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.

Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2017-01-16

Patch-Name: gssapi.patch

1 files changed, 19 insertions, 0 deletions

diff --git a/kex.c b/kex.c
index cf4ac0dc5..556a32e98 100644
--- a/kex.c
+++ b/kex.c
@@ -54,6 +54,10 @@
 #include "sshbuf.h"
 #include "digest.h"
 
+#ifdef GSSAPI
+#include "ssh-gss.h"
+#endif
+
 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 # if defined(HAVE_EVP_SHA256)
 # define evp_ssh_sha256 EVP_sha256
@@ -113,6 +117,14 @@ static const struct kexalg kexalgs[] = {
 #endif /* HAVE_EVP_SHA256 || !WITH_OPENSSL */
         { NULL, -1, -1, -1},
 };
+static const struct kexalg kexalg_prefixes[] = {
+#ifdef GSSAPI
+        { KEX_GSS_GEX_SHA1_ID, KEX_GSS_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
+        { KEX_GSS_GRP1_SHA1_ID, KEX_GSS_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
+        { KEX_GSS_GRP14_SHA1_ID, KEX_GSS_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
+#endif
+        { NULL, -1, -1, -1 },
+};
 
 char *
 kex_alg_list(char sep)
@@ -145,6 +157,10 @@ kex_alg_by_name(const char *name)
                 if (strcmp(k->name, name) == 0)
                         return k;
         }
+        for (k = kexalg_prefixes; k->name != NULL; k++) {
+                if (strncmp(k->name, name, strlen(k->name)) == 0)
+                        return k;
+        }
         return NULL;
 }
 
@@ -605,6 +621,9 @@ kex_free(struct kex *kex)
         sshbuf_free(kex->peer);
         sshbuf_free(kex->my);
         free(kex->session_id);
+#ifdef GSSAPI
+        free(kex->gss_host);
+#endif /* GSSAPI */
         free(kex->client_version_string);
         free(kex->server_version_string);
         free(kex->failed_choice);