/* $OpenBSD: auth2-pubkeyfile.c,v 1.4 2023/03/05 05:34:09 dtucker Exp $ */

/*

* Copyright (c) 2000 Markus Friedl. All rights reserved.

* Copyright (c) 2010 Damien Miller. 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>

#include <pwd.h>

#include <stdio.h>

#include <stdarg.h>

#include <string.h>

#include <time.h>

#include <unistd.h>

#include "ssh.h"

#include "log.h"

#include "misc.h"

#include "sshkey.h"

#include "digest.h"

#include "hostfile.h"

#include "auth.h"

#include "auth-options.h"

#include "authfile.h"

#include "match.h"

#include "ssherr.h"

int

auth_authorise_keyopts(struct passwd *pw, struct sshauthopt *opts,

int allow_cert_authority, const char *remote_ip, const char *remote_host,

const char *loc)

{

time_t now = time(NULL);

char buf[64];

/*

* Check keys/principals file expiry time.

* NB. validity interval in certificate is handled elsewhere.

*/

if (opts->valid_before && now > 0 &&

opts->valid_before < (uint64_t)now) {

format_absolute_time(opts->valid_before, buf, sizeof(buf));

debug("%s: entry expired at %s", loc, buf);

auth_debug_add("%s: entry expired at %s", loc, buf);

return -1;

}

/* Consistency checks */

if (opts->cert_principals != NULL && !opts->cert_authority) {

debug("%s: principals on non-CA key", loc);

auth_debug_add("%s: principals on non-CA key", loc);

/* deny access */

return -1;

}

/* cert-authority flag isn't valid in authorized_principals files */

if (!allow_cert_authority && opts->cert_authority) {

debug("%s: cert-authority flag invalid here", loc);

auth_debug_add("%s: cert-authority flag invalid here", loc);

/* deny access */

return -1;

}

/* Perform from= checks */

if (opts->required_from_host_keys != NULL) {

switch (match_host_and_ip(remote_host, remote_ip,

opts->required_from_host_keys )) {

case 1:

/* Host name matches. */

break;

case -1:

default:

debug("%s: invalid from criteria", loc);

auth_debug_add("%s: invalid from criteria", loc);

/* FALLTHROUGH */

case 0:

logit("%s: Authentication tried for %.100s with "

"correct key but not from a permitted "

"host (host=%.200s, ip=%.200s, required=%.200s).",

loc, pw->pw_name, remote_host, remote_ip,

opts->required_from_host_keys);

auth_debug_add("%s: Your host '%.200s' is not "

"permitted to use this key for login.",

loc, remote_host);

/* deny access */

return -1;

}

}

/* Check source-address restriction from certificate */

if (opts->required_from_host_cert != NULL) {

switch (addr_match_cidr_list(remote_ip,

opts->required_from_host_cert)) {

case 1:

/* accepted */

break;

case -1:

default:

/* invalid */

error("%s: Certificate source-address invalid", loc);

/* FALLTHROUGH */

case 0:

logit("%s: Authentication tried for %.100s with valid "

"certificate but not from a permitted source "

"address (%.200s).", loc, pw->pw_name, remote_ip);

auth_debug_add("%s: Your address '%.200s' is not "

"permitted to use this certificate for login.",

loc, remote_ip);

return -1;

}

}

/*

*

* XXX this is spammy. We should report remotely only for keys

* that are successful in actual auth attempts, and not PK_OK

* tests.

*/

auth_log_authopts(loc, opts, 1);

return 0;

}

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.

*/

int

auth_check_principals_line(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;

}

int

auth_process_principals(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, nonblank = 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;

nonblank++;

snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum);

if (auth_check_principals_line(cp, cert, loc, authoptsp) == 0)

found_principal = 1;

}

debug2_f("%s: processed %lu/%lu lines", file, nonblank, linenum);

free(line);

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.

*/

int

auth_check_authkey_line(struct passwd *pw, struct sshkey *key,

char *cp, const char *remote_ip, const char *remote_host, 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,

SSH_FP_HASH_DEFAULT, 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(pw, keyopts,

sshkey_is_cert(key), remote_ip, remote_host, 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(pw, certopts, 0,

remote_ip, remote_host, 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_now(key, 0, 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.

*/

int

auth_check_authkeys_file(struct passwd *pw, FILE *f, char *file,

struct sshkey *key, const char *remote_ip,

const char *remote_host, struct sshauthopt **authoptsp)

{

char *cp, *line = NULL, loc[256];

size_t linesize = 0;

int found_key = 0;

u_long linenum = 0, nonblank = 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;

nonblank++;

snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum);

if (auth_check_authkey_line(pw, key, cp,

remote_ip, remote_host, loc, authoptsp) == 0)

found_key = 1;

}

free(line);

debug2_f("%s: processed %lu/%lu lines", file, nonblank, linenum);

return found_key;

}

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 (errno != ENOENT) {

logit("Could not open user '%s' %s '%s': %s",

pw->pw_name, file_type, file, strerror(errno));

} else if (log_missing) {

debug("Could not open user '%s' %s '%s': %s",

pw->pw_name, file_type, file, strerror(errno));

}

return NULL;

}

if (fstat(fd, &st) == -1) {

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");

}