- djm@cvs.openbsd.org 2012/10/30 21:29:55
[auth-rsa.c auth.c auth.h auth2-pubkey.c servconf.c servconf.h]
[sshd.c sshd_config sshd_config.5]
new sshd_config option AuthorizedKeysCommand to support fetching
authorized_keys from a command in addition to (or instead of) from
the filesystem. The command is run as the target server user unless
another specified via a new AuthorizedKeysCommandUser option.
patch originally by jchadima AT redhat.com, reworked by me; feedback
and ok markus@
diff --git a/ChangeLog b/ChangeLog
index 3cd16e4..27ec898 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,16 @@
- markus@cvs.openbsd.org 2012/10/05 12:34:39
[sftp.c]
fix signed vs unsigned warning; feedback & ok: djm@
+ - djm@cvs.openbsd.org 2012/10/30 21:29:55
+ [auth-rsa.c auth.c auth.h auth2-pubkey.c servconf.c servconf.h]
+ [sshd.c sshd_config sshd_config.5]
+ new sshd_config option AuthorizedKeysCommand to support fetching
+ authorized_keys from a command in addition to (or instead of) from
+ the filesystem. The command is run as the target server user unless
+ another specified via a new AuthorizedKeysCommandUser option.
+
+ patch originally by jchadima AT redhat.com, reworked by me; feedback
+ and ok markus@
20121019
- (tim) [buildpkg.sh.in] Double up on some backslashes so they end up in
diff --git a/auth-rsa.c b/auth-rsa.c
index 4ab46cd..2c8a7cb 100644
--- a/auth-rsa.c
+++ b/auth-rsa.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-rsa.c,v 1.80 2011/05/23 03:30:07 djm Exp $ */
+/* $OpenBSD: auth-rsa.c,v 1.81 2012/10/30 21:29:54 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -276,6 +276,8 @@
temporarily_use_uid(pw);
for (i = 0; !allowed && 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);
allowed = rsa_key_allowed_in_file(pw, file, client_n, rkey);
diff --git a/auth.c b/auth.c
index a8cffd5..b5e1eef 100644
--- a/auth.c
+++ b/auth.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.c,v 1.96 2012/05/13 01:42:32 dtucker Exp $ */
+/* $OpenBSD: auth.c,v 1.97 2012/10/30 21:29:54 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
@@ -409,41 +409,42 @@
return host_status;
}
-
/*
- * Check a given file for security. This is defined as all components
+ * Check a given path for security. This is defined as all components
* of the path to the file must be owned by either the owner of
* of the file or root and no directories must be group or world writable.
*
* XXX Should any specific check be done for sym links ?
*
- * Takes an open file descriptor, the file name, a uid and and
+ * Takes an the file name, its stat information (preferably from fstat() to
+ * avoid races), the uid of the expected owner, their home directory and an
* error buffer plus max size as arguments.
*
* Returns 0 on success and -1 on failure
*/
-static int
-secure_filename(FILE *f, const char *file, struct passwd *pw,
- char *err, size_t errlen)
+int
+auth_secure_path(const char *name, struct stat *stp, const char *pw_dir,
+ uid_t uid, char *err, size_t errlen)
{
- uid_t uid = pw->pw_uid;
char buf[MAXPATHLEN], homedir[MAXPATHLEN];
char *cp;
int comparehome = 0;
struct stat st;
- if (realpath(file, buf) == NULL) {
- snprintf(err, errlen, "realpath %s failed: %s", file,
+ if (realpath(name, buf) == NULL) {
+ snprintf(err, errlen, "realpath %s failed: %s", name,
strerror(errno));
return -1;
}
- if (realpath(pw->pw_dir, homedir) != NULL)
+ if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL)
comparehome = 1;
- /* check the open file to avoid races */
- if (fstat(fileno(f), &st) < 0 ||
- (st.st_uid != 0 && st.st_uid != uid) ||
- (st.st_mode & 022) != 0) {
+ if (!S_ISREG(stp->st_mode)) {
+ snprintf(err, errlen, "%s is not a regular file", buf);
+ return -1;
+ }
+ if ((stp->st_uid != 0 && stp->st_uid != uid) ||
+ (stp->st_mode & 022) != 0) {
snprintf(err, errlen, "bad ownership or modes for file %s",
buf);
return -1;
@@ -479,6 +480,28 @@
return 0;
}
+/*
+ * Version of secure_path() that accepts an open file descriptor to
+ * avoid races.
+ *
+ * Returns 0 on success and -1 on failure
+ */
+static int
+secure_filename(FILE *f, const char *file, struct passwd *pw,
+ char *err, size_t errlen)
+{
+ char buf[MAXPATHLEN];
+ struct stat st;
+
+ /* check the open file to avoid races */
+ if (fstat(fileno(f), &st) < 0) {
+ snprintf(err, errlen, "cannot stat file %s: %s",
+ buf, strerror(errno));
+ return -1;
+ }
+ return auth_secure_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen);
+}
+
static FILE *
auth_openfile(const char *file, struct passwd *pw, int strict_modes,
int log_missing, char *file_type)
diff --git a/auth.h b/auth.h
index 0d786c4..0634041 100644
--- a/auth.h
+++ b/auth.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.h,v 1.69 2011/05/23 03:30:07 djm Exp $ */
+/* $OpenBSD: auth.h,v 1.70 2012/10/30 21:29:54 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
@@ -120,6 +120,10 @@
int hostbased_key_allowed(struct passwd *, const char *, char *, Key *);
int user_key_allowed(struct passwd *, Key *);
+struct stat;
+int auth_secure_path(const char *, struct stat *, const char *, uid_t,
+ char *, size_t);
+
#ifdef KRB5
int auth_krb5(Authctxt *authctxt, krb5_data *auth, char **client, krb5_data *);
int auth_krb5_tgt(Authctxt *authctxt, krb5_data *tgt);
diff --git a/auth2-pubkey.c b/auth2-pubkey.c
index 5bccb5d..ec8f75d 100644
--- a/auth2-pubkey.c
+++ b/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.30 2011/09/25 05:44:47 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.31 2012/10/30 21:29:54 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
@@ -27,9 +27,13 @@
#include <sys/types.h>
#include <sys/stat.h>
+#include <sys/wait.h>
+#include <errno.h>
#include <fcntl.h>
+#include <paths.h>
#include <pwd.h>
+#include <signal.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
@@ -240,7 +244,7 @@
if (strcmp(cp, cert->principals[i]) == 0) {
debug3("matched principal \"%.100s\" "
"from file \"%s\" on line %lu",
- cert->principals[i], file, linenum);
+ cert->principals[i], file, linenum);
if (auth_parse_options(pw, line_opts,
file, linenum) != 1)
continue;
@@ -253,31 +257,22 @@
fclose(f);
restore_uid();
return 0;
-}
+}
-/* return 1 if user allows given key */
+/*
+ * Checks whether key is allowed in authorized_keys-format file,
+ * returns 1 if the key is allowed or 0 otherwise.
+ */
static int
-user_key_allowed2(struct passwd *pw, Key *key, char *file)
+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;
- FILE *f;
u_long linenum = 0;
Key *found;
char *fp;
- /* Temporarily use the user's uid. */
- temporarily_use_uid(pw);
-
- debug("trying public key file %s", file);
- f = auth_openkeyfile(file, pw, options.strict_modes);
-
- if (!f) {
- restore_uid();
- return 0;
- }
-
found_key = 0;
found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
@@ -370,8 +365,6 @@
break;
}
}
- restore_uid();
- fclose(f);
key_free(found);
if (!found_key)
debug2("key not found");
@@ -433,7 +426,172 @@
return ret;
}
-/* check whether given key is in .ssh/authorized_keys* */
+/*
+ * 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 errmsg[512];
+
+ if (options.authorized_keys_command == NULL ||
+ options.authorized_keys_command[0] != '/')
+ return 0;
+
+ /* If no user specified to run commands the default to target user */
+ if (options.authorized_keys_command_user == NULL)
+ pw = user_pw;
+ else {
+ pw = getpwnam(options.authorized_keys_command_user);
+ if (pw == NULL) {
+ error("AuthorizedKeyCommandUser \"%s\" not found: %s",
+ options.authorized_keys_command, strerror(errno));
+ return 0;
+ }
+ }
+
+ 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\" as \"%s\"",
+ options.authorized_keys_command, 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);
+
+ /* 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);
+ }
+
+ close(p[0]);
+ if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
+ error("%s: open %s: %s", __func__, _PATH_DEVNULL,
+ strerror(errno));
+ _exit(1);
+ }
+ if (dup2(devnull, STDIN_FILENO) == -1 ||
+ dup2(p[1], STDOUT_FILENO) == -1 ||
+ dup2(devnull, STDERR_FILENO) == -1) {
+ error("%s: dup2: %s", __func__, strerror(errno));
+ _exit(1);
+ }
+ closefrom(STDERR_FILENO + 1);
+
+ execl(options.authorized_keys_command,
+ options.authorized_keys_command, 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)
{
@@ -449,9 +607,17 @@
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);
xfree(file);
}
diff --git a/servconf.c b/servconf.c
index f4b7dd5..8e69ea5 100644
--- a/servconf.c
+++ b/servconf.c
@@ -1,5 +1,5 @@
-/* $OpenBSD: servconf.c,v 1.230 2012/09/13 23:37:36 dtucker Exp $ */
+/* $OpenBSD: servconf.c,v 1.231 2012/10/30 21:29:54 djm Exp $ */
/*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
@@ -135,6 +135,8 @@
options->num_permitted_opens = -1;
options->adm_forced_command = NULL;
options->chroot_directory = NULL;
+ options->authorized_keys_command = NULL;
+ options->authorized_keys_command_user = NULL;
options->zero_knowledge_password_authentication = -1;
options->revoked_keys_file = NULL;
options->trusted_user_ca_keys = NULL;
@@ -329,6 +331,7 @@
sZeroKnowledgePasswordAuthentication, sHostCertificate,
sRevokedKeys, sTrustedUserCAKeys, sAuthorizedPrincipalsFile,
sKexAlgorithms, sIPQoS, sVersionAddendum,
+ sAuthorizedKeysCommand, sAuthorizedKeysCommandUser,
sDeprecated, sUnsupported
} ServerOpCodes;
@@ -453,6 +456,8 @@
{ "authorizedprincipalsfile", sAuthorizedPrincipalsFile, SSHCFG_ALL },
{ "kexalgorithms", sKexAlgorithms, SSHCFG_GLOBAL },
{ "ipqos", sIPQoS, SSHCFG_ALL },
+ { "authorizedkeyscommand", sAuthorizedKeysCommand, SSHCFG_ALL },
+ { "authorizedkeyscommanduser", sAuthorizedKeysCommandUser, SSHCFG_ALL },
{ "versionaddendum", sVersionAddendum, SSHCFG_GLOBAL },
{ NULL, sBadOption, 0 }
};
@@ -1498,6 +1503,25 @@
}
return 0;
+ case sAuthorizedKeysCommand:
+ len = strspn(cp, WHITESPACE);
+ if (*activep && options->authorized_keys_command == NULL) {
+ if (cp[len] != '/' && strcasecmp(cp + len, "none") != 0)
+ fatal("%.200s line %d: AuthorizedKeysCommand "
+ "must be an absolute path",
+ filename, linenum);
+ options->authorized_keys_command = xstrdup(cp + len);
+ }
+ return 0;
+
+ case sAuthorizedKeysCommandUser:
+ charptr = &options->authorized_keys_command_user;
+
+ arg = strdelim(&cp);
+ if (*activep && *charptr == NULL)
+ *charptr = xstrdup(arg);
+ break;
+
case sDeprecated:
logit("%s line %d: Deprecated option %s",
filename, linenum, arg);
@@ -1648,6 +1672,8 @@
M_CP_INTOPT(hostbased_uses_name_from_packet_only);
M_CP_INTOPT(kbd_interactive_authentication);
M_CP_INTOPT(zero_knowledge_password_authentication);
+ M_CP_STROPT(authorized_keys_command);
+ M_CP_STROPT(authorized_keys_command_user);
M_CP_INTOPT(permit_root_login);
M_CP_INTOPT(permit_empty_passwd);
@@ -1908,6 +1934,8 @@
dump_cfg_string(sAuthorizedPrincipalsFile,
o->authorized_principals_file);
dump_cfg_string(sVersionAddendum, o->version_addendum);
+ dump_cfg_string(sAuthorizedKeysCommand, o->authorized_keys_command);
+ dump_cfg_string(sAuthorizedKeysCommandUser, o->authorized_keys_command_user);
/* string arguments requiring a lookup */
dump_cfg_string(sLogLevel, log_level_name(o->log_level));
diff --git a/servconf.h b/servconf.h
index 096d596..0064c9b 100644
--- a/servconf.h
+++ b/servconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.h,v 1.103 2012/07/10 02:19:15 djm Exp $ */
+/* $OpenBSD: servconf.h,v 1.104 2012/10/30 21:29:55 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -166,6 +166,8 @@
char *revoked_keys_file;
char *trusted_user_ca_keys;
char *authorized_principals_file;
+ char *authorized_keys_command;
+ char *authorized_keys_command_user;
char *version_addendum; /* Appended to SSH banner */
} ServerOptions;
diff --git a/sshd.c b/sshd.c
index 9aff5e8..eff0290 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.393 2012/07/10 02:19:15 djm Exp $ */
+/* $OpenBSD: sshd.c,v 1.394 2012/10/30 21:29:55 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -359,6 +359,15 @@
if (use_privsep && pmonitor != NULL && pmonitor->m_pid > 0)
kill(pmonitor->m_pid, SIGALRM);
+ /*
+ * Try to kill any processes that we have spawned, E.g. authorized
+ * keys command helpers.
+ */
+ if (getpgid(0) == getpid()) {
+ signal(SIGTERM, SIG_IGN);
+ killpg(0, SIGTERM);
+ }
+
/* Log error and exit. */
sigdie("Timeout before authentication for %s", get_remote_ipaddr());
}
diff --git a/sshd_config b/sshd_config
index 9424ee2..3d35bef 100644
--- a/sshd_config
+++ b/sshd_config
@@ -1,4 +1,4 @@
-# $OpenBSD: sshd_config,v 1.87 2012/07/10 02:19:15 djm Exp $
+# $OpenBSD: sshd_config,v 1.88 2012/10/30 21:29:55 djm Exp $
# This is the sshd server system-wide configuration file. See
# sshd_config(5) for more information.
@@ -51,6 +51,9 @@
#AuthorizedPrincipalsFile none
+#AuthorizedKeysCommand none
+#AuthorizedKeysCommandUser nobody
+
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no
# similar for protocol version 2
diff --git a/sshd_config.5 b/sshd_config.5
index 987558a..de8f0f8 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.\" $OpenBSD: sshd_config.5,v 1.145 2012/10/04 13:21:50 markus Exp $
-.Dd $Mdocdate: October 4 2012 $
+.\" $OpenBSD: sshd_config.5,v 1.146 2012/10/30 21:29:55 djm Exp $
+.Dd $Mdocdate: October 30 2012 $
.Dt SSHD_CONFIG 5
.Os
.Sh NAME
@@ -151,6 +151,22 @@
in
.Xr ssh_config 5
for more information on patterns.
+.It Cm AuthorizedKeysCommand
+Specifies a program to be used for lookup of the user's public keys.
+The program will be invoked with a single argument of the username
+being authenticated, and should produce on standard output zero or
+more lines of authorized_keys output (see AUTHORIZED_KEYS in
+.Xr sshd 8 )
+If a key supplied by AuthorizedKeysCommand does not successfully authenticate
+and authorize the user then public key authentication continues using the usual
+.Cm AuthorizedKeysFile
+files.
+By default, no AuthorizedKeysCommand is run.
+.It Cm AuthorizedKeysCommandUser
+Specifies the user under whose account the AuthorizedKeysCommand is run.
+The default is the user being authenticated.
+It is recommended to use a dedicated user that has no other role on the host
+than running authorized keys commands.
.It Cm AuthorizedKeysFile
Specifies the file that contains the public keys that can be used
for user authentication.
@@ -712,6 +728,8 @@
.Cm AllowTcpForwarding ,
.Cm AllowUsers ,
.Cm AuthorizedKeysFile ,
+.Cm AuthorizedKeysCommand ,
+.Cm AuthorizedKeysCommandUser ,
.Cm AuthorizedPrincipalsFile ,
.Cm Banner ,
.Cm ChrootDirectory ,