #include <sys/types.h>
18: #include <sys/stat.h>
1.34 stevesk 19:
1.42 djm 20: #include <fcntl.h>
1.34 stevesk 21: #include <netgroup.h>
1.38 stevesk 22: #include <pwd.h>
1.40 stevesk 23: #include <stdio.h>
1.39 stevesk 24: #include <string.h>
1.41 deraadt 25: #include <stdarg.h>
1.43 dtucker 26: #include <unistd.h>
1.1 deraadt 27:
28: #include "packet.h"
29: #include "uidswap.h"
1.19 markus 30: #include "pathnames.h"
31: #include "log.h"
1.45 millert 32: #include "misc.h"
1.49 markus 33: #include "sshbuf.h"
34: #include "sshkey.h"
1.6 markus 35: #include "servconf.h"
1.19 markus 36: #include "canohost.h"
1.41 deraadt 37: #include "hostfile.h"
1.21 itojun 38: #include "auth.h"
1.1 deraadt 39:
1.23 markus 40: /* import */
41: extern ServerOptions options;
1.28 markus 42: extern int use_privsep;
1.23 markus 43:
1.11 markus 44: /*
45: * This function processes an rhosts-style file (.rhosts, .shosts, or
46: * /etc/hosts.equiv). This returns true if authentication can be granted
47: * based on the file, and returns zero otherwise.
48: */
1.1 deraadt 49:
1.24 itojun 50: static int
1.9 markus 51: check_rhosts_file(const char *filename, const char *hostname,
52: const char *ipaddr, const char *client_user,
53: const char *server_user)
1.1 deraadt 54: {
1.9 markus 55: FILE *f;
1.46 djm 56: #define RBUFLN 1024
57: char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
1.42 djm 58: int fd;
59: struct stat st;
1.1 deraadt 60:
1.9 markus 61: /* Open the .rhosts file, deny if unreadable */
1.42 djm 62: if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
1.9 markus 63: return 0;
1.42 djm 64: if (fstat(fd, &st) == -1) {
65: close(fd);
66: return 0;
67: }
68: if (!S_ISREG(st.st_mode)) {
69: logit("User %s hosts file %s is not a regular file",
70: server_user, filename);
71: close(fd);
72: return 0;
73: }
74: unset_nonblock(fd);
75: if ((f = fdopen(fd, "r")) == NULL) {
76: close(fd);
77: return 0;
78: }
1.9 markus 79: while (fgets(buf, sizeof(buf), f)) {
1.46 djm 80: /* All three must have length >= buf to avoid overflows. */
81: char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
82: char *host, *user, *cp;
1.9 markus 83: int negated;
84:
85: for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
86: ;
87: if (*cp == '#' || *cp == '\n' || !*cp)
88: continue;
89:
1.11 markus 90: /*
91: * NO_PLUS is supported at least on OSF/1. We skip it (we
92: * don't ever support the plus syntax).
93: */
1.9 markus 94: if (strncmp(cp, "NO_PLUS", 7) == 0)
95: continue;
96:
1.11 markus 97: /*
98: * This should be safe because each buffer is as big as the
99: * whole string, and thus cannot be overwritten.
100: */
1.30 itojun 101: switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
102: dummy)) {
1.9 markus 103: case 0:
1.28 markus 104: auth_debug_add("Found empty line in %.100s.", filename);
1.9 markus 105: continue;
106: case 1:
107: /* Host name only. */
108: strlcpy(userbuf, server_user, sizeof(userbuf));
109: break;
110: case 2:
111: /* Got both host and user name. */
112: break;
113: case 3:
1.28 markus 114: auth_debug_add("Found garbage in %.100s.", filename);
1.9 markus 115: continue;
116: default:
117: /* Weird... */
118: continue;
119: }
120:
121: host = hostbuf;
122: user = userbuf;
123: negated = 0;
124:
125: /* Process negated host names, or positive netgroups. */
126: if (host[0] == '-') {
127: negated = 1;
128: host++;
129: } else if (host[0] == '+')
130: host++;
131:
132: if (user[0] == '-') {
133: negated = 1;
134: user++;
135: } else if (user[0] == '+')
136: user++;
137:
138: /* Check for empty host/user names (particularly '+'). */
139: if (!host[0] || !user[0]) {
140: /* We come here if either was '+' or '-'. */
1.46 djm 141: auth_debug_add("Ignoring wild host/user names "
142: "in %.100s.", filename);
1.9 markus 143: continue;
144: }
145: /* Verify that host name matches. */
146: if (host[0] == '@') {
147: if (!innetgr(host + 1, hostname, NULL, NULL) &&
148: !innetgr(host + 1, ipaddr, NULL, NULL))
149: continue;
1.46 djm 150: } else if (strcasecmp(host, hostname) &&
151: strcmp(host, ipaddr) != 0)
1.9 markus 152: continue; /* Different hostname. */
153:
154: /* Verify that user name matches. */
155: if (user[0] == '@') {
156: if (!innetgr(user + 1, NULL, client_user, NULL))
157: continue;
158: } else if (strcmp(user, client_user) != 0)
159: continue; /* Different username. */
160:
161: /* Found the user and host. */
162: fclose(f);
163:
164: /* If the entry was negated, deny access. */
165: if (negated) {
1.28 markus 166: auth_debug_add("Matched negative entry in %.100s.",
1.33 djm 167: filename);
1.9 markus 168: return 0;
169: }
170: /* Accept authentication. */
171: return 1;
172: }
173:
174: /* Authentication using this file denied. */
175: fclose(f);
176: return 0;
1.1 deraadt 177: }
178:
1.11 markus 179: /*
180: * Tries to authenticate the user using the .shosts or .rhosts file. Returns
181: * true if authentication succeeds. If ignore_rhosts is true, only
182: * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
183: */
1.13 markus 184: int
1.48 markus 185: auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
1.23 markus 186: const char *ipaddr)
187: {
1.9 markus 188: char buf[1024];
189: struct stat st;
190: static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
1.17 markus 191: u_int rhosts_file_index;
1.9 markus 192:
1.23 markus 193: debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
194: client_user, hostname, ipaddr);
195:
1.9 markus 196: /* Switch to the user's uid. */
1.22 markus 197: temporarily_use_uid(pw);
1.11 markus 198: /*
1.46 djm 199: * Quick check: if the user has no .shosts or .rhosts files and
200: * no system hosts.equiv/shosts.equiv files exist then return
1.11 markus 201: * failure immediately without doing costly lookups from name
202: * servers.
203: */
1.9 markus 204: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
1.25 deraadt 205: rhosts_file_index++) {
1.9 markus 206: /* Check users .rhosts or .shosts. */
207: snprintf(buf, sizeof buf, "%.500s/%.100s",
208: pw->pw_dir, rhosts_files[rhosts_file_index]);
209: if (stat(buf, &st) >= 0)
210: break;
211: }
212: /* Switch back to privileged uid. */
213: restore_uid();
214:
1.46 djm 215: /*
216: * Deny if The user has no .shosts or .rhosts file and there
217: * are no system-wide files.
218: */
1.9 markus 219: if (!rhosts_files[rhosts_file_index] &&
1.50 deraadt 220: stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
221: stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
1.46 djm 222: debug3("%s: no hosts access files exist", __func__);
1.9 markus 223: return 0;
1.46 djm 224: }
1.9 markus 225:
1.46 djm 226: /*
227: * If not logging in as superuser, try /etc/hosts.equiv and
228: * shosts.equiv.
229: */
230: if (pw->pw_uid == 0)
231: debug3("%s: root user, ignoring system hosts files", __func__);
232: else {
1.25 deraadt 233: if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
234: client_user, pw->pw_name)) {
1.46 djm 235: auth_debug_add("Accepted for %.100s [%.100s] by "
236: "/etc/hosts.equiv.", hostname, ipaddr);
1.9 markus 237: return 1;
238: }
1.25 deraadt 239: if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
240: client_user, pw->pw_name)) {
1.46 djm 241: auth_debug_add("Accepted for %.100s [%.100s] by "
242: "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
1.9 markus 243: return 1;
244: }
245: }
1.46 djm 246:
1.11 markus 247: /*
248: * Check that the home directory is owned by root or the user, and is
249: * not group or world writable.
250: */
1.50 deraadt 251: if (stat(pw->pw_dir, &st) == -1) {
1.29 itojun 252: logit("Rhosts authentication refused for %.100s: "
1.28 markus 253: "no home directory %.200s", pw->pw_name, pw->pw_dir);
254: auth_debug_add("Rhosts authentication refused for %.100s: "
255: "no home directory %.200s", pw->pw_name, pw->pw_dir);
1.9 markus 256: return 0;
257: }
258: if (options.strict_modes &&
259: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
1.25 deraadt 260: (st.st_mode & 022) != 0)) {
1.29 itojun 261: logit("Rhosts authentication refused for %.100s: "
1.28 markus 262: "bad ownership or modes for home directory.", pw->pw_name);
263: auth_debug_add("Rhosts authentication refused for %.100s: "
264: "bad ownership or modes for home directory.", pw->pw_name);
1.9 markus 265: return 0;
266: }
267: /* Temporarily use the user's uid. */
1.22 markus 268: temporarily_use_uid(pw);
1.9 markus 269:
270: /* Check all .rhosts files (currently .shosts and .rhosts). */
271: for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
1.25 deraadt 272: rhosts_file_index++) {
1.9 markus 273: /* Check users .rhosts or .shosts. */
274: snprintf(buf, sizeof buf, "%.500s/%.100s",
275: pw->pw_dir, rhosts_files[rhosts_file_index]);
1.50 deraadt 276: if (stat(buf, &st) == -1)
1.9 markus 277: continue;
278:
1.11 markus 279: /*
280: * Make sure that the file is either owned by the user or by
281: * root, and make sure it is not writable by anyone but the
282: * owner. This is to help avoid novices accidentally
283: * allowing access to their account by anyone.
284: */
1.9 markus 285: if (options.strict_modes &&
286: ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
1.25 deraadt 287: (st.st_mode & 022) != 0)) {
1.29 itojun 288: logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
1.9 markus 289: pw->pw_name, buf);
1.28 markus 290: auth_debug_add("Bad file modes for %.200s", buf);
1.9 markus 291: continue;
292: }
1.46 djm 293: /*
294: * Check if we have been configured to ignore .rhosts
295: * and .shosts files.
296: */
1.52 ! djm 297: if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
! 298: (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
! 299: strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
1.46 djm 300: auth_debug_add("Server has been configured to "
301: "ignore %.100s.", rhosts_files[rhosts_file_index]);
1.9 markus 302: continue;
303: }
304: /* Check if authentication is permitted by the file. */
1.46 djm 305: if (check_rhosts_file(buf, hostname, ipaddr,
306: client_user, pw->pw_name)) {
1.28 markus 307: auth_debug_add("Accepted by %.100s.",
308: rhosts_files[rhosts_file_index]);
1.9 markus 309: /* Restore the privileged uid. */
310: restore_uid();
1.46 djm 311: auth_debug_add("Accepted host %s ip %s client_user "
312: "%s server_user %s", hostname, ipaddr,
313: client_user, pw->pw_name);
1.9 markus 314: return 1;
315: }
316: }
317:
318: /* Restore the privileged uid. */
319: restore_uid();
320: return 0;
1.1 deraadt 321: }
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