Annotation of src/usr.bin/ssh/auth-rhosts.c, Revision 1.9
1.1 deraadt 1: /*
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: */
17:
18: #include "includes.h"
1.9 ! markus 19: RCSID("$Id: auth-rhosts.c,v 1.8 1999/11/18 14:00:47 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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