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openssh-portable/auth2-pubkey.c

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/* $OpenBSD: auth2-pubkey.c,v 1.103 2020/12/22 00:12:22 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 <stdlib.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 <limits.h>
#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "packet.h"
#include "sshbuf.h"
#include "log.h"
#include "misc.h"
#include "servconf.h"
#include "compat.h"
#include "sshkey.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"
#include "ssherr.h"
#include "channels.h" /* XXX for session.h */
#include "session.h" /* XXX for child_set_env(); refactor? */
#include "sk-api.h"
/* import */
extern ServerOptions options;
extern u_char *session_id2;
extern u_int session_id2_len;
static char *
format_key(const struct sshkey *key)
{
char *ret, *fp = sshkey_fingerprint(key,
options.fingerprint_hash, SSH_FP_DEFAULT);
xasprintf(&ret, "%s %s", sshkey_type(key), fp);
free(fp);
return ret;
}
static int
userauth_pubkey(struct ssh *ssh)
{
Authctxt *authctxt = ssh->authctxt;
struct passwd *pw = authctxt->pw;
struct sshbuf *b = NULL;
struct sshkey *key = NULL;
char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
u_char *pkblob = NULL, *sig = NULL, have_sig;
size_t blen, slen;
int r, pktype;
int req_presence = 0, req_verify = 0, authenticated = 0;
struct sshauthopt *authopts = NULL;
struct sshkey_sig_details *sig_details = NULL;
if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
(r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
(r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
fatal_fr(r, "parse packet");
if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) {
char *keystring;
struct sshbuf *pkbuf;
if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL)
fatal_f("sshbuf_from failed");
if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL)
fatal_f("sshbuf_dtob64 failed");
debug2_f("%s user %s %s public key %s %s",
authctxt->valid ? "valid" : "invalid", authctxt->user,
have_sig ? "attempting" : "querying", pkalg, keystring);
sshbuf_free(pkbuf);
free(keystring);
}
pktype = sshkey_type_from_name(pkalg);
if (pktype == KEY_UNSPEC) {
/* this is perfectly legal */
verbose_f("unsupported public key algorithm: %s", pkalg);
goto done;
}
if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
error_fr(r, "parse key");
goto done;
}
if (key == NULL) {
error_f("cannot decode key: %s", pkalg);
goto done;
}
if (key->type != pktype) {
error_f("type mismatch for decoded key "
"(received %d, expected %d)", key->type, pktype);
goto done;
}
if (sshkey_type_plain(key->type) == KEY_RSA &&
(ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
logit("Refusing RSA key because client uses unsafe "
"signature scheme");
goto done;
}
if (auth2_key_already_used(authctxt, key)) {
logit("refusing previously-used %s key", sshkey_type(key));
goto done;
}
if (match_pattern_list(pkalg, options.pubkey_key_types, 0) != 1) {
logit_f("key type %s not in PubkeyAcceptedKeyTypes",
sshkey_ssh_name(key));
goto done;
}
if ((r = sshkey_check_cert_sigtype(key,
options.ca_sign_algorithms)) != 0) {
logit_fr(r, "certificate signature algorithm %s",
(key->cert == NULL || key->cert->signature_type == NULL) ?
"(null)" : key->cert->signature_type);
goto done;
}
key_s = format_key(key);
if (sshkey_is_cert(key))
ca_s = format_key(key->cert->signature_key);
if (have_sig) {
debug3_f("have %s signature for %s%s%s", pkalg, key_s,
ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal_fr(r, "parse signature packet");
if ((b = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if (ssh->compat & SSH_OLD_SESSIONID) {
if ((r = sshbuf_put(b, session_id2, session_id2_len)) != 0)
fatal_fr(r, "put old session id");
} else {
if ((r = sshbuf_put_string(b, session_id2,
session_id2_len)) != 0)
fatal_fr(r, "put session id");
}
if (!authctxt->valid || authctxt->user == NULL) {
debug2_f("disabled because of invalid user");
goto done;
}
/* reconstruct packet */
xasprintf(&userstyle, "%s%s%s", authctxt->user,
authctxt->style ? ":" : "",
authctxt->style ? authctxt->style : "");
if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
(r = sshbuf_put_cstring(b, userstyle)) != 0 ||
(r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
(r = sshbuf_put_cstring(b, "publickey")) != 0 ||
(r = sshbuf_put_u8(b, have_sig)) != 0 ||
(r = sshbuf_put_cstring(b, pkalg)) != 0 ||
(r = sshbuf_put_string(b, pkblob, blen)) != 0)
fatal_fr(r, "reconstruct packet");
#ifdef DEBUG_PK
sshbuf_dump(b, stderr);
#endif
/* test for correct signature */
authenticated = 0;
if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) &&
PRIVSEP(sshkey_verify(key, sig, slen,
sshbuf_ptr(b), sshbuf_len(b),
(ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL,
ssh->compat, &sig_details)) == 0) {
authenticated = 1;
}
if (authenticated == 1 && sig_details != NULL) {
auth2_record_info(authctxt, "signature count = %u",
sig_details->sk_counter);
debug_f("sk_counter = %u, sk_flags = 0x%02x",
sig_details->sk_counter, sig_details->sk_flags);
req_presence = (options.pubkey_auth_options &
PUBKEYAUTH_TOUCH_REQUIRED) ||
!authopts->no_require_user_presence;
if (req_presence && (sig_details->sk_flags &
SSH_SK_USER_PRESENCE_REQD) == 0) {
error("public key %s signature for %s%s from "
"%.128s port %d rejected: user presence "
"(authenticator touch) requirement "
"not met ", key_s,
authctxt->valid ? "" : "invalid user ",
authctxt->user, ssh_remote_ipaddr(ssh),
ssh_remote_port(ssh));
authenticated = 0;
goto done;
}
req_verify = (options.pubkey_auth_options &
PUBKEYAUTH_VERIFY_REQUIRED) ||
authopts->require_verify;
if (req_verify && (sig_details->sk_flags &
SSH_SK_USER_VERIFICATION_REQD) == 0) {
error("public key %s signature for %s%s from "
"%.128s port %d rejected: user "
"verification requirement not met ", key_s,
authctxt->valid ? "" : "invalid user ",
authctxt->user, ssh_remote_ipaddr(ssh),
ssh_remote_port(ssh));
authenticated = 0;
goto done;
}
}
auth2_record_key(authctxt, authenticated, key);
} else {
debug_f("test pkalg %s pkblob %s%s%s", pkalg, key_s,
ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
if ((r = sshpkt_get_end(ssh)) != 0)
fatal_fr(r, "parse packet");
if (!authctxt->valid || authctxt->user == NULL) {
debug2_f("disabled because of invalid user");
goto done;
}
/* 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(ssh, pw, key, 0, NULL))) {
if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK))
!= 0 ||
(r = sshpkt_put_cstring(ssh, pkalg)) != 0 ||
(r = sshpkt_put_string(ssh, pkblob, blen)) != 0 ||
(r = sshpkt_send(ssh)) != 0 ||
(r = ssh_packet_write_wait(ssh)) != 0)
fatal_fr(r, "send packet");
authctxt->postponed = 1;
}
}
done:
if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) {
debug_f("key options inconsistent with existing");
authenticated = 0;
}
debug2_f("authenticated %d pkalg %s", authenticated, pkalg);
sshbuf_free(b);
sshauthopt_free(authopts);
sshkey_free(key);
free(userstyle);
free(pkalg);
free(pkblob);
free(key_s);
free(ca_s);
free(sig);
sshkey_sig_details_free(sig_details);
return authenticated;
}
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;
}
/*
* Process a single authorized_principals format line. Returns 0 and sets
* authoptsp is principal is authorised, -1 otherwise. "loc" is used as a
* log preamble for file/line information.
*/
static int
check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert,
const char *loc, struct sshauthopt **authoptsp)
{
u_int i, found = 0;
char *ep, *line_opts;
const char *reason = NULL;
struct sshauthopt *opts = NULL;
if (authoptsp != NULL)
*authoptsp = NULL;
/* 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;
}
if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) {
debug("%s: bad principals options: %s", loc, reason);
auth_debug_add("%s: bad principals options: %s", loc, reason);
return -1;
}
/* Check principals in cert against those on line */
for (i = 0; i < cert->nprincipals; i++) {
if (strcmp(cp, cert->principals[i]) != 0)
continue;
debug3("%s: matched principal \"%.100s\"",
loc, cert->principals[i]);
found = 1;
}
if (found && authoptsp != NULL) {
*authoptsp = opts;
opts = NULL;
}
sshauthopt_free(opts);
return found ? 0 : -1;
}
static int
process_principals(struct ssh *ssh, FILE *f, const char *file,
const struct sshkey_cert *cert, struct sshauthopt **authoptsp)
{
char loc[256], *line = NULL, *cp, *ep;
size_t linesize = 0;
u_long linenum = 0;
u_int found_principal = 0;
if (authoptsp != NULL)
*authoptsp = NULL;
while (getline(&line, &linesize, f) != -1) {
linenum++;
/* Always consume entire input */
if (found_principal)
continue;
/* 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;
snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum);
if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0)
found_principal = 1;
}
free(line);
return found_principal;
}
/* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */
static int
match_principals_file(struct ssh *ssh, struct passwd *pw, char *file,
struct sshkey_cert *cert, struct sshauthopt **authoptsp)
{
FILE *f;
int success;
if (authoptsp != NULL)
*authoptsp = NULL;
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;
}
success = process_principals(ssh, f, file, cert, authoptsp);
fclose(f);
restore_uid();
return success;
}
/*
* Checks whether principal is allowed in output of command.
* returns 1 if the principal is allowed or 0 otherwise.
*/
static int
match_principals_command(struct ssh *ssh, struct passwd *user_pw,
const struct sshkey *key, struct sshauthopt **authoptsp)
{
struct passwd *runas_pw = NULL;
const struct sshkey_cert *cert = key->cert;
FILE *f = NULL;
int r, ok, found_principal = 0;
int i, ac = 0, uid_swapped = 0;
pid_t pid;
char *tmp, *username = NULL, *command = NULL, **av = NULL;
char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL;
char serial_s[32], uidstr[32];
void (*osigchld)(int);
if (authoptsp != NULL)
*authoptsp = NULL;
if (options.authorized_principals_command == NULL)
return 0;
if (options.authorized_principals_command_user == NULL) {
error("No user for AuthorizedPrincipalsCommand specified, "
"skipping");
return 0;
}
/*
* NB. all returns later this function should go via "out" to
* ensure the original SIGCHLD handler is restored properly.
*/
osigchld = ssh_signal(SIGCHLD, SIG_DFL);
/* Prepare and verify the user for the command */
username = percent_expand(options.authorized_principals_command_user,
"u", user_pw->pw_name, (char *)NULL);
runas_pw = getpwnam(username);
if (runas_pw == NULL) {
error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
username, strerror(errno));
goto out;
}
/* Turn the command into an argument vector */
if (argv_split(options.authorized_principals_command, &ac, &av) != 0) {
error("AuthorizedPrincipalsCommand \"%s\" contains "
"invalid quotes", options.authorized_principals_command);
goto out;
}
if (ac == 0) {
error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
options.authorized_principals_command);
goto out;
}
if ((ca_fp = sshkey_fingerprint(cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error_f("sshkey_fingerprint failed");
goto out;
}
if ((key_fp = sshkey_fingerprint(key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error_f("sshkey_fingerprint failed");
goto out;
}
if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
error_fr(r, "sshkey_to_base64 failed");
goto out;
}
if ((r = sshkey_to_base64(key, &keytext)) != 0) {
error_fr(r, "sshkey_to_base64 failed");
goto out;
}
snprintf(serial_s, sizeof(serial_s), "%llu",
(unsigned long long)cert->serial);
snprintf(uidstr, sizeof(uidstr), "%llu",
(unsigned long long)user_pw->pw_uid);
for (i = 1; i < ac; i++) {
tmp = percent_expand(av[i],
"U", uidstr,
"u", user_pw->pw_name,
"h", user_pw->pw_dir,
"t", sshkey_ssh_name(key),
"T", sshkey_ssh_name(cert->signature_key),
"f", key_fp,
"F", ca_fp,
"k", keytext,
"K", catext,
"i", cert->key_id,
"s", serial_s,
(char *)NULL);
if (tmp == NULL)
fatal_f("percent_expand failed");
free(av[i]);
av[i] = tmp;
}
/* Prepare a printable command for logs, etc. */
command = argv_assemble(ac, av);
if ((pid = subprocess("AuthorizedPrincipalsCommand", command,
ac, av, &f,
SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
runas_pw, temporarily_use_uid, restore_uid)) == 0)
goto out;
uid_swapped = 1;
temporarily_use_uid(runas_pw);
ok = process_principals(ssh, f, "(command)", cert, authoptsp);
fclose(f);
f = NULL;
if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0)
goto out;
/* Read completed successfully */
found_principal = ok;
out:
if (f != NULL)
fclose(f);
ssh_signal(SIGCHLD, osigchld);
for (i = 0; i < ac; i++)
free(av[i]);
free(av);
if (uid_swapped)
restore_uid();
free(command);
free(username);
free(ca_fp);
free(key_fp);
free(catext);
free(keytext);
return found_principal;
}
/*
* Check a single line of an authorized_keys-format file. Returns 0 if key
* matches, -1 otherwise. Will return key/cert options via *authoptsp
* on success. "loc" is used as file/line location in log messages.
*/
static int
check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
char *cp, const char *loc, struct sshauthopt **authoptsp)
{
int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type;
struct sshkey *found = NULL;
struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL;
char *key_options = NULL, *fp = NULL;
const char *reason = NULL;
int ret = -1;
if (authoptsp != NULL)
*authoptsp = NULL;
if ((found = sshkey_new(want_keytype)) == NULL) {
debug3_f("keytype %d failed", want_keytype);
goto out;
}
/* XXX djm: peek at key type in line and skip if unwanted */
if (sshkey_read(found, &cp) != 0) {
/* no key? check for options */
debug2("%s: check options: '%s'", loc, cp);
key_options = cp;
if (sshkey_advance_past_options(&cp) != 0) {
reason = "invalid key option string";
goto fail_reason;
}
skip_space(&cp);
if (sshkey_read(found, &cp) != 0) {
/* still no key? advance to next line*/
debug2("%s: advance: '%s'", loc, cp);
goto out;
}
}
/* Parse key options now; we need to know if this is a CA key */
if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) {
debug("%s: bad key options: %s", loc, reason);
auth_debug_add("%s: bad key options: %s", loc, reason);
goto out;
}
/* Ignore keys that don't match or incorrectly marked as CAs */
if (sshkey_is_cert(key)) {
/* Certificate; check signature key against CA */
if (!sshkey_equal(found, key->cert->signature_key) ||
!keyopts->cert_authority)
goto out;
} else {
/* Plain key: check it against key found in file */
if (!sshkey_equal(found, key) || keyopts->cert_authority)
goto out;
}
/* We have a candidate key, perform authorisation checks */
if ((fp = sshkey_fingerprint(found,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
fatal_f("fingerprint failed");
debug("%s: matching %s found: %s %s", loc,
sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp);
if (auth_authorise_keyopts(ssh, pw, keyopts,
sshkey_is_cert(key), loc) != 0) {
reason = "Refused by key options";
goto fail_reason;
}
/* That's all we need for plain keys. */
if (!sshkey_is_cert(key)) {
verbose("Accepted key %s %s found at %s",
sshkey_type(found), fp, loc);
finalopts = keyopts;
keyopts = NULL;
goto success;
}
/*
* Additional authorisation for certificates.
*/
/* Parse and check options present in certificate */
if ((certopts = sshauthopt_from_cert(key)) == NULL) {
reason = "Invalid certificate options";
goto fail_reason;
}
if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) {
reason = "Refused by certificate options";
goto fail_reason;
}
if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL)
goto fail_reason;
/*
* 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 (keyopts->cert_principals != NULL &&
!match_principals_option(keyopts->cert_principals, key->cert)) {
reason = "Certificate does not contain an authorized principal";
goto fail_reason;
}
if (sshkey_cert_check_authority(key, 0, 0,
keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0)
goto fail_reason;
verbose("Accepted certificate ID \"%s\" (serial %llu) "
"signed by CA %s %s found at %s",
key->cert->key_id,
(unsigned long long)key->cert->serial,
sshkey_type(found), fp, loc);
success:
if (finalopts == NULL)
fatal_f("internal error: missing options");
if (authoptsp != NULL) {
*authoptsp = finalopts;
finalopts = NULL;
}
/* success */
ret = 0;
goto out;
fail_reason:
error("%s", reason);
auth_debug_add("%s", reason);
out:
free(fp);
sshauthopt_free(keyopts);
sshauthopt_free(certopts);
sshauthopt_free(finalopts);
sshkey_free(found);
return ret;
}
/*
* 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(struct ssh *ssh, struct passwd *pw, FILE *f,
char *file, struct sshkey *key, struct sshauthopt **authoptsp)
{
char *cp, *line = NULL, loc[256];
size_t linesize = 0;
int found_key = 0;
u_long linenum = 0;
if (authoptsp != NULL)
*authoptsp = NULL;
while (getline(&line, &linesize, f) != -1) {
linenum++;
/* Always consume entire file */
if (found_key)
continue;
/* Skip leading whitespace, empty and comment lines. */
cp = line;
skip_space(&cp);
if (!*cp || *cp == '\n' || *cp == '#')
continue;
snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum);
if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0)
found_key = 1;
}
free(line);
return found_key;
}
/* Authenticate a certificate key against TrustedUserCAKeys */
static int
user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
struct sshauthopt **authoptsp)
{
char *ca_fp, *principals_file = NULL;
const char *reason;
struct sshauthopt *principals_opts = NULL, *cert_opts = NULL;
struct sshauthopt *final_opts = NULL;
int r, ret = 0, found_principal = 0, use_authorized_principals;
if (authoptsp != NULL)
*authoptsp = NULL;
if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL)
return 0;
if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
return 0;
if ((r = sshkey_in_file(key->cert->signature_key,
options.trusted_user_ca_keys, 1, 0)) != 0) {
debug2_fr(r, "CA %s %s is not listed in %s",
sshkey_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(ssh, pw, principals_file,
key->cert, &principals_opts))
found_principal = 1;
}
/* Try querying command if specified */
if (!found_principal && match_principals_command(ssh, pw, key,
&principals_opts))
found_principal = 1;
/* If principals file or command is specified, then require a match */
use_authorized_principals = principals_file != NULL ||
options.authorized_principals_command != NULL;
if (!found_principal && use_authorized_principals) {
reason = "Certificate does not contain an authorized principal";
goto fail_reason;
}
if (use_authorized_principals && principals_opts == NULL)
fatal_f("internal error: missing principals_opts");
if (sshkey_cert_check_authority(key, 0, 1,
use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
goto fail_reason;
/* Check authority from options in key and from principals file/cmd */
if ((cert_opts = sshauthopt_from_cert(key)) == NULL) {
reason = "Invalid certificate options";
goto fail_reason;
}
if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) {
reason = "Refused by certificate options";
goto fail_reason;
}
if (principals_opts == NULL) {
final_opts = cert_opts;
cert_opts = NULL;
} else {
if (auth_authorise_keyopts(ssh, pw, principals_opts, 0,
"principals") != 0) {
reason = "Refused by certificate principals options";
goto fail_reason;
}
if ((final_opts = sshauthopt_merge(principals_opts,
cert_opts, &reason)) == NULL) {
fail_reason:
error("%s", reason);
auth_debug_add("%s", reason);
goto out;
}
}
/* Success */
verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
"%s CA %s via %s", key->cert->key_id,
(unsigned long long)key->cert->serial,
sshkey_type(key->cert->signature_key), ca_fp,
options.trusted_user_ca_keys);
if (authoptsp != NULL) {
*authoptsp = final_opts;
final_opts = NULL;
}
ret = 1;
out:
sshauthopt_free(principals_opts);
sshauthopt_free(cert_opts);
sshauthopt_free(final_opts);
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 ssh *ssh, struct passwd *pw, struct sshkey *key,
char *file, struct sshauthopt **authoptsp)
{
FILE *f;
int found_key = 0;
if (authoptsp != NULL)
*authoptsp = NULL;
/* 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(ssh, pw, f, file,
key, authoptsp);
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 ssh *ssh, struct passwd *user_pw,
struct sshkey *key, struct sshauthopt **authoptsp)
{
struct passwd *runas_pw = NULL;
FILE *f = NULL;
int r, ok, found_key = 0;
int i, uid_swapped = 0, ac = 0;
pid_t pid;
char *username = NULL, *key_fp = NULL, *keytext = NULL;
char uidstr[32], *tmp, *command = NULL, **av = NULL;
void (*osigchld)(int);
if (authoptsp != NULL)
*authoptsp = NULL;
if (options.authorized_keys_command == NULL)
return 0;
if (options.authorized_keys_command_user == NULL) {
error("No user for AuthorizedKeysCommand specified, skipping");
return 0;
}
/*
* NB. all returns later this function should go via "out" to
* ensure the original SIGCHLD handler is restored properly.
*/
osigchld = ssh_signal(SIGCHLD, SIG_DFL);
/* Prepare and verify the user for the command */
username = percent_expand(options.authorized_keys_command_user,
"u", user_pw->pw_name, (char *)NULL);
runas_pw = getpwnam(username);
if (runas_pw == NULL) {
error("AuthorizedKeysCommandUser \"%s\" not found: %s",
username, strerror(errno));
goto out;
}
/* Prepare AuthorizedKeysCommand */
if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT)) == NULL) {
error_f("sshkey_fingerprint failed");
goto out;
}
if ((r = sshkey_to_base64(key, &keytext)) != 0) {
error_fr(r, "sshkey_to_base64 failed");
goto out;
}
/* Turn the command into an argument vector */
if (argv_split(options.authorized_keys_command, &ac, &av) != 0) {
error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
options.authorized_keys_command);
goto out;
}
if (ac == 0) {
error("AuthorizedKeysCommand \"%s\" yielded no arguments",
options.authorized_keys_command);
goto out;
}
snprintf(uidstr, sizeof(uidstr), "%llu",
(unsigned long long)user_pw->pw_uid);
for (i = 1; i < ac; i++) {
tmp = percent_expand(av[i],
"U", uidstr,
"u", user_pw->pw_name,
"h", user_pw->pw_dir,
"t", sshkey_ssh_name(key),
"f", key_fp,
"k", keytext,
(char *)NULL);
if (tmp == NULL)
fatal_f("percent_expand failed");
free(av[i]);
av[i] = tmp;
}
/* Prepare a printable command for logs, etc. */
command = argv_assemble(ac, av);
/*
* If AuthorizedKeysCommand was run without arguments
* then fall back to the old behaviour of passing the
* target username as a single argument.
*/
if (ac == 1) {
av = xreallocarray(av, ac + 2, sizeof(*av));
av[1] = xstrdup(user_pw->pw_name);
av[2] = NULL;
/* Fix up command too, since it is used in log messages */
free(command);
xasprintf(&command, "%s %s", av[0], av[1]);
}
if ((pid = subprocess("AuthorizedKeysCommand", command,
ac, av, &f,
SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
runas_pw, temporarily_use_uid, restore_uid)) == 0)
goto out;
uid_swapped = 1;
temporarily_use_uid(runas_pw);
ok = check_authkeys_file(ssh, user_pw, f,
options.authorized_keys_command, key, authoptsp);
fclose(f);
f = NULL;
if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0)
goto out;
/* Read completed successfully */
found_key = ok;
out:
if (f != NULL)
fclose(f);
ssh_signal(SIGCHLD, osigchld);
for (i = 0; i < ac; i++)
free(av[i]);
free(av);
if (uid_swapped)
restore_uid();
free(command);
free(username);
free(key_fp);
free(keytext);
return found_key;
}
/*
* Check whether key authenticates and authorises the user.
*/
int
user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
int auth_attempt, struct sshauthopt **authoptsp)
{
u_int success = 0, i;
char *file;
struct sshauthopt *opts = NULL;
if (authoptsp != NULL)
*authoptsp = NULL;
if (auth_key_is_revoked(key))
return 0;
if (sshkey_is_cert(key) &&
auth_key_is_revoked(key->cert->signature_key))
return 0;
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(ssh, pw, key, file, &opts);
free(file);
if (!success) {
sshauthopt_free(opts);
opts = NULL;
}
}
if (success)
goto out;
if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0)
goto out;
sshauthopt_free(opts);
opts = NULL;
if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0)
goto out;
sshauthopt_free(opts);
opts = NULL;
out:
if (success && authoptsp != NULL) {
*authoptsp = opts;
opts = NULL;
}
sshauthopt_free(opts);
return success;
}
Authmethod method_pubkey = {
"publickey",
userauth_pubkey,
&options.pubkey_authentication
};
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