325 lines
8.9 KiB
C
325 lines
8.9 KiB
C
/* $OpenBSD: auth-rhosts.c,v 1.49 2018/07/09 21:35:50 markus Exp $ */
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/*
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* Author: Tatu Ylonen <ylo@cs.hut.fi>
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* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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* All rights reserved
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* Rhosts authentication. This file contains code to check whether to admit
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* the login based on rhosts authentication. This file also processes
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* /etc/hosts.equiv.
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*
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* As far as I am concerned, the code I have written for this software
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* can be used freely for any purpose. Any derived versions of this
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* software must be clearly marked as such, and if the derived work is
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* incompatible with the protocol description in the RFC file, it must be
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* called by a name other than "ssh" or "Secure Shell".
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*/
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#include "includes.h"
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#include <sys/types.h>
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#include <sys/stat.h>
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#ifdef HAVE_NETGROUP_H
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# include <netgroup.h>
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#endif
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#include <pwd.h>
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#include <stdio.h>
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#include <string.h>
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#include <stdarg.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include "packet.h"
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#include "uidswap.h"
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#include "pathnames.h"
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#include "log.h"
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#include "misc.h"
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#include "sshbuf.h"
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#include "sshkey.h"
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#include "servconf.h"
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#include "canohost.h"
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#include "sshkey.h"
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#include "hostfile.h"
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#include "auth.h"
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/* import */
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extern ServerOptions options;
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extern int use_privsep;
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/*
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* This function processes an rhosts-style file (.rhosts, .shosts, or
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* /etc/hosts.equiv). This returns true if authentication can be granted
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* based on the file, and returns zero otherwise.
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*/
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static int
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check_rhosts_file(const char *filename, const char *hostname,
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const char *ipaddr, const char *client_user,
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const char *server_user)
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{
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FILE *f;
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#define RBUFLN 1024
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char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
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int fd;
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struct stat st;
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/* Open the .rhosts file, deny if unreadable */
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if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
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return 0;
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if (fstat(fd, &st) == -1) {
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close(fd);
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return 0;
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}
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if (!S_ISREG(st.st_mode)) {
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logit("User %s hosts file %s is not a regular file",
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server_user, filename);
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close(fd);
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return 0;
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}
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unset_nonblock(fd);
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if ((f = fdopen(fd, "r")) == NULL) {
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close(fd);
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return 0;
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}
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while (fgets(buf, sizeof(buf), f)) {
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/* All three must have length >= buf to avoid overflows. */
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char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
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char *host, *user, *cp;
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int negated;
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for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
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;
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if (*cp == '#' || *cp == '\n' || !*cp)
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continue;
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/*
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* NO_PLUS is supported at least on OSF/1. We skip it (we
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* don't ever support the plus syntax).
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*/
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if (strncmp(cp, "NO_PLUS", 7) == 0)
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continue;
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/*
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* This should be safe because each buffer is as big as the
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* whole string, and thus cannot be overwritten.
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*/
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switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
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dummy)) {
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case 0:
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auth_debug_add("Found empty line in %.100s.", filename);
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continue;
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case 1:
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/* Host name only. */
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strlcpy(userbuf, server_user, sizeof(userbuf));
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break;
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case 2:
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/* Got both host and user name. */
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break;
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case 3:
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auth_debug_add("Found garbage in %.100s.", filename);
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continue;
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default:
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/* Weird... */
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continue;
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}
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host = hostbuf;
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user = userbuf;
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negated = 0;
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/* Process negated host names, or positive netgroups. */
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if (host[0] == '-') {
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negated = 1;
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host++;
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} else if (host[0] == '+')
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host++;
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if (user[0] == '-') {
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negated = 1;
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user++;
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} else if (user[0] == '+')
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user++;
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/* Check for empty host/user names (particularly '+'). */
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if (!host[0] || !user[0]) {
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/* We come here if either was '+' or '-'. */
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auth_debug_add("Ignoring wild host/user names "
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"in %.100s.", filename);
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continue;
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}
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/* Verify that host name matches. */
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if (host[0] == '@') {
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if (!innetgr(host + 1, hostname, NULL, NULL) &&
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!innetgr(host + 1, ipaddr, NULL, NULL))
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continue;
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} else if (strcasecmp(host, hostname) &&
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strcmp(host, ipaddr) != 0)
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continue; /* Different hostname. */
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/* Verify that user name matches. */
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if (user[0] == '@') {
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if (!innetgr(user + 1, NULL, client_user, NULL))
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continue;
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} else if (strcmp(user, client_user) != 0)
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continue; /* Different username. */
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/* Found the user and host. */
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fclose(f);
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/* If the entry was negated, deny access. */
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if (negated) {
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auth_debug_add("Matched negative entry in %.100s.",
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filename);
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return 0;
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}
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/* Accept authentication. */
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return 1;
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}
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/* Authentication using this file denied. */
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fclose(f);
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return 0;
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}
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/*
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* Tries to authenticate the user using the .shosts or .rhosts file. Returns
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* true if authentication succeeds. If ignore_rhosts is true, only
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* /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
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*/
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int
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auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
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const char *ipaddr)
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{
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char buf[1024];
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struct stat st;
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static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
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u_int rhosts_file_index;
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debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
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client_user, hostname, ipaddr);
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/* Switch to the user's uid. */
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temporarily_use_uid(pw);
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/*
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* Quick check: if the user has no .shosts or .rhosts files and
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* no system hosts.equiv/shosts.equiv files exist then return
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* failure immediately without doing costly lookups from name
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* servers.
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*/
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for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
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rhosts_file_index++) {
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/* Check users .rhosts or .shosts. */
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snprintf(buf, sizeof buf, "%.500s/%.100s",
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pw->pw_dir, rhosts_files[rhosts_file_index]);
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if (stat(buf, &st) >= 0)
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break;
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}
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/* Switch back to privileged uid. */
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restore_uid();
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/*
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* Deny if The user has no .shosts or .rhosts file and there
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* are no system-wide files.
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*/
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if (!rhosts_files[rhosts_file_index] &&
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stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
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stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) {
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debug3("%s: no hosts access files exist", __func__);
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return 0;
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}
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/*
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* If not logging in as superuser, try /etc/hosts.equiv and
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* shosts.equiv.
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*/
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if (pw->pw_uid == 0)
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debug3("%s: root user, ignoring system hosts files", __func__);
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else {
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if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
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client_user, pw->pw_name)) {
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auth_debug_add("Accepted for %.100s [%.100s] by "
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"/etc/hosts.equiv.", hostname, ipaddr);
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return 1;
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}
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if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
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client_user, pw->pw_name)) {
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auth_debug_add("Accepted for %.100s [%.100s] by "
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"%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
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return 1;
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}
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}
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/*
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* Check that the home directory is owned by root or the user, and is
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* not group or world writable.
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*/
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if (stat(pw->pw_dir, &st) < 0) {
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logit("Rhosts authentication refused for %.100s: "
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"no home directory %.200s", pw->pw_name, pw->pw_dir);
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auth_debug_add("Rhosts authentication refused for %.100s: "
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"no home directory %.200s", pw->pw_name, pw->pw_dir);
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return 0;
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}
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if (options.strict_modes &&
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((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
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(st.st_mode & 022) != 0)) {
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logit("Rhosts authentication refused for %.100s: "
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"bad ownership or modes for home directory.", pw->pw_name);
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auth_debug_add("Rhosts authentication refused for %.100s: "
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"bad ownership or modes for home directory.", pw->pw_name);
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return 0;
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}
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/* Temporarily use the user's uid. */
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temporarily_use_uid(pw);
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/* Check all .rhosts files (currently .shosts and .rhosts). */
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for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
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rhosts_file_index++) {
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/* Check users .rhosts or .shosts. */
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snprintf(buf, sizeof buf, "%.500s/%.100s",
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pw->pw_dir, rhosts_files[rhosts_file_index]);
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if (stat(buf, &st) < 0)
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continue;
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/*
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* Make sure that the file is either owned by the user or by
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* root, and make sure it is not writable by anyone but the
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* owner. This is to help avoid novices accidentally
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* allowing access to their account by anyone.
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*/
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if (options.strict_modes &&
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((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
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(st.st_mode & 022) != 0)) {
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logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
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pw->pw_name, buf);
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auth_debug_add("Bad file modes for %.200s", buf);
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continue;
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}
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/*
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* Check if we have been configured to ignore .rhosts
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* and .shosts files.
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*/
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if (options.ignore_rhosts) {
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auth_debug_add("Server has been configured to "
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"ignore %.100s.", rhosts_files[rhosts_file_index]);
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continue;
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}
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/* Check if authentication is permitted by the file. */
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if (check_rhosts_file(buf, hostname, ipaddr,
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client_user, pw->pw_name)) {
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auth_debug_add("Accepted by %.100s.",
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rhosts_files[rhosts_file_index]);
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/* Restore the privileged uid. */
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restore_uid();
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auth_debug_add("Accepted host %s ip %s client_user "
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"%s server_user %s", hostname, ipaddr,
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client_user, pw->pw_name);
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return 1;
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}
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}
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/* Restore the privileged uid. */
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restore_uid();
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return 0;
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}
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