upstream: add sshkey_check_cert_sigtype() that checks a

cert->signature_type against a supplied whitelist; ok markus

OpenBSD-Commit-ID: caadb8073292ed7a9535e5adc067d11d356d9302

2 files changed, 24 insertions, 2 deletions

diff --git a/sshkey.c b/sshkey.c
index b467571fd..50ebdc256 100644
--- a/sshkey.c
+++ b/sshkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.67 2018/09/12 01:31:30 djm Exp $ */
+/* $OpenBSD: sshkey.c,v 1.68 2018/09/12 01:32:54 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -2261,6 +2261,27 @@ get_sigtype(const u_char *sig, size_t siglen, char **sigtypep)
 }
 
 /*
+ *
+ * Checks whether a certificate's signature type is allowed.
+ * Returns 0 (success) if the certificate signature type appears in the
+ * "allowed" pattern-list, or the key is not a certificate to begin with.
+ * Otherwise returns a ssherr.h code.
+ */
+int
+sshkey_check_cert_sigtype(const struct sshkey *key, const char *allowed)
+{
+        if (key == NULL || allowed == NULL)
+                return SSH_ERR_INVALID_ARGUMENT;
+        if (!sshkey_type_is_cert(key->type))
+                return 0;
+        if (key->cert == NULL || key->cert->signature_type == NULL)
+                return SSH_ERR_INVALID_ARGUMENT;
+        if (match_pattern_list(key->cert->signature_type, allowed, 0) != 1)
+                return SSH_ERR_SIGN_ALG_UNSUPPORTED;
+        return 0;
+}
+
+/*
  * Returns the expected signature algorithm for a given public key algorithm.
  */
 const char *
diff --git a/sshkey.h b/sshkey.h
index b8f279a60..5a22a66f5 100644
--- a/sshkey.h
+++ b/sshkey.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.h,v 1.27 2018/09/12 01:31:30 djm Exp $ */
+/* $OpenBSD: sshkey.h,v 1.28 2018/09/12 01:32:54 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -158,6 +158,7 @@ int	 sshkey_cert_check_authority(const struct sshkey *, int, int,
     const char *, const char **);
 size_t   sshkey_format_cert_validity(const struct sshkey_cert *,
     char *, size_t) __attribute__((__bounded__(__string__, 2, 3)));
+int      sshkey_check_cert_sigtype(const struct sshkey *, const char *);
 
 int      sshkey_certify(struct sshkey *, struct sshkey *, const char *);
 /* Variant allowing use of a custom signature function (e.g. for ssh-agent) */