GSSAPI key exchange support

This patch has been rejected upstream: "None of the OpenSSH developers are
in favour of adding this, and this situation has not changed for several
years.  This is not a slight on Simon's patch, which is of fine quality, but
just that a) we don't trust GSSAPI implementations that much and b) we don't
like adding new KEX since they are pre-auth attack surface.  This one is
particularly scary, since it requires hooks out to typically root-owned
system resources."

However, quite a lot of people rely on this in Debian, and it's better to
have it merged into the main openssh package rather than having separate
-krb5 packages (as we used to have).  It seems to have a generally good
security history.

Author: Simon Wilkinson <simon@sxw.org.uk>
Author: Colin Watson <cjwatson@debian.org>
Author: Jakub Jelen <jjelen@redhat.com>
Origin: other, https://github.com/openssh-gsskex/openssh-gsskex/pull/23
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2023-01-02

Patch-Name: gssapi.patch

1 files changed, 29 insertions, 0 deletions

diff --git a/kex.h b/kex.h
index c35329501..240dca89d 100644
--- a/kex.h
+++ b/kex.h
@@ -102,6 +102,15 @@ enum kex_exchange {
 	KEX_ECDH_SHA2,
 	KEX_C25519_SHA256,
 	KEX_KEM_SNTRUP761X25519_SHA512,
+#ifdef GSSAPI
+	KEX_GSS_GRP1_SHA1,
+	KEX_GSS_GRP14_SHA1,
+	KEX_GSS_GRP14_SHA256,
+	KEX_GSS_GRP16_SHA512,
+	KEX_GSS_GEX_SHA1,
+	KEX_GSS_NISTP256_SHA256,
+	KEX_GSS_C25519_SHA256,
+#endif
 	KEX_MAX
 };
 
@@ -159,6 +168,12 @@ struct kex {
 	u_int	flags;
 	int	hash_alg;
 	int	ec_nid;
+#ifdef GSSAPI
+	int	gss_deleg_creds;
+	int	gss_trust_dns;
+	char    *gss_host;
+	char	*gss_client;
+#endif
 	char	*failed_choice;
 	int	(*verify_host_key)(struct sshkey *, struct ssh *);
 	struct sshkey *(*load_host_public_key)(int, int, struct ssh *);
@@ -180,8 +195,10 @@ struct kex {
 
 int	 kex_names_valid(const char *);
 char	*kex_alg_list(char);
+char	*kex_gss_alg_list(char);
 char	*kex_names_cat(const char *, const char *);
 int	 kex_assemble_names(char **, const char *, const char *);
+int	 kex_gss_names_valid(const char *);
 
 int	 kex_exchange_identification(struct ssh *, int, const char *);
 
@@ -209,6 +226,12 @@ int	 kexgex_client(struct ssh *);
 int	 kexgex_server(struct ssh *);
 int	 kex_gen_client(struct ssh *);
 int	 kex_gen_server(struct ssh *);
+#if defined(GSSAPI) && defined(WITH_OPENSSL)
+int	 kexgssgex_client(struct ssh *);
+int	 kexgssgex_server(struct ssh *);
+int	 kexgss_client(struct ssh *);
+int	 kexgss_server(struct ssh *);
+#endif
 
 int	 kex_dh_keypair(struct kex *);
 int	 kex_dh_enc(struct kex *, const struct sshbuf *, struct sshbuf **,
@@ -241,6 +264,12 @@ int	 kexgex_hash(int, const struct sshbuf *, const struct sshbuf *,
     const BIGNUM *, const u_char *, size_t,
     u_char *, size_t *);
 
+int	 kex_gen_hash(int hash_alg, const struct sshbuf *client_version,
+    const struct sshbuf *server_version, const struct sshbuf *client_kexinit,
+    const struct sshbuf *server_kexinit, const struct sshbuf *server_host_key_blob,
+    const struct sshbuf *client_pub, const struct sshbuf *server_pub,
+    const struct sshbuf *shared_secret, u_char *hash, size_t *hashlen);
+
 void	kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
 	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
 	__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)));