diff options
Diffstat (limited to 'auth.c')
| -rw-r--r-- | auth.c | 705 |
1 files changed, 705 insertions, 0 deletions
@@ -0,0 +1,705 @@ +/* $OpenBSD: auth.c,v 1.94 2011/05/23 03:33:38 djm Exp $ */ +/* + * Copyright (c) 2000 Markus Friedl. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +#include "includes.h" + +#include <sys/types.h> +#include <sys/stat.h> +#include <sys/param.h> + +#include <netinet/in.h> + +#include <errno.h> +#include <fcntl.h> +#ifdef HAVE_PATHS_H +# include <paths.h> +#endif +#include <pwd.h> +#ifdef HAVE_LOGIN_H +#include <login.h> +#endif +#ifdef USE_SHADOW +#include <shadow.h> +#endif +#ifdef HAVE_LIBGEN_H +#include <libgen.h> +#endif +#include <stdarg.h> +#include <stdio.h> +#include <string.h> +#include <unistd.h> + +#include "xmalloc.h" +#include "match.h" +#include "groupaccess.h" +#include "log.h" +#include "buffer.h" +#include "servconf.h" +#include "key.h" +#include "hostfile.h" +#include "auth.h" +#include "auth-options.h" +#include "canohost.h" +#include "uidswap.h" +#include "misc.h" +#include "packet.h" +#include "loginrec.h" +#ifdef GSSAPI +#include "ssh-gss.h" +#endif +#include "authfile.h" +#include "monitor_wrap.h" + +/* import */ +extern ServerOptions options; +extern int use_privsep; +extern Buffer loginmsg; +extern struct passwd *privsep_pw; + +/* Debugging messages */ +Buffer auth_debug; +int auth_debug_init; + +/* + * Check if the user is allowed to log in via ssh. If user is listed + * in DenyUsers or one of user's groups is listed in DenyGroups, false + * will be returned. If AllowUsers isn't empty and user isn't listed + * there, or if AllowGroups isn't empty and one of user's groups isn't + * listed there, false will be returned. + * If the user's shell is not executable, false will be returned. + * Otherwise true is returned. + */ +int +allowed_user(struct passwd * pw) +{ + struct stat st; + const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL; + u_int i; +#ifdef USE_SHADOW + struct spwd *spw = NULL; +#endif + + /* Shouldn't be called if pw is NULL, but better safe than sorry... */ + if (!pw || !pw->pw_name) + return 0; + +#ifdef USE_SHADOW + if (!options.use_pam) + spw = getspnam(pw->pw_name); +#ifdef HAS_SHADOW_EXPIRE + if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw)) + return 0; +#endif /* HAS_SHADOW_EXPIRE */ +#endif /* USE_SHADOW */ + + /* grab passwd field for locked account check */ + passwd = pw->pw_passwd; +#ifdef USE_SHADOW + if (spw != NULL) +#ifdef USE_LIBIAF + passwd = get_iaf_password(pw); +#else + passwd = spw->sp_pwdp; +#endif /* USE_LIBIAF */ +#endif + + /* check for locked account */ + if (!options.use_pam && passwd && *passwd) { + int locked = 0; + +#ifdef LOCKED_PASSWD_STRING + if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0) + locked = 1; +#endif +#ifdef LOCKED_PASSWD_PREFIX + if (strncmp(passwd, LOCKED_PASSWD_PREFIX, + strlen(LOCKED_PASSWD_PREFIX)) == 0) + locked = 1; +#endif +#ifdef LOCKED_PASSWD_SUBSTR + if (strstr(passwd, LOCKED_PASSWD_SUBSTR)) + locked = 1; +#endif +#ifdef USE_LIBIAF + free((void *) passwd); +#endif /* USE_LIBIAF */ + if (locked) { + logit("User %.100s not allowed because account is locked", + pw->pw_name); + return 0; + } + } + + /* + * Deny if shell does not exist or is not executable unless we + * are chrooting. + */ + if (options.chroot_directory == NULL || + strcasecmp(options.chroot_directory, "none") == 0) { + char *shell = xstrdup((pw->pw_shell[0] == '\0') ? + _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ + + if (stat(shell, &st) != 0) { + logit("User %.100s not allowed because shell %.100s " + "does not exist", pw->pw_name, shell); + xfree(shell); + return 0; + } + if (S_ISREG(st.st_mode) == 0 || + (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { + logit("User %.100s not allowed because shell %.100s " + "is not executable", pw->pw_name, shell); + xfree(shell); + return 0; + } + xfree(shell); + } + + if (options.num_deny_users > 0 || options.num_allow_users > 0 || + options.num_deny_groups > 0 || options.num_allow_groups > 0) { + hostname = get_canonical_hostname(options.use_dns); + ipaddr = get_remote_ipaddr(); + } + + /* Return false if user is listed in DenyUsers */ + if (options.num_deny_users > 0) { + for (i = 0; i < options.num_deny_users; i++) + if (match_user(pw->pw_name, hostname, ipaddr, + options.deny_users[i])) { + logit("User %.100s from %.100s not allowed " + "because listed in DenyUsers", + pw->pw_name, hostname); + return 0; + } + } + /* Return false if AllowUsers isn't empty and user isn't listed there */ + if (options.num_allow_users > 0) { + for (i = 0; i < options.num_allow_users; i++) + if (match_user(pw->pw_name, hostname, ipaddr, + options.allow_users[i])) + break; + /* i < options.num_allow_users iff we break for loop */ + if (i >= options.num_allow_users) { + logit("User %.100s from %.100s not allowed because " + "not listed in AllowUsers", pw->pw_name, hostname); + return 0; + } + } + if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { + /* Get the user's group access list (primary and supplementary) */ + if (ga_init(pw->pw_name, pw->pw_gid) == 0) { + logit("User %.100s from %.100s not allowed because " + "not in any group", pw->pw_name, hostname); + return 0; + } + + /* Return false if one of user's groups is listed in DenyGroups */ + if (options.num_deny_groups > 0) + if (ga_match(options.deny_groups, + options.num_deny_groups)) { + ga_free(); + logit("User %.100s from %.100s not allowed " + "because a group is listed in DenyGroups", + pw->pw_name, hostname); + return 0; + } + /* + * Return false if AllowGroups isn't empty and one of user's groups + * isn't listed there + */ + if (options.num_allow_groups > 0) + if (!ga_match(options.allow_groups, + options.num_allow_groups)) { + ga_free(); + logit("User %.100s from %.100s not allowed " + "because none of user's groups are listed " + "in AllowGroups", pw->pw_name, hostname); + return 0; + } + ga_free(); + } + +#ifdef CUSTOM_SYS_AUTH_ALLOWED_USER + if (!sys_auth_allowed_user(pw, &loginmsg)) + return 0; +#endif + + /* We found no reason not to let this user try to log on... */ + return 1; +} + +void +auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) +{ + void (*authlog) (const char *fmt,...) = verbose; + char *authmsg; + + if (use_privsep && !mm_is_monitor() && !authctxt->postponed) + return; + + /* Raise logging level */ + if (authenticated == 1 || + !authctxt->valid || + authctxt->failures >= options.max_authtries / 2 || + strcmp(method, "password") == 0) + authlog = logit; + + if (authctxt->postponed) + authmsg = "Postponed"; + else + authmsg = authenticated ? "Accepted" : "Failed"; + + authlog("%s %s for %s%.100s from %.200s port %d%s", + authmsg, + method, + authctxt->valid ? "" : "invalid user ", + authctxt->user, + get_remote_ipaddr(), + get_remote_port(), + info); + +#ifdef CUSTOM_FAILED_LOGIN + if (authenticated == 0 && !authctxt->postponed && + (strcmp(method, "password") == 0 || + strncmp(method, "keyboard-interactive", 20) == 0 || + strcmp(method, "challenge-response") == 0)) + record_failed_login(authctxt->user, + get_canonical_hostname(options.use_dns), "ssh"); +# ifdef WITH_AIXAUTHENTICATE + if (authenticated) + sys_auth_record_login(authctxt->user, + get_canonical_hostname(options.use_dns), "ssh", &loginmsg); +# endif +#endif +#ifdef SSH_AUDIT_EVENTS + if (authenticated == 0 && !authctxt->postponed) + audit_event(audit_classify_auth(method)); +#endif +} + +/* + * Check whether root logins are disallowed. + */ +int +auth_root_allowed(char *method) +{ + switch (options.permit_root_login) { + case PERMIT_YES: + return 1; + case PERMIT_NO_PASSWD: + if (strcmp(method, "password") != 0) + return 1; + break; + case PERMIT_FORCED_ONLY: + if (forced_command) { + logit("Root login accepted for forced command."); + return 1; + } + break; + } + logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); + return 0; +} + + +/* + * Given a template and a passwd structure, build a filename + * by substituting % tokenised options. Currently, %% becomes '%', + * %h becomes the home directory and %u the username. + * + * This returns a buffer allocated by xmalloc. + */ +char * +expand_authorized_keys(const char *filename, struct passwd *pw) +{ + char *file, ret[MAXPATHLEN]; + int i; + + file = percent_expand(filename, "h", pw->pw_dir, + "u", pw->pw_name, (char *)NULL); + + /* + * Ensure that filename starts anchored. If not, be backward + * compatible and prepend the '%h/' + */ + if (*file == '/') + return (file); + + i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); + if (i < 0 || (size_t)i >= sizeof(ret)) + fatal("expand_authorized_keys: path too long"); + xfree(file); + return (xstrdup(ret)); +} + +char * +authorized_principals_file(struct passwd *pw) +{ + if (options.authorized_principals_file == NULL) + return NULL; + return expand_authorized_keys(options.authorized_principals_file, pw); +} + +/* return ok if key exists in sysfile or userfile */ +HostStatus +check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, + const char *sysfile, const char *userfile) +{ + char *user_hostfile; + struct stat st; + HostStatus host_status; + struct hostkeys *hostkeys; + const struct hostkey_entry *found; + + hostkeys = init_hostkeys(); + load_hostkeys(hostkeys, host, sysfile); + if (userfile != NULL) { + user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); + if (options.strict_modes && + (stat(user_hostfile, &st) == 0) && + ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || + (st.st_mode & 022) != 0)) { + logit("Authentication refused for %.100s: " + "bad owner or modes for %.200s", + pw->pw_name, user_hostfile); + auth_debug_add("Ignored %.200s: bad ownership or modes", + user_hostfile); + } else { + temporarily_use_uid(pw); + load_hostkeys(hostkeys, host, user_hostfile); + restore_uid(); + } + xfree(user_hostfile); + } + host_status = check_key_in_hostkeys(hostkeys, key, &found); + if (host_status == HOST_REVOKED) + error("WARNING: revoked key for %s attempted authentication", + found->host); + else if (host_status == HOST_OK) + debug("%s: key for %s found at %s:%ld", __func__, + found->host, found->file, found->line); + else + debug("%s: key for host %s not found", __func__, host); + + free_hostkeys(hostkeys); + + return host_status; +} + + +/* + * Check a given file for security. This is defined as all components + * of the path to the file must be owned by either the owner of + * of the file or root and no directories must be group or world writable. + * + * XXX Should any specific check be done for sym links ? + * + * Takes an open file descriptor, the file name, a uid and and + * error buffer plus max size as arguments. + * + * Returns 0 on success and -1 on failure + */ +static int +secure_filename(FILE *f, const char *file, struct passwd *pw, + char *err, size_t errlen) +{ + uid_t uid = pw->pw_uid; + char buf[MAXPATHLEN], homedir[MAXPATHLEN]; + char *cp; + int comparehome = 0; + struct stat st; + + if (realpath(file, buf) == NULL) { + snprintf(err, errlen, "realpath %s failed: %s", file, + strerror(errno)); + return -1; + } + if (realpath(pw->pw_dir, homedir) != NULL) + comparehome = 1; + + /* check the open file to avoid races */ + if (fstat(fileno(f), &st) < 0 || + (st.st_uid != 0 && st.st_uid != uid) || + (st.st_mode & 022) != 0) { +#ifdef ANDROID + /* needed to allow root login on android */ + if (getuid() != 0) +#endif + { + snprintf(err, errlen, "bad ownership or modes for file %s", + buf); + return -1; + } + } + + /* for each component of the canonical path, walking upwards */ + for (;;) { + if ((cp = dirname(buf)) == NULL) { + snprintf(err, errlen, "dirname() failed"); + return -1; + } + strlcpy(buf, cp, sizeof(buf)); + +#ifndef ANDROID + /* /data is owned by system user, which causes this check to fail */ + if (stat(buf, &st) < 0 || + (st.st_uid != 0 && st.st_uid != uid) || + (st.st_mode & 022) != 0) { + snprintf(err, errlen, + "bad ownership or modes for directory %s", buf); + return -1; + } +#endif + /* If are past the homedir then we can stop */ + if (comparehome && strcmp(homedir, buf) == 0) + break; + + /* + * dirname should always complete with a "/" path, + * but we can be paranoid and check for "." too + */ + if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) + break; + } + return 0; +} + +static FILE * +auth_openfile(const char *file, struct passwd *pw, int strict_modes, + int log_missing, char *file_type) +{ + char line[1024]; + struct stat st; + int fd; + FILE *f; + + if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { + if (log_missing || errno != ENOENT) + debug("Could not open %s '%s': %s", file_type, file, + strerror(errno)); + return NULL; + } + + if (fstat(fd, &st) < 0) { + close(fd); + return NULL; + } + if (!S_ISREG(st.st_mode)) { + logit("User %s %s %s is not a regular file", + pw->pw_name, file_type, file); + close(fd); + return NULL; + } + unset_nonblock(fd); + if ((f = fdopen(fd, "r")) == NULL) { + close(fd); + return NULL; + } + if (strict_modes && + secure_filename(f, file, pw, line, sizeof(line)) != 0) { + fclose(f); + logit("Authentication refused: %s", line); + auth_debug_add("Ignored %s: %s", file_type, line); + return NULL; + } + + return f; +} + + +FILE * +auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) +{ + return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); +} + +FILE * +auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) +{ + return auth_openfile(file, pw, strict_modes, 0, + "authorized principals"); +} + +struct passwd * +getpwnamallow(const char *user) +{ +#ifdef HAVE_LOGIN_CAP + extern login_cap_t *lc; +#ifdef BSD_AUTH + auth_session_t *as; +#endif +#endif + struct passwd *pw; + + parse_server_match_config(&options, user, + get_canonical_hostname(options.use_dns), get_remote_ipaddr()); + +#if defined(_AIX) && defined(HAVE_SETAUTHDB) + aix_setauthdb(user); +#endif + + pw = getpwnam(user); + +#if defined(_AIX) && defined(HAVE_SETAUTHDB) + aix_restoreauthdb(); +#endif +#ifdef HAVE_CYGWIN + /* + * Windows usernames are case-insensitive. To avoid later problems + * when trying to match the username, the user is only allowed to + * login if the username is given in the same case as stored in the + * user database. + */ + if (pw != NULL && strcmp(user, pw->pw_name) != 0) { + logit("Login name %.100s does not match stored username %.100s", + user, pw->pw_name); + pw = NULL; + } +#endif + if (pw == NULL) { + logit("Invalid user %.100s from %.100s", + user, get_remote_ipaddr()); +#ifdef CUSTOM_FAILED_LOGIN + record_failed_login(user, + get_canonical_hostname(options.use_dns), "ssh"); +#endif +#ifdef SSH_AUDIT_EVENTS + audit_event(SSH_INVALID_USER); +#endif /* SSH_AUDIT_EVENTS */ + return (NULL); + } + if (!allowed_user(pw)) + return (NULL); +#ifdef HAVE_LOGIN_CAP + if ((lc = login_getclass(pw->pw_class)) == NULL) { + debug("unable to get login class: %s", user); + return (NULL); + } +#ifdef BSD_AUTH + if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || + auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { + debug("Approval failure for %s", user); + pw = NULL; + } + if (as != NULL) + auth_close(as); +#endif +#endif + if (pw != NULL) + return (pwcopy(pw)); + return (NULL); +} + +/* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ +int +auth_key_is_revoked(Key *key) +{ + char *key_fp; + + if (options.revoked_keys_file == NULL) + return 0; + + switch (key_in_file(key, options.revoked_keys_file, 0)) { + case 0: + /* key not revoked */ + return 0; + case -1: + /* Error opening revoked_keys_file: refuse all keys */ + error("Revoked keys file is unreadable: refusing public key " + "authentication"); + return 1; + case 1: + /* Key revoked */ + key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); + error("WARNING: authentication attempt with a revoked " + "%s key %s ", key_type(key), key_fp); + xfree(key_fp); + return 1; + } + fatal("key_in_file returned junk"); +} + +void +auth_debug_add(const char *fmt,...) +{ + char buf[1024]; + va_list args; + + if (!auth_debug_init) + return; + + va_start(args, fmt); + vsnprintf(buf, sizeof(buf), fmt, args); + va_end(args); + buffer_put_cstring(&auth_debug, buf); +} + +void +auth_debug_send(void) +{ + char *msg; + + if (!auth_debug_init) + return; + while (buffer_len(&auth_debug)) { + msg = buffer_get_string(&auth_debug, NULL); + packet_send_debug("%s", msg); + xfree(msg); + } +} + +void +auth_debug_reset(void) +{ + if (auth_debug_init) + buffer_clear(&auth_debug); + else { + buffer_init(&auth_debug); + auth_debug_init = 1; + } +} + +struct passwd * +fakepw(void) +{ + static struct passwd fake; + + memset(&fake, 0, sizeof(fake)); + fake.pw_name = "NOUSER"; + fake.pw_passwd = + "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; +#ifdef HAVE_PW_GECOS_IN_PASSWD + fake.pw_gecos = "NOUSER"; +#endif + fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid; + fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid; +#ifdef HAVE_PW_CLASS_IN_PASSWD + fake.pw_class = ""; +#endif + fake.pw_dir = "/nonexist"; + fake.pw_shell = "/nonexist"; + + return (&fake); +} |