upstream: Let allowed signers files used by ssh-keygen(1)

signatures support key lifetimes, and allow the verification mode to specify
a signature time to check at. This is intended for use by git to support
signing objects using ssh keys. ok dtucker@

OpenBSD-Commit-ID: 3e2c67b7dcd94f0610194d1e8e4907829a40cf31

auth2-hostbased.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-hostbased.c,v 1.46 2021/01/27 10:05:28 djm Exp $ */
+/* $OpenBSD: auth2-hostbased.c,v 1.47 2021/07/23 03:37:52 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -213,7 +213,7 @@ hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
 	debug2_f("access allowed by auth_rhosts2");
 
 	if (sshkey_is_cert(key) &&
-	    sshkey_cert_check_authority(key, 1, 0, 0, lookup, &reason)) {
+	    sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) {
 		error("%s", reason);
 		auth_debug_add("%s", reason);
 		return 0;

auth2-pubkey.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.108 2021/06/08 06:54:40 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.109 2021/07/23 03:37:52 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -674,7 +674,7 @@ check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
 		reason = "Certificate does not contain an authorized principal";
 		goto fail_reason;
 	}
-	if (sshkey_cert_check_authority(key, 0, 0, 0,
+	if (sshkey_cert_check_authority_now(key, 0, 0, 0,
 	    keyopts->cert_principals == NULL ? pw->pw_name : NULL,
 	    &reason) != 0)
 		goto fail_reason;
@@ -794,7 +794,7 @@ user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
 	}
 	if (use_authorized_principals && principals_opts == NULL)
 		fatal_f("internal error: missing principals_opts");
-	if (sshkey_cert_check_authority(key, 0, 1, 0,
+	if (sshkey_cert_check_authority_now(key, 0, 1, 0,
 	    use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
 		goto fail_reason;
 

ssh-keygen.1

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ssh-keygen.1,v 1.213 2021/05/12 11:34:30 dtucker Exp $
+.\"	$OpenBSD: ssh-keygen.1,v 1.214 2021/07/23 03:37:52 djm Exp $
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -35,7 +35,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: May 12 2021 $
+.Dd $Mdocdate: July 23 2021 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
@@ -147,10 +147,12 @@
 .Ar
 .Nm ssh-keygen
 .Fl Y Cm find-principals
+.Op Fl O Ar option
 .Fl s Ar signature_file
 .Fl f Ar allowed_signers_file
 .Nm ssh-keygen
 .Fl Y Cm check-novalidate
+.Op Fl O Ar option
 .Fl n Ar namespace
 .Fl s Ar signature_file
 .Nm ssh-keygen
@@ -160,6 +162,7 @@
 .Ar
 .Nm ssh-keygen
 .Fl Y Cm verify
+.Op Fl O Ar option
 .Fl f Ar allowed_signers_file
 .Fl I Ar signer_identity
 .Fl n Ar namespace
@@ -530,6 +533,17 @@ Please note that this information is potentially sensitive.
 By default, this information is discarded.
 .El
 .Pp
+When performing signature-related options using the
+.Fl Y
+flag, the following options are accepted:
+.Bl -tag -width Ds
+.It Cm verify-time Ns = Ns Ar timestamp
+Specifies a time to use when validating signatures instead of the current
+time.
+The time may be specified as a date in YYYYMMDD format or a time
+in YYYYMMDDHHMM[SS] format.
+.El
+.Pp
 The
 .Fl O
 option may be specified multiple times.
@@ -1134,11 +1148,16 @@ are case-insensitive):
 .It Cm cert-authority
 Indicates that this key is accepted as a certificate authority (CA) and
 that certificates signed by this CA may be accepted for verification.
-.It Cm namespaces="namespace-list"
+.It Cm namespaces Ns = Ns "namespace-list"
 Specifies a pattern-list of namespaces that are accepted for this key.
 If this option is present, the signature namespace embedded in the
 signature object and presented on the verification command-line must
 match the specified list before the key will be considered acceptable.
+.It Cm valid-after Ns = Ns "timestamp"
+Indicates that the key is valid for use at or after the specified timestamp,
+which may be a date in YYYYMMDD format or a time in YYYYMMDDHHMM[SS] format,
+.It Cm valid-before Ns = Ns "timestamp"
+Indicates that the key is valid for use at or before the specified timestamp.
 .El
 .Pp
 When verifying signatures made by certificates, the expected principal

ssh-keygen.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.431 2021/07/09 09:55:56 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.432 2021/07/23 03:37:52 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -2672,15 +2672,49 @@ done:
 	return ret;
 }
 
+static int
+sig_process_opts(char * const *opts, size_t nopts, uint64_t *verify_timep)
+{
+	size_t i;
+	time_t now;
+
+	*verify_timep = 0;
+	for (i = 0; i < nopts; i++) {
+		if (strncasecmp(opts[i], "verify-time=", 12) == 0) {
+			if (parse_absolute_time(opts[i] + 12,
+			    verify_timep) != 0 || *verify_timep == 0) {
+				error("Invalid \"verify-time\" option");
+				return SSH_ERR_INVALID_ARGUMENT;
+			}
+		} else {
+			error("Invalid option \"%s\"", opts[i]);
+			return SSH_ERR_INVALID_ARGUMENT;
+		}
+	}
+	if (*verify_timep == 0) {
+		if ((now = time(NULL)) < 0) {
+			error("Time is before epoch");
+			return SSH_ERR_INVALID_ARGUMENT;
+		}
+		*verify_timep = (uint64_t)now;
+	}
+	return 0;
+}
+
 static int
 sig_verify(const char *signature, const char *sig_namespace,
-    const char *principal, const char *allowed_keys, const char *revoked_keys)
+    const char *principal, const char *allowed_keys, const char *revoked_keys,
+    char * const *opts, size_t nopts)
 {
 	int r, ret = -1;
 	struct sshbuf *sigbuf = NULL, *abuf = NULL;
 	struct sshkey *sign_key = NULL;
 	char *fp = NULL;
 	struct sshkey_sig_details *sig_details = NULL;
+	uint64_t verify_time = 0;
+
+	if (sig_process_opts(opts, nopts, &verify_time) != 0)
+		goto done; /* error already logged */
 
 	memset(&sig_details, 0, sizeof(sig_details));
 	if ((r = sshbuf_load_file(signature, &abuf)) != 0) {
@@ -2715,7 +2749,7 @@ sig_verify(const char *signature, const char *sig_namespace,
 	}
 
 	if (allowed_keys != NULL && (r = sshsig_check_allowed_keys(allowed_keys,
-	    sign_key, principal, sig_namespace)) != 0) {
+	    sign_key, principal, sig_namespace, verify_time)) != 0) {
 		debug3_fr(r, "sshsig_check_allowed_keys");
 		goto done;
 	}
@@ -2749,11 +2783,17 @@ done:
 }
 
 static int
-sig_find_principals(const char *signature, const char *allowed_keys) {
+sig_find_principals(const char *signature, const char *allowed_keys,
+    char * const *opts, size_t nopts)
+{
 	int r, ret = -1;
 	struct sshbuf *sigbuf = NULL, *abuf = NULL;
 	struct sshkey *sign_key = NULL;
 	char *principals = NULL, *cp, *tmp;
+	uint64_t verify_time = 0;
+
+	if (sig_process_opts(opts, nopts, &verify_time) != 0)
+		goto done; /* error already logged */
 
 	if ((r = sshbuf_load_file(signature, &abuf)) != 0) {
 		error_r(r, "Couldn't read signature file");
@@ -2768,7 +2808,7 @@ sig_find_principals(const char *signature, const char *allowed_keys) {
 		goto done;
 	}
 	if ((r = sshsig_find_principals(allowed_keys, sign_key,
-	    &principals)) != 0) {
+	    verify_time, &principals)) != 0) {
 		if (r != SSH_ERR_KEY_NOT_FOUND)
 			error_fr(r, "sshsig_find_principal");
 		goto done;
@@ -3380,7 +3420,8 @@ main(int argc, char **argv)
 				    "missing allowed keys file");
 				exit(1);
 			}
-			return sig_find_principals(ca_key_path, identity_file);
+			return sig_find_principals(ca_key_path, identity_file,
+			    opts, nopts);
 		} else if (strncmp(sign_op, "sign", 4) == 0) {
 			if (cert_principals == NULL ||
 			    *cert_principals == '\0') {
@@ -3402,7 +3443,7 @@ main(int argc, char **argv)
 				exit(1);
 			}
 			return sig_verify(ca_key_path, cert_principals,
-			    NULL, NULL, NULL);
+			    NULL, NULL, NULL, opts, nopts);
 		} else if (strncmp(sign_op, "verify", 6) == 0) {
 			if (cert_principals == NULL ||
 			    *cert_principals == '\0') {
@@ -3426,7 +3467,8 @@ main(int argc, char **argv)
 				exit(1);
 			}
 			return sig_verify(ca_key_path, cert_principals,
-			    cert_key_id, identity_file, rr_hostname);
+			    cert_key_id, identity_file, rr_hostname,
+			    opts, nopts);
 		}
 		error("Unsupported operation for -Y: \"%s\"", sign_op);
 		usage();

sshkey.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.118 2021/07/12 06:08:57 dtucker Exp $ */
+/* $OpenBSD: sshkey.c,v 1.119 2021/07/23 03:37:52 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -3077,10 +3077,9 @@ sshkey_certify(struct sshkey *k, struct sshkey *ca, const char *alg,
 int
 sshkey_cert_check_authority(const struct sshkey *k,
     int want_host, int require_principal, int wildcard_pattern,
-    const char *name, const char **reason)
+    uint64_t verify_time, const char *name, const char **reason)
 {
 	u_int i, principal_matches;
-	time_t now = time(NULL);
 
 	if (reason == NULL)
 		return SSH_ERR_INVALID_ARGUMENT;
@@ -3099,16 +3098,11 @@ sshkey_cert_check_authority(const struct sshkey *k,
 			return SSH_ERR_KEY_CERT_INVALID;
 		}
 	}
-	if (now < 0) {
+	if (verify_time < k->cert->valid_after) {
-		/* yikes - system clock before epoch! */
 		*reason = "Certificate invalid: not yet valid";
 		return SSH_ERR_KEY_CERT_INVALID;
 	}
-	if ((u_int64_t)now < k->cert->valid_after) {
+	if (verify_time >= k->cert->valid_before) {
-		*reason = "Certificate invalid: not yet valid";
-		return SSH_ERR_KEY_CERT_INVALID;
-	}
-	if ((u_int64_t)now >= k->cert->valid_before) {
 		*reason = "Certificate invalid: expired";
 		return SSH_ERR_KEY_CERT_INVALID;
 	}
@@ -3140,6 +3134,22 @@ sshkey_cert_check_authority(const struct sshkey *k,
 	return 0;
 }
 
+int
+sshkey_cert_check_authority_now(const struct sshkey *k,
+    int want_host, int require_principal, int wildcard_pattern,
+    const char *name, const char **reason)
+{
+	time_t now;
+
+	if ((now = time(NULL)) < 0) {
+		/* yikes - system clock before epoch! */
+		*reason = "Certificate invalid: not yet valid";
+		return SSH_ERR_KEY_CERT_INVALID;
+	}
+	return sshkey_cert_check_authority(k, want_host, require_principal,
+	    wildcard_pattern, (uint64_t)now, name, reason);
+}
+
 int
 sshkey_cert_check_host(const struct sshkey *key, const char *host,
     int wildcard_principals, const char *ca_sign_algorithms,
@@ -3147,7 +3157,7 @@ sshkey_cert_check_host(const struct sshkey *key, const char *host,
 {
 	int r;
 
-	if ((r = sshkey_cert_check_authority(key, 1, 0, wildcard_principals,
+	if ((r = sshkey_cert_check_authority_now(key, 1, 0, wildcard_principals,
 	    host, reason)) != 0)
 		return r;
 	if (sshbuf_len(key->cert->critical) != 0) {

sshkey.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.h,v 1.49 2021/01/26 00:49:30 djm Exp $ */
+/* $OpenBSD: sshkey.h,v 1.50 2021/07/23 03:37:52 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -196,6 +196,8 @@ int	 sshkey_to_certified(struct sshkey *);
 int	 sshkey_drop_cert(struct sshkey *);
 int	 sshkey_cert_copy(const struct sshkey *, struct sshkey *);
 int	 sshkey_cert_check_authority(const struct sshkey *, int, int, int,
+    uint64_t, const char *, const char **);
+int	 sshkey_cert_check_authority_now(const struct sshkey *, int, int, int,
     const char *, const char **);
 int	 sshkey_cert_check_host(const struct sshkey *, const char *,
     int , const char *, const char **);

sshsig.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshsig.h,v 1.9 2020/08/31 00:17:41 djm Exp $ */
+/* $OpenBSD: sshsig.h,v 1.10 2021/07/23 03:37:52 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -86,7 +86,7 @@ int sshsig_dearmor(struct sshbuf *sig, struct sshbuf **out);
  * an allowed_keys file. Returns 0 on success.
  */
 int sshsig_check_allowed_keys(const char *path, const struct sshkey *sign_key,
-    const char *principal, const char *ns);
+    const char *principal, const char *ns, uint64_t verify_time);
 
 /* Parse zero or more allowed_keys signature options */
 struct sshsigopt *sshsigopt_parse(const char *opts,
@@ -102,6 +102,6 @@ int sshsig_get_pubkey(struct sshbuf *signature, struct sshkey **pubkey);
  * 0 on success.
  */
 int sshsig_find_principals(const char *path, const struct sshkey *sign_key,
-    char **principal);
+    uint64_t verify_time, char **principal);
 
 #endif /* SSHSIG_H */