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openssh-portable/auth2-pubkey.c

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/* $OpenBSD: auth2-pubkey.c,v 1.41 2014/07/15 15:54:14 millert 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/wait.h>
#include <errno.h>
#include <fcntl.h>
#ifdef HAVE_PATHS_H
# include <paths.h>
#endif
#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "packet.h"
#include "buffer.h"
#include "log.h"
#include "misc.h"
#include "servconf.h"
#include "compat.h"
#include "key.h"
#include "hostfile.h"
#include "auth.h"
#include "pathnames.h"
#include "uidswap.h"
#include "auth-options.h"
#include "canohost.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "authfile.h"
#include "match.h"
/* import */
extern ServerOptions options;
extern u_char *session_id2;
extern u_int session_id2_len;
static int
userauth_pubkey(Authctxt *authctxt)
{
Buffer b;
Key *key = NULL;
char *pkalg, *userstyle;
u_char *pkblob, *sig;
u_int alen, blen, slen;
int have_sig, pktype;
int authenticated = 0;
if (!authctxt->valid) {
debug2("userauth_pubkey: disabled because of invalid user");
return 0;
}
have_sig = packet_get_char();
if (datafellows & SSH_BUG_PKAUTH) {
debug2("userauth_pubkey: SSH_BUG_PKAUTH");
/* no explicit pkalg given */
pkblob = packet_get_string(&blen);
buffer_init(&b);
buffer_append(&b, pkblob, blen);
/* so we have to extract the pkalg from the pkblob */
pkalg = buffer_get_string(&b, &alen);
buffer_free(&b);
} else {
pkalg = packet_get_string(&alen);
pkblob = packet_get_string(&blen);
}
pktype = key_type_from_name(pkalg);
if (pktype == KEY_UNSPEC) {
/* this is perfectly legal */
logit("userauth_pubkey: unsupported public key algorithm: %s",
pkalg);
goto done;
}
key = key_from_blob(pkblob, blen);
if (key == NULL) {
error("userauth_pubkey: cannot decode key: %s", pkalg);
goto done;
}
if (key->type != pktype) {
error("userauth_pubkey: type mismatch for decoded key "
"(received %d, expected %d)", key->type, pktype);
goto done;
}
if (key_type_plain(key->type) == KEY_RSA &&
(datafellows & SSH_BUG_RSASIGMD5) != 0) {
logit("Refusing RSA key because client uses unsafe "
"signature scheme");
goto done;
}
if (have_sig) {
sig = packet_get_string(&slen);
packet_check_eom();
buffer_init(&b);
if (datafellows & SSH_OLD_SESSIONID) {
buffer_append(&b, session_id2, session_id2_len);
} else {
buffer_put_string(&b, session_id2, session_id2_len);
}
/* reconstruct packet */
buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
xasprintf(&userstyle, "%s%s%s", authctxt->user,
authctxt->style ? ":" : "",
authctxt->style ? authctxt->style : "");
buffer_put_cstring(&b, userstyle);
free(userstyle);
buffer_put_cstring(&b,
datafellows & SSH_BUG_PKSERVICE ?
"ssh-userauth" :
authctxt->service);
if (datafellows & SSH_BUG_PKAUTH) {
buffer_put_char(&b, have_sig);
} else {
buffer_put_cstring(&b, "publickey");
buffer_put_char(&b, have_sig);
buffer_put_cstring(&b, pkalg);
}
buffer_put_string(&b, pkblob, blen);
#ifdef DEBUG_PK
buffer_dump(&b);
#endif
pubkey_auth_info(authctxt, key, NULL);
/* test for correct signature */
authenticated = 0;
if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
buffer_len(&b))) == 1)
authenticated = 1;
buffer_free(&b);
free(sig);
} else {
debug("test whether pkalg/pkblob are acceptable");
packet_check_eom();
/* XXX fake reply and always send PK_OK ? */
/*
* XXX this allows testing whether a user is allowed
* to login: if you happen to have a valid pubkey this
* message is sent. the message is NEVER sent at all
* if a user is not allowed to login. is this an
* issue? -markus
*/
if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
packet_start(SSH2_MSG_USERAUTH_PK_OK);
packet_put_string(pkalg, alen);
packet_put_string(pkblob, blen);
packet_send();
packet_write_wait();
authctxt->postponed = 1;
}
}
if (authenticated != 1)
auth_clear_options();
done:
debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
if (key != NULL)
key_free(key);
free(pkalg);
free(pkblob);
return authenticated;
}
void
pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...)
{
char *fp, *extra;
va_list ap;
int i;
extra = NULL;
if (fmt != NULL) {
va_start(ap, fmt);
i = vasprintf(&extra, fmt, ap);
va_end(ap);
if (i < 0 || extra == NULL)
fatal("%s: vasprintf failed", __func__);
}
if (key_is_cert(key)) {
fp = key_fingerprint(key->cert->signature_key,
SSH_FP_MD5, SSH_FP_HEX);
auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s",
key_type(key), key->cert->key_id,
(unsigned long long)key->cert->serial,
key_type(key->cert->signature_key), fp,
extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
free(fp);
} else {
fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
auth_info(authctxt, "%s %s%s%s", key_type(key), fp,
extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
free(fp);
}
free(extra);
}
static int
match_principals_option(const char *principal_list, struct sshkey_cert *cert)
{
char *result;
u_int i;
/* XXX percent_expand() sequences for authorized_principals? */
for (i = 0; i < cert->nprincipals; i++) {
if ((result = match_list(cert->principals[i],
principal_list, NULL)) != NULL) {
debug3("matched principal from key options \"%.100s\"",
result);
free(result);
return 1;
}
}
return 0;
}
static int
match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
{
FILE *f;
char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
u_long linenum = 0;
u_int i;
temporarily_use_uid(pw);
debug("trying authorized principals file %s", file);
if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
restore_uid();
return 0;
}
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
/* Skip leading whitespace. */
for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
;
/* Skip blank and comment lines. */
if ((ep = strchr(cp, '#')) != NULL)
*ep = '\0';
if (!*cp || *cp == '\n')
continue;
/* Trim trailing whitespace. */
ep = cp + strlen(cp) - 1;
while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
*ep-- = '\0';
/*
* If the line has internal whitespace then assume it has
* key options.
*/
line_opts = NULL;
if ((ep = strrchr(cp, ' ')) != NULL ||
(ep = strrchr(cp, '\t')) != NULL) {
for (; *ep == ' ' || *ep == '\t'; ep++)
;
line_opts = cp;
cp = ep;
}
for (i = 0; i < cert->nprincipals; i++) {
if (strcmp(cp, cert->principals[i]) == 0) {
debug3("matched principal \"%.100s\" "
"from file \"%s\" on line %lu",
cert->principals[i], file, linenum);
if (auth_parse_options(pw, line_opts,
file, linenum) != 1)
continue;
fclose(f);
restore_uid();
return 1;
}
}
}
fclose(f);
restore_uid();
return 0;
}
/*
* Checks whether key is allowed in authorized_keys-format file,
* returns 1 if the key is allowed or 0 otherwise.
*/
static int
check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
{
char line[SSH_MAX_PUBKEY_BYTES];
const char *reason;
int found_key = 0;
u_long linenum = 0;
Key *found;
char *fp;
found_key = 0;
found = NULL;
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
char *cp, *key_options = NULL;
if (found != NULL)
key_free(found);
found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
auth_clear_options();
/* Skip leading whitespace, empty and comment lines. */
for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
;
if (!*cp || *cp == '\n' || *cp == '#')
continue;
if (key_read(found, &cp) != 1) {
/* no key? check if there are options for this key */
int quoted = 0;
debug2("user_key_allowed: check options: '%s'", cp);
key_options = cp;
for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
if (*cp == '\\' && cp[1] == '"')
cp++; /* Skip both */
else if (*cp == '"')
quoted = !quoted;
}
/* Skip remaining whitespace. */
for (; *cp == ' ' || *cp == '\t'; cp++)
;
if (key_read(found, &cp) != 1) {
debug2("user_key_allowed: advance: '%s'", cp);
/* still no key? advance to next line*/
continue;
}
}
if (key_is_cert(key)) {
if (!key_equal(found, key->cert->signature_key))
continue;
if (auth_parse_options(pw, key_options, file,
linenum) != 1)
continue;
if (!key_is_cert_authority)
continue;
fp = key_fingerprint(found, SSH_FP_MD5,
SSH_FP_HEX);
debug("matching CA found: file %s, line %lu, %s %s",
file, linenum, key_type(found), fp);
/*
* If the user has specified a list of principals as
* a key option, then prefer that list to matching
* their username in the certificate principals list.
*/
if (authorized_principals != NULL &&
!match_principals_option(authorized_principals,
key->cert)) {
reason = "Certificate does not contain an "
"authorized principal";
fail_reason:
free(fp);
error("%s", reason);
auth_debug_add("%s", reason);
continue;
}
if (key_cert_check_authority(key, 0, 0,
authorized_principals == NULL ? pw->pw_name : NULL,
&reason) != 0)
goto fail_reason;
if (auth_cert_options(key, pw) != 0) {
free(fp);
continue;
}
verbose("Accepted certificate ID \"%s\" "
"signed by %s CA %s via %s", key->cert->key_id,
key_type(found), fp, file);
free(fp);
found_key = 1;
break;
} else if (key_equal(found, key)) {
if (auth_parse_options(pw, key_options, file,
linenum) != 1)
continue;
if (key_is_cert_authority)
continue;
found_key = 1;
fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
debug("matching key found: file %s, line %lu %s %s",
file, linenum, key_type(found), fp);
free(fp);
break;
}
}
if (found != NULL)
key_free(found);
if (!found_key)
debug2("key not found");
return found_key;
}
/* Authenticate a certificate key against TrustedUserCAKeys */
static int
user_cert_trusted_ca(struct passwd *pw, Key *key)
{
char *ca_fp, *principals_file = NULL;
const char *reason;
int ret = 0;
if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
return 0;
ca_fp = key_fingerprint(key->cert->signature_key,
SSH_FP_MD5, SSH_FP_HEX);
if (key_in_file(key->cert->signature_key,
options.trusted_user_ca_keys, 1) != 1) {
debug2("%s: CA %s %s is not listed in %s", __func__,
key_type(key->cert->signature_key), ca_fp,
options.trusted_user_ca_keys);
goto out;
}
/*
* If AuthorizedPrincipals is in use, then compare the certificate
* principals against the names in that file rather than matching
* against the username.
*/
if ((principals_file = authorized_principals_file(pw)) != NULL) {
if (!match_principals_file(principals_file, pw, key->cert)) {
reason = "Certificate does not contain an "
"authorized principal";
fail_reason:
error("%s", reason);
auth_debug_add("%s", reason);
goto out;
}
}
if (key_cert_check_authority(key, 0, 1,
principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
goto fail_reason;
if (auth_cert_options(key, pw) != 0)
goto out;
verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
options.trusted_user_ca_keys);
ret = 1;
out:
free(principals_file);
free(ca_fp);
return ret;
}
/*
* Checks whether key is allowed in file.
* returns 1 if the key is allowed or 0 otherwise.
*/
static int
user_key_allowed2(struct passwd *pw, Key *key, char *file)
{
FILE *f;
int found_key = 0;
/* Temporarily use the user's uid. */
temporarily_use_uid(pw);
debug("trying public key file %s", file);
if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
found_key = check_authkeys_file(f, file, key, pw);
fclose(f);
}
restore_uid();
return found_key;
}
/*
* Checks whether key is allowed in output of command.
* returns 1 if the key is allowed or 0 otherwise.
*/
static int
user_key_command_allowed2(struct passwd *user_pw, Key *key)
{
FILE *f;
int ok, found_key = 0;
struct passwd *pw;
struct stat st;
int status, devnull, p[2], i;
pid_t pid;
char *username, errmsg[512];
if (options.authorized_keys_command == NULL ||
options.authorized_keys_command[0] != '/')
return 0;
if (options.authorized_keys_command_user == NULL) {
error("No user for AuthorizedKeysCommand specified, skipping");
return 0;
}
username = percent_expand(options.authorized_keys_command_user,
"u", user_pw->pw_name, (char *)NULL);
pw = getpwnam(username);
if (pw == NULL) {
error("AuthorizedKeysCommandUser \"%s\" not found: %s",
username, strerror(errno));
free(username);
return 0;
}
free(username);
temporarily_use_uid(pw);
if (stat(options.authorized_keys_command, &st) < 0) {
error("Could not stat AuthorizedKeysCommand \"%s\": %s",
options.authorized_keys_command, strerror(errno));
goto out;
}
if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
errmsg, sizeof(errmsg)) != 0) {
error("Unsafe AuthorizedKeysCommand: %s", errmsg);
goto out;
}
if (pipe(p) != 0) {
error("%s: pipe: %s", __func__, strerror(errno));
goto out;
}
debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"",
options.authorized_keys_command, user_pw->pw_name, pw->pw_name);
/*
* Don't want to call this in the child, where it can fatal() and
* run cleanup_exit() code.
*/
restore_uid();
switch ((pid = fork())) {
case -1: /* error */
error("%s: fork: %s", __func__, strerror(errno));
close(p[0]);
close(p[1]);
return 0;
case 0: /* child */
for (i = 0; i < NSIG; i++)
signal(i, SIG_DFL);
if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
error("%s: open %s: %s", __func__, _PATH_DEVNULL,
strerror(errno));
_exit(1);
}
/* Keep stderr around a while longer to catch errors */
if (dup2(devnull, STDIN_FILENO) == -1 ||
dup2(p[1], STDOUT_FILENO) == -1) {
error("%s: dup2: %s", __func__, 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("setresgid %u: %s", (u_int)pw->pw_gid,
strerror(errno));
_exit(1);
}
if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
error("setresuid %u: %s", (u_int)pw->pw_uid,
strerror(errno));
_exit(1);
}
/* stdin is pointed to /dev/null at this point */
if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
error("%s: dup2: %s", __func__, strerror(errno));
_exit(1);
}
execl(options.authorized_keys_command,
options.authorized_keys_command, user_pw->pw_name, NULL);
error("AuthorizedKeysCommand %s exec failed: %s",
options.authorized_keys_command, strerror(errno));
_exit(127);
default: /* parent */
break;
}
temporarily_use_uid(pw);
close(p[1]);
if ((f = fdopen(p[0], "r")) == NULL) {
error("%s: fdopen: %s", __func__, strerror(errno));
close(p[0]);
/* Don't leave zombie child */
kill(pid, SIGTERM);
while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
;
goto out;
}
ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
fclose(f);
while (waitpid(pid, &status, 0) == -1) {
if (errno != EINTR) {
error("%s: waitpid: %s", __func__, strerror(errno));
goto out;
}
}
if (WIFSIGNALED(status)) {
error("AuthorizedKeysCommand %s exited on signal %d",
options.authorized_keys_command, WTERMSIG(status));
goto out;
} else if (WEXITSTATUS(status) != 0) {
error("AuthorizedKeysCommand %s returned status %d",
options.authorized_keys_command, WEXITSTATUS(status));
goto out;
}
found_key = ok;
out:
restore_uid();
return found_key;
}
/*
* Check whether key authenticates and authorises the user.
*/
int
user_key_allowed(struct passwd *pw, Key *key)
{
u_int success, i;
char *file;
if (auth_key_is_revoked(key))
return 0;
if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
return 0;
success = user_cert_trusted_ca(pw, key);
if (success)
return success;
success = user_key_command_allowed2(pw, key);
if (success > 0)
return success;
for (i = 0; !success && i < options.num_authkeys_files; i++) {
if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
continue;
file = expand_authorized_keys(
options.authorized_keys_files[i], pw);
success = user_key_allowed2(pw, key, file);
free(file);
}
return success;
}
Authmethod method_pubkey = {
"publickey",
userauth_pubkey,
&options.pubkey_authentication
};
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