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-rw-r--r--auth-rhosts.c324
1 files changed, 324 insertions, 0 deletions
diff --git a/auth-rhosts.c b/auth-rhosts.c
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+/* $OpenBSD: auth-rhosts.c,v 1.49 2018/07/09 21:35:50 markus Exp $ */
+/*
+ * Author: Tatu Ylonen <ylo@cs.hut.fi>
+ * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ * All rights reserved
+ * Rhosts authentication. This file contains code to check whether to admit
+ * the login based on rhosts authentication. This file also processes
+ * /etc/hosts.equiv.
+ *
+ * As far as I am concerned, the code I have written for this software
+ * can be used freely for any purpose. Any derived versions of this
+ * software must be clearly marked as such, and if the derived work is
+ * incompatible with the protocol description in the RFC file, it must be
+ * called by a name other than "ssh" or "Secure Shell".
+ */
+
+#include "includes.h"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#ifdef HAVE_NETGROUP_H
+# include <netgroup.h>
+#endif
+#include <pwd.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "packet.h"
+#include "uidswap.h"
+#include "pathnames.h"
+#include "log.h"
+#include "misc.h"
+#include "sshbuf.h"
+#include "sshkey.h"
+#include "servconf.h"
+#include "canohost.h"
+#include "sshkey.h"
+#include "hostfile.h"
+#include "auth.h"
+
+/* import */
+extern ServerOptions options;
+extern int use_privsep;
+
+/*
+ * This function processes an rhosts-style file (.rhosts, .shosts, or
+ * /etc/hosts.equiv). This returns true if authentication can be granted
+ * based on the file, and returns zero otherwise.
+ */
+
+static int
+check_rhosts_file(const char *filename, const char *hostname,
+ const char *ipaddr, const char *client_user,
+ const char *server_user)
+{
+ FILE *f;
+#define RBUFLN 1024
+ char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
+ int fd;
+ struct stat st;
+
+ /* Open the .rhosts file, deny if unreadable */
+ if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
+ return 0;
+ if (fstat(fd, &st) == -1) {
+ close(fd);
+ return 0;
+ }
+ if (!S_ISREG(st.st_mode)) {
+ logit("User %s hosts file %s is not a regular file",
+ server_user, filename);
+ close(fd);
+ return 0;
+ }
+ unset_nonblock(fd);
+ if ((f = fdopen(fd, "r")) == NULL) {
+ close(fd);
+ return 0;
+ }
+ while (fgets(buf, sizeof(buf), f)) {
+ /* All three must have length >= buf to avoid overflows. */
+ char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
+ char *host, *user, *cp;
+ int negated;
+
+ for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
+ ;
+ if (*cp == '#' || *cp == '\n' || !*cp)
+ continue;
+
+ /*
+ * NO_PLUS is supported at least on OSF/1. We skip it (we
+ * don't ever support the plus syntax).
+ */
+ if (strncmp(cp, "NO_PLUS", 7) == 0)
+ continue;
+
+ /*
+ * This should be safe because each buffer is as big as the
+ * whole string, and thus cannot be overwritten.
+ */
+ switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
+ dummy)) {
+ case 0:
+ auth_debug_add("Found empty line in %.100s.", filename);
+ continue;
+ case 1:
+ /* Host name only. */
+ strlcpy(userbuf, server_user, sizeof(userbuf));
+ break;
+ case 2:
+ /* Got both host and user name. */
+ break;
+ case 3:
+ auth_debug_add("Found garbage in %.100s.", filename);
+ continue;
+ default:
+ /* Weird... */
+ continue;
+ }
+
+ host = hostbuf;
+ user = userbuf;
+ negated = 0;
+
+ /* Process negated host names, or positive netgroups. */
+ if (host[0] == '-') {
+ negated = 1;
+ host++;
+ } else if (host[0] == '+')
+ host++;
+
+ if (user[0] == '-') {
+ negated = 1;
+ user++;
+ } else if (user[0] == '+')
+ user++;
+
+ /* Check for empty host/user names (particularly '+'). */
+ if (!host[0] || !user[0]) {
+ /* We come here if either was '+' or '-'. */
+ auth_debug_add("Ignoring wild host/user names "
+ "in %.100s.", filename);
+ continue;
+ }
+ /* Verify that host name matches. */
+ if (host[0] == '@') {
+ if (!innetgr(host + 1, hostname, NULL, NULL) &&
+ !innetgr(host + 1, ipaddr, NULL, NULL))
+ continue;
+ } else if (strcasecmp(host, hostname) &&
+ strcmp(host, ipaddr) != 0)
+ continue; /* Different hostname. */
+
+ /* Verify that user name matches. */
+ if (user[0] == '@') {
+ if (!innetgr(user + 1, NULL, client_user, NULL))
+ continue;
+ } else if (strcmp(user, client_user) != 0)
+ continue; /* Different username. */
+
+ /* Found the user and host. */
+ fclose(f);
+
+ /* If the entry was negated, deny access. */
+ if (negated) {
+ auth_debug_add("Matched negative entry in %.100s.",
+ filename);
+ return 0;
+ }
+ /* Accept authentication. */
+ return 1;
+ }
+
+ /* Authentication using this file denied. */
+ fclose(f);
+ return 0;
+}
+
+/*
+ * Tries to authenticate the user using the .shosts or .rhosts file. Returns
+ * true if authentication succeeds. If ignore_rhosts is true, only
+ * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
+ */
+int
+auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
+ const char *ipaddr)
+{
+ char buf[1024];
+ struct stat st;
+ static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
+ u_int rhosts_file_index;
+
+ debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
+ client_user, hostname, ipaddr);
+
+ /* Switch to the user's uid. */
+ temporarily_use_uid(pw);
+ /*
+ * Quick check: if the user has no .shosts or .rhosts files and
+ * no system hosts.equiv/shosts.equiv files exist then return
+ * failure immediately without doing costly lookups from name
+ * servers.
+ */
+ for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
+ rhosts_file_index++) {
+ /* Check users .rhosts or .shosts. */
+ snprintf(buf, sizeof buf, "%.500s/%.100s",
+ pw->pw_dir, rhosts_files[rhosts_file_index]);
+ if (stat(buf, &st) >= 0)
+ break;
+ }
+ /* Switch back to privileged uid. */
+ restore_uid();
+
+ /*
+ * Deny if The user has no .shosts or .rhosts file and there
+ * are no system-wide files.
+ */
+ if (!rhosts_files[rhosts_file_index] &&
+ stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
+ stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) {
+ debug3("%s: no hosts access files exist", __func__);
+ return 0;
+ }
+
+ /*
+ * If not logging in as superuser, try /etc/hosts.equiv and
+ * shosts.equiv.
+ */
+ if (pw->pw_uid == 0)
+ debug3("%s: root user, ignoring system hosts files", __func__);
+ else {
+ if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
+ client_user, pw->pw_name)) {
+ auth_debug_add("Accepted for %.100s [%.100s] by "
+ "/etc/hosts.equiv.", hostname, ipaddr);
+ return 1;
+ }
+ if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
+ client_user, pw->pw_name)) {
+ auth_debug_add("Accepted for %.100s [%.100s] by "
+ "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
+ return 1;
+ }
+ }
+
+ /*
+ * Check that the home directory is owned by root or the user, and is
+ * not group or world writable.
+ */
+ if (stat(pw->pw_dir, &st) < 0) {
+ logit("Rhosts authentication refused for %.100s: "
+ "no home directory %.200s", pw->pw_name, pw->pw_dir);
+ auth_debug_add("Rhosts authentication refused for %.100s: "
+ "no home directory %.200s", pw->pw_name, pw->pw_dir);
+ return 0;
+ }
+ if (options.strict_modes &&
+ ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+ (st.st_mode & 022) != 0)) {
+ logit("Rhosts authentication refused for %.100s: "
+ "bad ownership or modes for home directory.", pw->pw_name);
+ auth_debug_add("Rhosts authentication refused for %.100s: "
+ "bad ownership or modes for home directory.", pw->pw_name);
+ return 0;
+ }
+ /* Temporarily use the user's uid. */
+ temporarily_use_uid(pw);
+
+ /* Check all .rhosts files (currently .shosts and .rhosts). */
+ for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
+ rhosts_file_index++) {
+ /* Check users .rhosts or .shosts. */
+ snprintf(buf, sizeof buf, "%.500s/%.100s",
+ pw->pw_dir, rhosts_files[rhosts_file_index]);
+ if (stat(buf, &st) < 0)
+ continue;
+
+ /*
+ * Make sure that the file is either owned by the user or by
+ * root, and make sure it is not writable by anyone but the
+ * owner. This is to help avoid novices accidentally
+ * allowing access to their account by anyone.
+ */
+ if (options.strict_modes &&
+ ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+ (st.st_mode & 022) != 0)) {
+ logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
+ pw->pw_name, buf);
+ auth_debug_add("Bad file modes for %.200s", buf);
+ continue;
+ }
+ /*
+ * Check if we have been configured to ignore .rhosts
+ * and .shosts files.
+ */
+ if (options.ignore_rhosts) {
+ auth_debug_add("Server has been configured to "
+ "ignore %.100s.", rhosts_files[rhosts_file_index]);
+ continue;
+ }
+ /* Check if authentication is permitted by the file. */
+ if (check_rhosts_file(buf, hostname, ipaddr,
+ client_user, pw->pw_name)) {
+ auth_debug_add("Accepted by %.100s.",
+ rhosts_files[rhosts_file_index]);
+ /* Restore the privileged uid. */
+ restore_uid();
+ auth_debug_add("Accepted host %s ip %s client_user "
+ "%s server_user %s", hostname, ipaddr,
+ client_user, pw->pw_name);
+ return 1;
+ }
+ }
+
+ /* Restore the privileged uid. */
+ restore_uid();
+ return 0;
+}
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