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auth.c
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auth.c
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/* $OpenBSD: auth.c,v 1.132 2018/07/11 08:19:35 martijn 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/socket.h>
#include <sys/wait.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
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include <netdb.h>
#include "xmalloc.h"
#include "match.h"
#include "groupaccess.h"
#include "log.h"
#include "sshbuf.h"
#include "misc.h"
#include "servconf.h"
#include "sshkey.h"
#include "hostfile.h"
#include "auth.h"
#include "auth-options.h"
#include "canohost.h"
#include "uidswap.h"
#include "packet.h"
#include "loginrec.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "authfile.h"
#include "monitor_wrap.h"
#include "authfile.h"
#include "ssherr.h"
#include "compat.h"
#include "channels.h"
/* import */
extern ServerOptions options;
extern int use_privsep;
extern struct sshbuf *loginmsg;
extern struct passwd *privsep_pw;
extern struct sshauthopt *auth_opts;
/* Debugging messages */
static struct sshbuf *auth_debug;
/*
* 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 ssh *ssh = active_state; /* XXX */
struct stat st;
const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
u_int i;
int r;
#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);
free(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);
free(shell);
return 0;
}
free(shell);
}
if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
options.num_deny_groups > 0 || options.num_allow_groups > 0) {
hostname = auth_get_canonical_hostname(ssh, options.use_dns);
ipaddr = ssh_remote_ipaddr(ssh);
}
/* Return false if user is listed in DenyUsers */
if (options.num_deny_users > 0) {
for (i = 0; i < options.num_deny_users; i++) {
r = match_user(pw->pw_name, hostname, ipaddr,
options.deny_users[i]);
if (r < 0) {
fatal("Invalid DenyUsers pattern \"%.100s\"",
options.deny_users[i]);
} else if (r != 0) {
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++) {
r = match_user(pw->pw_name, hostname, ipaddr,
options.allow_users[i]);
if (r < 0) {
fatal("Invalid AllowUsers pattern \"%.100s\"",
options.allow_users[i]);
} else if (r == 1)
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;
}
/*
* Formats any key left in authctxt->auth_method_key for inclusion in
* auth_log()'s message. Also includes authxtct->auth_method_info if present.
*/
static char *
format_method_key(Authctxt *authctxt)
{
const struct sshkey *key = authctxt->auth_method_key;
const char *methinfo = authctxt->auth_method_info;
char *fp, *ret = NULL;
if (key == NULL)
return NULL;
if (sshkey_is_cert(key)) {
fp = sshkey_fingerprint(key->cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
xasprintf(&ret, "%s ID %s (serial %llu) CA %s %s%s%s",
sshkey_type(key), key->cert->key_id,
(unsigned long long)key->cert->serial,
sshkey_type(key->cert->signature_key),
fp == NULL ? "(null)" : fp,
methinfo == NULL ? "" : ", ",
methinfo == NULL ? "" : methinfo);
free(fp);
} else {
fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT);
xasprintf(&ret, "%s %s%s%s", sshkey_type(key),
fp == NULL ? "(null)" : fp,
methinfo == NULL ? "" : ", ",
methinfo == NULL ? "" : methinfo);
free(fp);
}
return ret;
}
void
auth_log(Authctxt *authctxt, int authenticated, int partial,
const char *method, const char *submethod)
{
struct ssh *ssh = active_state; /* XXX */
void (*authlog) (const char *fmt,...) = verbose;
const char *authmsg;
char *extra = NULL;
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 if (partial)
authmsg = "Partial";
else
authmsg = authenticated ? "Accepted" : "Failed";
if ((extra = format_method_key(authctxt)) == NULL) {
if (authctxt->auth_method_info != NULL)
extra = xstrdup(authctxt->auth_method_info);
}
authlog("%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s",
authmsg,
method,
submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod,
authctxt->valid ? "" : "invalid user ",
authctxt->user,
ssh_remote_ipaddr(ssh),
ssh_remote_port(ssh),
extra != NULL ? ": " : "",
extra != NULL ? extra : "");
free(extra);
#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,
auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
# ifdef WITH_AIXAUTHENTICATE
if (authenticated)
sys_auth_record_login(authctxt->user,
auth_get_canonical_hostname(ssh, options.use_dns), "ssh",
&loginmsg);
# endif
#endif
#ifdef SSH_AUDIT_EVENTS
if (authenticated == 0 && !authctxt->postponed)
audit_event(audit_classify_auth(method));
#endif
}
void
auth_maxtries_exceeded(Authctxt *authctxt)
{
struct ssh *ssh = active_state; /* XXX */
error("maximum authentication attempts exceeded for "
"%s%.100s from %.200s port %d ssh2",
authctxt->valid ? "" : "invalid user ",
authctxt->user,
ssh_remote_ipaddr(ssh),
ssh_remote_port(ssh));
packet_disconnect("Too many authentication failures");
/* NOTREACHED */
}
/*
* Check whether root logins are disallowed.
*/
int
auth_root_allowed(struct ssh *ssh, const char *method)
{
switch (options.permit_root_login) {
case PERMIT_YES:
return 1;
case PERMIT_NO_PASSWD:
if (strcmp(method, "publickey") == 0 ||
strcmp(method, "hostbased") == 0 ||
strcmp(method, "gssapi-with-mic") == 0)
return 1;
break;
case PERMIT_FORCED_ONLY:
if (auth_opts->force_command != NULL) {
logit("Root login accepted for forced command.");
return 1;
}
break;
}
logit("ROOT LOGIN REFUSED FROM %.200s port %d",
ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
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, uidstr[32], ret[PATH_MAX];
int i;
snprintf(uidstr, sizeof(uidstr), "%llu",
(unsigned long long)pw->pw_uid);
file = percent_expand(filename, "h", pw->pw_dir,
"u", pw->pw_name, "U", uidstr, (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");
free(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, struct sshkey *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();
}
free(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;
}
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 &&
safe_path_fd(fileno(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)
{
struct ssh *ssh = active_state; /* XXX */
#ifdef HAVE_LOGIN_CAP
extern login_cap_t *lc;
#ifdef BSD_AUTH
auth_session_t *as;
#endif
#endif
struct passwd *pw;
struct connection_info *ci = get_connection_info(1, options.use_dns);
ci->user = user;
parse_server_match_config(&options, ci);
log_change_level(options.log_level);
process_permitopen(ssh, &options);
#if defined(_AIX) && defined(HAVE_SETAUTHDB)
aix_setauthdb(user);
#endif
#if defined(ANDROID)
// Android has a fixed set of users. Any incoming user that we can't
// identify should be authenticated as the shell user.
if (strcmp(user, "root") && strcmp(user, "shell")) {
logit("Login name %.100s forced to shell", user);
user = "shell";
}
#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 port %d",
user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
#ifdef CUSTOM_FAILED_LOGIN
record_failed_login(user,
auth_get_canonical_hostname(ssh, 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(struct sshkey *key)
{
char *fp = NULL;
int r;
if (options.revoked_keys_file == NULL)
return 0;
if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT)) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
error("%s: fingerprint key: %s", __func__, ssh_err(r));
goto out;
}
r = sshkey_check_revoked(key, options.revoked_keys_file);
switch (r) {
case 0:
break; /* not revoked */
case SSH_ERR_KEY_REVOKED:
error("Authentication key %s %s revoked by file %s",
sshkey_type(key), fp, options.revoked_keys_file);
goto out;
default:
error("Error checking authentication key %s %s in "
"revoked keys file %s: %s", sshkey_type(key), fp,
options.revoked_keys_file, ssh_err(r));
goto out;
}
/* Success */
r = 0;
out:
free(fp);
return r == 0 ? 0 : 1;
}
void
auth_debug_add(const char *fmt,...)
{
char buf[1024];
va_list args;
int r;
if (auth_debug == NULL)
return;
va_start(args, fmt);
vsnprintf(buf, sizeof(buf), fmt, args);
va_end(args);
if ((r = sshbuf_put_cstring(auth_debug, buf)) != 0)
fatal("%s: sshbuf_put_cstring: %s", __func__, ssh_err(r));
}
void
auth_debug_send(void)
{
struct ssh *ssh = active_state; /* XXX */
char *msg;
int r;
if (auth_debug == NULL)
return;
while (sshbuf_len(auth_debug) != 0) {
if ((r = sshbuf_get_cstring(auth_debug, &msg, NULL)) != 0)
fatal("%s: sshbuf_get_cstring: %s",
__func__, ssh_err(r));
ssh_packet_send_debug(ssh, "%s", msg);
free(msg);
}
}
void
auth_debug_reset(void)
{
if (auth_debug != NULL)
sshbuf_reset(auth_debug);
else if ((auth_debug = sshbuf_new()) == NULL)
fatal("%s: sshbuf_new failed", __func__);
}
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_STRUCT_PASSWD_PW_GECOS
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_STRUCT_PASSWD_PW_CLASS
fake.pw_class = "";
#endif
fake.pw_dir = "/nonexist";
fake.pw_shell = "/nonexist";
return (&fake);
}
/*
* Returns the remote DNS hostname as a string. The returned string must not
* be freed. NB. this will usually trigger a DNS query the first time it is
* called.
* This function does additional checks on the hostname to mitigate some
* attacks on legacy rhosts-style authentication.
* XXX is RhostsRSAAuthentication vulnerable to these?
* XXX Can we remove these checks? (or if not, remove RhostsRSAAuthentication?)
*/
static char *
remote_hostname(struct ssh *ssh)
{
struct sockaddr_storage from;
socklen_t fromlen;
struct addrinfo hints, *ai, *aitop;
char name[NI_MAXHOST], ntop2[NI_MAXHOST];
const char *ntop = ssh_remote_ipaddr(ssh);
/* Get IP address of client. */
fromlen = sizeof(from);
memset(&from, 0, sizeof(from));
if (getpeername(ssh_packet_get_connection_in(ssh),
(struct sockaddr *)&from, &fromlen) < 0) {
debug("getpeername failed: %.100s", strerror(errno));
return strdup(ntop);
}
ipv64_normalise_mapped(&from, &fromlen);
if (from.ss_family == AF_INET6)
fromlen = sizeof(struct sockaddr_in6);
debug3("Trying to reverse map address %.100s.", ntop);
/* Map the IP address to a host name. */
if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
NULL, 0, NI_NAMEREQD) != 0) {
/* Host name not found. Use ip address. */
return strdup(ntop);
}
/*
* if reverse lookup result looks like a numeric hostname,
* someone is trying to trick us by PTR record like following:
* 1.1.1.10.in-addr.arpa. IN PTR 2.3.4.5
*/
memset(&hints, 0, sizeof(hints));
hints.ai_socktype = SOCK_DGRAM; /*dummy*/
hints.ai_flags = AI_NUMERICHOST;
if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
name, ntop);
freeaddrinfo(ai);
return strdup(ntop);
}
/* Names are stored in lowercase. */
lowercase(name);
/*
* Map it back to an IP address and check that the given
* address actually is an address of this host. This is
* necessary because anyone with access to a name server can
* define arbitrary names for an IP address. Mapping from
* name to IP address can be trusted better (but can still be
* fooled if the intruder has access to the name server of
* the domain).
*/
memset(&hints, 0, sizeof(hints));
hints.ai_family = from.ss_family;
hints.ai_socktype = SOCK_STREAM;
if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
logit("reverse mapping checking getaddrinfo for %.700s "
"[%s] failed.", name, ntop);
return strdup(ntop);
}
/* Look for the address from the list of addresses. */
for (ai = aitop; ai; ai = ai->ai_next) {
if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
(strcmp(ntop, ntop2) == 0))
break;
}
freeaddrinfo(aitop);
/* If we reached the end of the list, the address was not there. */
if (ai == NULL) {
/* Address not found for the host name. */
logit("Address %.100s maps to %.600s, but this does not "
"map back to the address.", ntop, name);
return strdup(ntop);
}
return strdup(name);
}
/*
* Return the canonical name of the host in the other side of the current
* connection. The host name is cached, so it is efficient to call this
* several times.
*/
const char *
auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
{
static char *dnsname;
if (!use_dns)
return ssh_remote_ipaddr(ssh);
else if (dnsname != NULL)
return dnsname;
else {
dnsname = remote_hostname(ssh);
return dnsname;
}
}
/*
* Runs command in a subprocess with a minimal environment.
* Returns pid on success, 0 on failure.
* The child stdout and stderr maybe captured, left attached or sent to
* /dev/null depending on the contents of flags.
* "tag" is prepended to log messages.
* NB. "command" is only used for logging; the actual command executed is
* av[0].
*/
pid_t
subprocess(const char *tag, struct passwd *pw, const char *command,
int ac, char **av, FILE **child, u_int flags)
{
FILE *f = NULL;
struct stat st;
int fd, devnull, p[2], i;
pid_t pid;
char *cp, errmsg[512];
u_int envsize;
char **child_env;
if (child != NULL)
*child = NULL;
debug3("%s: %s command \"%s\" running as %s (flags 0x%x)", __func__,
tag, command, pw->pw_name, flags);
/* Check consistency */
if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
(flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) {
error("%s: inconsistent flags", __func__);
return 0;
}
if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) {
error("%s: inconsistent flags/output", __func__);
return 0;
}
/*
* If executing an explicit binary, then verify the it exists
* and appears safe-ish to execute
*/
if (*av[0] != '/') {
error("%s path is not absolute", tag);
return 0;
}
temporarily_use_uid(pw);
if (stat(av[0], &st) < 0) {
error("Could not stat %s \"%s\": %s", tag,
av[0], strerror(errno));
restore_uid();
return 0;
}
if (safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) {
error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
restore_uid();
return 0;
}
/* Prepare to keep the child's stdout if requested */
if (pipe(p) != 0) {
error("%s: pipe: %s", tag, strerror(errno));
restore_uid();
return 0;
}
restore_uid();
switch ((pid = fork())) {
case -1: /* error */
error("%s: fork: %s", tag, strerror(errno));
close(p[0]);
close(p[1]);
return 0;
case 0: /* child */
/* Prepare a minimal environment for the child. */
envsize = 5;
child_env = xcalloc(sizeof(*child_env), envsize);
child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
child_set_env(&child_env, &envsize, "USER", pw->pw_name);
child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
if ((cp = getenv("LANG")) != NULL)
child_set_env(&child_env, &envsize, "LANG", cp);
for (i = 0; i < NSIG; i++)
signal(i, SIG_DFL);
if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
error("%s: open %s: %s", tag, _PATH_DEVNULL,
strerror(errno));
_exit(1);
}
if (dup2(devnull, STDIN_FILENO) == -1) {
error("%s: dup2: %s", tag, strerror(errno));
_exit(1);
}
/* Set up stdout as requested; leave stderr in place for now. */
fd = -1;
if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0)
fd = p[1];
else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0)
fd = devnull;
if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) {
error("%s: dup2: %s", tag, strerror(errno));
_exit(1);
}
closefrom(STDERR_FILENO + 1);
/* Don't use permanently_set_uid() here to avoid fatal() */
if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
strerror(errno));
_exit(1);
}
if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
strerror(errno));
_exit(1);
}
/* stdin is pointed to /dev/null at this point */
if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 &&
dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
error("%s: dup2: %s", tag, strerror(errno));
_exit(1);
}
execve(av[0], av, child_env);
error("%s exec \"%s\": %s", tag, command, strerror(errno));
_exit(127);
default: /* parent */
break;
}
close(p[1]);
if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0)
close(p[0]);
else if ((f = fdopen(p[0], "r")) == NULL) {
error("%s: fdopen: %s", tag, strerror(errno));
close(p[0]);
/* Don't leave zombie child */
kill(pid, SIGTERM);
while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
;