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openssh/auth2-pubkey.c

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/* $OpenBSD: auth2-pubkey.c,v 1.62 2017/01/30 01:03:00 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/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 <limits.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"
#include "ssherr.h"
#include "channels.h" /* XXX for session.h */
#include "session.h" /* XXX for child_set_env(); refactor? */
/* 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, *fp = NULL;
u_char *pkblob, *sig;
u_int alen, blen, slen;
int have_sig, pktype;
int authenticated = 0;
if (!authctxt->valid) {
debug2("%s: disabled because of invalid user", __func__);
return 0;
}
have_sig = packet_get_char();
if (datafellows & SSH_BUG_PKAUTH) {
debug2("%s: SSH_BUG_PKAUTH", __func__);
/* 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("%s: unsupported public key algorithm: %s",
__func__, pkalg);
goto done;
}
key = key_from_blob(pkblob, blen);
if (key == NULL) {
error("%s: cannot decode key: %s", __func__, pkalg);
goto done;
}
if (key->type != pktype) {
error("%s: type mismatch for decoded key "
"(received %d, expected %d)", __func__, 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;
}
fp = sshkey_fingerprint(key, options.fingerprint_hash, SSH_FP_DEFAULT);
if (auth2_userkey_already_used(authctxt, key)) {
logit("refusing previously-used %s key", key_type(key));
goto done;
}
if (match_pattern_list(sshkey_ssh_name(key),
options.pubkey_key_types, 0) != 1) {
logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
__func__, sshkey_ssh_name(key));
goto done;
}
if (have_sig) {
debug3("%s: have signature for %s %s",
__func__, sshkey_type(key), fp);
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, 1)) &&
PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
buffer_len(&b))) == 1) {
authenticated = 1;
/* Record the successful key to prevent reuse */
auth2_record_userkey(authctxt, key);
key = NULL; /* Don't free below */
}
buffer_free(&b);
free(sig);
} else {
debug("%s: test whether pkalg/pkblob are acceptable for %s %s",
__func__, sshkey_type(key), fp);
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, 0))) {
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("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg);
if (key != NULL)
key_free(key);
free(pkalg);
free(pkblob);
free(fp);
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 = sshkey_fingerprint(key->cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT);
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 == NULL ? "(null)" : fp,
extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
free(fp);
} else {
fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT);
auth_info(authctxt, "%s %s%s%s", key_type(key),
fp == NULL ? "(null)" : fp,
extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
free(fp);
}
free(extra);
}
/*
* Splits 's' into an argument vector. Handles quoted string and basic
* escape characters (\\, \", \'). Caller must free the argument vector
* and its members.
*/
static int
split_argv(const char *s, int *argcp, char ***argvp)
{
int r = SSH_ERR_INTERNAL_ERROR;
int argc = 0, quote, i, j;
char *arg, **argv = xcalloc(1, sizeof(*argv));
*argvp = NULL;
*argcp = 0;
for (i = 0; s[i] != '\0'; i++) {
/* Skip leading whitespace */
if (s[i] == ' ' || s[i] == '\t')
continue;
/* Start of a token */
quote = 0;
if (s[i] == '\\' &&
(s[i + 1] == '\'' || s[i + 1] == '\"' || s[i + 1] == '\\'))
i++;
else if (s[i] == '\'' || s[i] == '"')
quote = s[i++];
argv = xreallocarray(argv, (argc + 2), sizeof(*argv));
arg = argv[argc++] = xcalloc(1, strlen(s + i) + 1);
argv[argc] = NULL;
/* Copy the token in, removing escapes */
for (j = 0; s[i] != '\0'; i++) {
if (s[i] == '\\') {
if (s[i + 1] == '\'' ||
s[i + 1] == '\"' ||
s[i + 1] == '\\') {
i++; /* Skip '\' */
arg[j++] = s[i];
} else {
/* Unrecognised escape */
arg[j++] = s[i];
}
} else if (quote == 0 && (s[i] == ' ' || s[i] == '\t'))
break; /* done */
else if (quote != 0 && s[i] == quote)
break; /* done */
else
arg[j++] = s[i];
}
if (s[i] == '\0') {
if (quote != 0) {
/* Ran out of string looking for close quote */
r = SSH_ERR_INVALID_FORMAT;
goto out;
}
break;
}
}
/* Success */
*argcp = argc;
*argvp = argv;
argc = 0;
argv = NULL;
r = 0;
out:
if (argc != 0 && argv != NULL) {
for (i = 0; i < argc; i++)
free(argv[i]);
free(argv);
}
return r;
}
/*
* Reassemble an argument vector into a string, quoting and escaping as
* necessary. Caller must free returned string.
*/
static char *
assemble_argv(int argc, char **argv)
{
int i, j, ws, r;
char c, *ret;
struct sshbuf *buf, *arg;
if ((buf = sshbuf_new()) == NULL || (arg = sshbuf_new()) == NULL)
fatal("%s: sshbuf_new failed", __func__);
for (i = 0; i < argc; i++) {
ws = 0;
sshbuf_reset(arg);
for (j = 0; argv[i][j] != '\0'; j++) {
r = 0;
c = argv[i][j];
switch (c) {
case ' ':
case '\t':
ws = 1;
r = sshbuf_put_u8(arg, c);
break;
case '\\':
case '\'':
case '"':
if ((r = sshbuf_put_u8(arg, '\\')) != 0)
break;
/* FALLTHROUGH */
default:
r = sshbuf_put_u8(arg, c);
break;
}
if (r != 0)
fatal("%s: sshbuf_put_u8: %s",
__func__, ssh_err(r));
}
if ((i != 0 && (r = sshbuf_put_u8(buf, ' ')) != 0) ||
(ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0) ||
(r = sshbuf_putb(buf, arg)) != 0 ||
(ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0))
fatal("%s: buffer error: %s", __func__, ssh_err(r));
}
if ((ret = malloc(sshbuf_len(buf) + 1)) == NULL)
fatal("%s: malloc failed", __func__);
memcpy(ret, sshbuf_ptr(buf), sshbuf_len(buf));
ret[sshbuf_len(buf)] = '\0';
sshbuf_free(buf);
sshbuf_free(arg);
return ret;
}
/*
* Runs command in a subprocess. Returns pid on success and a FILE* to the
* subprocess' stdout or 0 on failure.
* NB. "command" is only used for logging.
*/
static pid_t
subprocess(const char *tag, struct passwd *pw, const char *command,
int ac, char **av, FILE **child)
{
FILE *f;
struct stat st;
int devnull, p[2], i;
pid_t pid;
char *cp, errmsg[512];
u_int envsize;
char **child_env;
*child = NULL;
debug3("%s: %s command \"%s\" running as %s", __func__,
tag, command, pw->pw_name);
/* Verify the path exists and is 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 (auth_secure_path(av[0], &st, NULL, 0,
errmsg, sizeof(errmsg)) != 0) {
error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
restore_uid();
return 0;
}
/*
* Run the command; stderr is left in place, stdout is the
* authorized_keys output.
*/
if (pipe(p) != 0) {
error("%s: pipe: %s", tag, strerror(errno));
restore_uid();
return 0;
}
/*
* 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", 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);
}
/* 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", 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 (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 ((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)
;
return 0;
}
/* Success */
debug3("%s: %s pid %ld", __func__, tag, (long)pid);
*child = f;
return pid;
}
/* Returns 0 if pid exited cleanly, non-zero otherwise */
static int
exited_cleanly(pid_t pid, const char *tag, const char *cmd)
{
int status;
while (waitpid(pid, &status, 0) == -1) {
if (errno != EINTR) {
error("%s: waitpid: %s", tag, strerror(errno));
return -1;
}
}
if (WIFSIGNALED(status)) {
error("%s %s exited on signal %d", tag, cmd, WTERMSIG(status));
return -1;
} else if (WEXITSTATUS(status) != 0) {
error("%s %s failed, status %d", tag, cmd, WEXITSTATUS(status));
return -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;
}
static int
process_principals(FILE *f, char *file, struct passwd *pw,
const struct sshkey_cert *cert)
{
char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
u_long linenum = 0;
u_int i, found_principal = 0;
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
/* 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;
/* 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("%s:%lu: matched principal \"%.100s\"",
file == NULL ? "(command)" : file,
linenum, cert->principals[i]);
if (auth_parse_options(pw, line_opts,
file, linenum) != 1)
continue;
found_principal = 1;
continue;
}
}
}
return found_principal;
}
static int
match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
{
FILE *f;
int success;
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(f, file, pw, cert);
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 passwd *user_pw, const struct sshkey *key)
{
const struct sshkey_cert *cert = key->cert;
FILE *f = NULL;
int r, ok, found_principal = 0;
struct passwd *pw;
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[16];
void (*osigchld)(int);
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 = 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);
pw = getpwnam(username);
if (pw == NULL) {
error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
username, strerror(errno));
goto out;
}
/* Turn the command into an argument vector */
if (split_argv(options.authorized_principals_command, &ac, &av) != 0) {
error("AuthorizedPrincipalsCommand \"%s\" contains "
"invalid quotes", command);
goto out;
}
if (ac == 0) {
error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
command);
goto out;
}
if ((ca_fp = sshkey_fingerprint(cert->signature_key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: sshkey_fingerprint failed", __func__);
goto out;
}
if ((key_fp = sshkey_fingerprint(key,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
error("%s: sshkey_fingerprint failed", __func__);
goto out;
}
if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
goto out;
}
if ((r = sshkey_to_base64(key, &keytext)) != 0) {
error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
goto out;
}
snprintf(serial_s, sizeof(serial_s), "%llu",
(unsigned long long)cert->serial);
for (i = 1; i < ac; i++) {
tmp = percent_expand(av[i],
"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("%s: percent_expand failed", __func__);
free(av[i]);
av[i] = tmp;
}
/* Prepare a printable command for logs, etc. */
command = assemble_argv(ac, av);
if ((pid = subprocess("AuthorizedPrincipalsCommand", pw, command,
ac, av, &f)) == 0)
goto out;
uid_swapped = 1;
temporarily_use_uid(pw);
ok = process_principals(f, NULL, pw, cert);
fclose(f);
f = NULL;
if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command) != 0)
goto out;
/* Read completed successfully */
found_principal = ok;
out:
if (f != NULL)
fclose(f);
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;
}
/*
* 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];
int found_key = 0;
u_long linenum = 0;
Key *found;
found_key = 0;
found = NULL;
while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
char *cp, *key_options = NULL, *fp = NULL;
const char *reason = NULL;
/* Always consume entrire file */
if (found_key)
continue;
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;
if ((fp = sshkey_fingerprint(found,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
continue;
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, &reason) != 0)
goto fail_reason;
verbose("Accepted certificate ID \"%s\" (serial %llu) "
"signed by %s CA %s via %s", key->cert->key_id,
(unsigned long long)key->cert->serial,
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;
if ((fp = sshkey_fingerprint(found,
options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
continue;
debug("matching key found: file %s, line %lu %s %s",
file, linenum, key_type(found), fp);
free(fp);
found_key = 1;
continue;
}
}
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, found_principal = 0, use_authorized_principals;
if (!key_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 (sshkey_in_file(key->cert->signature_key,
options.trusted_user_ca_keys, 1, 0) != 0) {
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))
found_principal = 1;
}
/* Try querying command if specified */
if (!found_principal && match_principals_command(pw, key))
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";
fail_reason:
error("%s", reason);
auth_debug_add("%s", reason);
goto out;
}
if (key_cert_check_authority(key, 0, 1,
use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
goto fail_reason;
if (auth_cert_options(key, pw, &reason) != 0)
goto fail_reason;
verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
"%s CA %s via %s", key->cert->key_id,
(unsigned long long)key->cert->serial,
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 = NULL;
int r, ok, found_key = 0;
struct passwd *pw;
int i, uid_swapped = 0, ac = 0;
pid_t pid;
char *username = NULL, *key_fp = NULL, *keytext = NULL;
char *tmp, *command = NULL, **av = NULL;
void (*osigchld)(int);
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 = 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);
pw = getpwnam(username);
if (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("%s: sshkey_fingerprint failed", __func__);
goto out;
}
if ((r = sshkey_to_base64(key, &keytext)) != 0) {
error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
goto out;
}
/* Turn the command into an argument vector */
if (split_argv(options.authorized_keys_command, &ac, &av) != 0) {
error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
command);
goto out;
}
if (ac == 0) {
error("AuthorizedKeysCommand \"%s\" yielded no arguments",
command);
goto out;
}
for (i = 1; i < ac; i++) {
tmp = percent_expand(av[i],
"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("%s: percent_expand failed", __func__);
free(av[i]);
av[i] = tmp;
}
/* Prepare a printable command for logs, etc. */
command = assemble_argv(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", pw, command,
ac, av, &f)) == 0)
goto out;
uid_swapped = 1;
temporarily_use_uid(pw);
ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
fclose(f);
f = NULL;
if (exited_cleanly(pid, "AuthorizedKeysCommand", command) != 0)
goto out;
/* Read completed successfully */
found_key = ok;
out:
if (f != NULL)
fclose(f);
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 passwd *pw, Key *key, int auth_attempt)
{
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;
}
/* Records a public key in the list of previously-successful keys */
void
auth2_record_userkey(Authctxt *authctxt, struct sshkey *key)
{
struct sshkey **tmp;
if (authctxt->nprev_userkeys >= INT_MAX ||
(tmp = reallocarray(authctxt->prev_userkeys,
authctxt->nprev_userkeys + 1, sizeof(*tmp))) == NULL)
fatal("%s: reallocarray failed", __func__);
authctxt->prev_userkeys = tmp;
authctxt->prev_userkeys[authctxt->nprev_userkeys] = key;
authctxt->nprev_userkeys++;
}
/* Checks whether a key has already been used successfully for authentication */
int
auth2_userkey_already_used(Authctxt *authctxt, struct sshkey *key)
{
u_int i;
for (i = 0; i < authctxt->nprev_userkeys; i++) {
if (sshkey_equal_public(key, authctxt->prev_userkeys[i])) {
return 1;
}
}
return 0;
}
Authmethod method_pubkey = {
"publickey",
userauth_pubkey,
&options.pubkey_authentication
};
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