upstream: when writing an attestation blob for a FIDO key, record all

the data needed to verify the attestation. Previously we were missing the
"authenticator data" that is included in the signature.

spotted by Ian Haken
feedback Pedro Martelletto and Ian Haken; ok markus@

OpenBSD-Commit-ID: 8439896e63792b2db99c6065dd9a45eabbdb7e0a

1 files changed, 30 insertions, 14 deletions

diff --git a/ssh-sk.c b/ssh-sk.c
index 89478aff0..1455df635 100644
--- a/ssh-sk.c
+++ b/ssh-sk.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-sk.c,v 1.31 2020/08/27 01:08:19 djm Exp $ */
+/* $OpenBSD: ssh-sk.c,v 1.32 2020/09/09 03:08:02 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -174,6 +174,7 @@ sshsk_free_enroll_response(struct sk_enroll_response *r)
         freezero(r->public_key, r->public_key_len);
         freezero(r->signature, r->signature_len);
         freezero(r->attestation_cert, r->attestation_cert_len);
+        freezero(r->authdata, r->authdata_len);
         freezero(r, sizeof(*r));
 }
 
@@ -419,6 +420,31 @@ make_options(const char *device, const char *user_id,
         return ret;
 }
 
+
+static int
+fill_attestation_blob(const struct sk_enroll_response *resp,
+    struct sshbuf *attest)
+{
+        int r;
+
+        if (attest == NULL)
+                return 0; /* nothing to do */
+        if ((r = sshbuf_put_cstring(attest, "ssh-sk-attest-v01")) != 0 ||
+            (r = sshbuf_put_string(attest,
+            resp->attestation_cert, resp->attestation_cert_len)) != 0 ||
+            (r = sshbuf_put_string(attest,
+            resp->signature, resp->signature_len)) != 0 ||
+            (r = sshbuf_put_string(attest,
+            resp->authdata, resp->authdata_len)) != 0 ||
+            (r = sshbuf_put_u32(attest, 0)) != 0 || /* resvd flags */
+            (r = sshbuf_put_string(attest, NULL, 0)) != 0 /* resvd */) {
+                error("%s: buffer error: %s", __func__, ssh_err(r));
+                return r;
+        }
+        /* success */
+        return 0;
+}
+
 int
 sshsk_enroll(int type, const char *provider_path, const char *device,
     const char *application, const char *userid, uint8_t flags,
@@ -506,19 +532,9 @@ sshsk_enroll(int type, const char *provider_path, const char *device,
                 goto out;
 
         /* Optionally fill in the attestation information */
-        if (attest != NULL) {
-                if ((r = sshbuf_put_cstring(attest,
-                    "ssh-sk-attest-v00")) != 0 ||
-                    (r = sshbuf_put_string(attest,
-                    resp->attestation_cert, resp->attestation_cert_len)) != 0 ||
-                    (r = sshbuf_put_string(attest,
-                    resp->signature, resp->signature_len)) != 0 ||
-                    (r = sshbuf_put_u32(attest, 0)) != 0 || /* resvd flags */
-                    (r = sshbuf_put_string(attest, NULL, 0)) != 0 /* resvd */) {
-                        error("%s: buffer error: %s", __func__, ssh_err(r));
-                        goto out;
-                }
-        }
+        if ((r = fill_attestation_blob(resp, attest)) != 0)
+                goto out;
+
         /* success */
         *keyp = key;
         key = NULL; /* transferred */