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authorDamien Miller <djm@mindrot.org>1999-10-27 13:42:43 +1000
committerDamien Miller <djm@mindrot.org>1999-10-27 13:42:43 +1000
commitd4a8b7e34dd619a4debf9a206c81db26d1402ea6 (patch)
treea47d770a2f790f40d18b0982d4e55fa7cfb1fa3b /auth-rhosts.c
Initial revision
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+/*
+
+auth-rhosts.c
+
+Author: Tatu Ylonen <ylo@cs.hut.fi>
+
+Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ All rights reserved
+
+Created: Fri Mar 17 05:12:18 1995 ylo
+
+Rhosts authentication. This file contains code to check whether to admit
+the login based on rhosts authentication. This file also processes
+/etc/hosts.equiv.
+
+*/
+
+#include "includes.h"
+RCSID("$Id: auth-rhosts.c,v 1.1 1999/10/27 03:42:43 damien Exp $");
+
+#include "packet.h"
+#include "ssh.h"
+#include "xmalloc.h"
+#include "uidswap.h"
+
+/* 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. */
+
+int check_rhosts_file(const char *filename, const char *hostname,
+ const char *ipaddr, const char *client_user,
+ const char *server_user)
+{
+ FILE *f;
+ char buf[1024]; /* Must not be larger than host, user, dummy below. */
+
+ /* Open the .rhosts file. */
+ f = fopen(filename, "r");
+ if (!f)
+ return 0; /* Cannot read the .rhosts - deny access. */
+
+ /* Go through the file, checking every entry. */
+ while (fgets(buf, sizeof(buf), f))
+ {
+ /* All three must be at least as big as buf to avoid overflows. */
+ char hostbuf[1024], userbuf[1024], dummy[1024], *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, "%s %s %s", hostbuf, userbuf, dummy))
+ {
+ case 0:
+ packet_send_debug("Found empty line in %.100s.", filename);
+ continue; /* Empty line? */
+ case 1:
+ /* Host name only. */
+ strlcpy(userbuf, server_user, sizeof(userbuf));
+ break;
+ case 2:
+ /* Got both host and user name. */
+ break;
+ case 3:
+ packet_send_debug("Found garbage in %.100s.", filename);
+ continue; /* Extra garbage */
+ default:
+ continue; /* Weird... */
+ }
+
+ 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 '-'. */
+ packet_send_debug("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)
+ {
+ packet_send_debug("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_rhosts(struct passwd *pw, const char *client_user,
+ int ignore_rhosts, int strict_modes)
+{
+ char buf[1024];
+ const char *hostname, *ipaddr;
+ int port;
+ struct stat st;
+ static const char *rhosts_files[] = { ".shosts", ".rhosts", NULL };
+ unsigned int rhosts_file_index;
+
+ /* Quick check: if the user has no .shosts or .rhosts files, return failure
+ immediately without doing costly lookups from name servers. */
+ /* Switch to the user's uid. */
+ temporarily_use_uid(pw->pw_uid);
+ 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();
+
+ if (!rhosts_files[rhosts_file_index] && stat("/etc/hosts.equiv", &st) < 0 &&
+ stat(SSH_HOSTS_EQUIV, &st) < 0)
+ return 0; /* The user has no .shosts or .rhosts file and there are no
+ system-wide files. */
+
+ /* Get the name, address, and port of the remote host. */
+ hostname = get_canonical_hostname();
+ ipaddr = get_remote_ipaddr();
+ port = get_remote_port();
+
+ /* Check that the connection comes from a privileged port.
+ Rhosts authentication only makes sense for priviledged programs.
+ Of course, if the intruder has root access on his local machine,
+ he can connect from any port. So do not use .rhosts
+ authentication from machines that you do not trust. */
+ if (port >= IPPORT_RESERVED ||
+ port < IPPORT_RESERVED / 2)
+ {
+ log("Connection from %.100s from nonpriviledged port %d",
+ hostname, port);
+ packet_send_debug("Your ssh client is not running as root.");
+ return 0;
+ }
+
+ /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
+ if (pw->pw_uid != 0)
+ {
+ if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
+ pw->pw_name))
+ {
+ packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
+ hostname, ipaddr);
+ return 1;
+ }
+ if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
+ pw->pw_name))
+ {
+ packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
+ hostname, ipaddr, 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)
+ {
+ log("Rhosts authentication refused for %.100: no home directory %.200s",
+ pw->pw_name, pw->pw_dir);
+ packet_send_debug("Rhosts authentication refused for %.100: no home directory %.200s",
+ pw->pw_name, pw->pw_dir);
+ return 0;
+ }
+ if (strict_modes &&
+ ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+ (st.st_mode & 022) != 0))
+ {
+ log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
+ pw->pw_name);
+ packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
+ pw->pw_name);
+ return 0;
+ }
+
+ /* Check all .rhosts files (currently .shosts and .rhosts). */
+ /* Temporarily use the user's uid. */
+ temporarily_use_uid(pw->pw_uid);
+ 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; /* No such file. */
+
+ /* 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 (strict_modes &&
+ ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+ (st.st_mode & 022) != 0))
+ {
+ log("Rhosts authentication refused for %.100s: bad modes for %.200s",
+ pw->pw_name, buf);
+ packet_send_debug("Bad file modes for %.200s", buf);
+ continue;
+ }
+
+ /* Check if we have been configured to ignore .rhosts and .shosts
+ files. */
+ if (ignore_rhosts)
+ {
+ packet_send_debug("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))
+ {
+ packet_send_debug("Accepted by %.100s.",
+ rhosts_files[rhosts_file_index]);
+ /* Restore the privileged uid. */
+ restore_uid();
+ return 1;
+ }
+ }
+
+ /* Rhosts authentication denied. */
+ /* Restore the privileged uid. */
+ restore_uid();
+ return 0;
+}