upstream: Enable credProtect extension when generating a resident

key.

The FIDO 2.1 Client to Authenticator Protocol introduced a "credProtect"
feature to better protect resident keys. This option allows (amone other
possibilities) requiring a PIN prior to all operations that may retrieve
the key handle.

Patch by Pedro Martelletto; ok djm and markus

OpenBSD-Commit-ID: 013bc06a577dcaa66be3913b7f183eb8cad87e73

1 files changed, 57 insertions, 0 deletions

diff --git a/sk-usbhid.c b/sk-usbhid.c
index 8097cc7f4..4d64550c9 100644
--- a/sk-usbhid.c
+++ b/sk-usbhid.c
@@ -449,6 +449,43 @@ check_enroll_options(struct sk_option **options, char **devicep,
         return 0;
 }
 
+static int
+check_sk_extensions(fido_dev_t *dev, const char *ext, int *ret)
+{
+        fido_cbor_info_t *info;
+        char * const *ptr;
+        size_t len;
+        int r;
+
+        *ret = 0;
+
+        if (!fido_dev_is_fido2(dev)) {
+                skdebug(__func__, "device is not fido2");
+                return 0;
+        }
+        if ((info = fido_cbor_info_new()) == NULL) {
+                skdebug(__func__, "fido_cbor_info_new failed");
+                return -1;
+        }
+        if ((r = fido_dev_get_cbor_info(dev, info)) != FIDO_OK) {
+                skdebug(__func__, "fido_dev_get_cbor_info: %s", fido_strerr(r));
+                fido_cbor_info_free(&info);
+                return -1;
+        }
+        ptr = fido_cbor_info_extensions_ptr(info);
+        len = fido_cbor_info_extensions_len(info);
+        for (size_t i = 0; i < len; i++) {
+                if (!strcmp(ptr[i], ext)) {
+                        *ret = 1;
+                        break;
+                }
+        }
+        fido_cbor_info_free(&info);
+        skdebug(__func__, "extension %s %s", ext, *ret ? "present" : "absent");
+
+        return 0;
+}
+
 int
 sk_enroll(uint32_t alg, const uint8_t *challenge, size_t challenge_len,
     const char *application, uint8_t flags, const char *pin,
@@ -460,6 +497,7 @@ sk_enroll(uint32_t alg, const uint8_t *challenge, size_t challenge_len,
         uint8_t user_id[32];
         struct sk_enroll_response *response = NULL;
         size_t len;
+        int credprot;
         int cose_alg;
         int ret = SSH_SK_ERR_GENERAL;
         int r;
@@ -532,6 +570,25 @@ sk_enroll(uint32_t alg, const uint8_t *challenge, size_t challenge_len,
                 skdebug(__func__, "fido_dev_open: %s", fido_strerr(r));
                 goto out;
         }
+        if ((flags & SSH_SK_RESIDENT_KEY) != 0) {
+                if (check_sk_extensions(dev, "credProtect", &credprot) < 0) {
+                        skdebug(__func__, "check_sk_extensions failed");
+                        goto out;
+                }
+                if (credprot == 0) {
+                        skdebug(__func__, "refusing to create unprotected "
+                            "resident key");
+                        ret = SSH_SK_ERR_UNSUPPORTED;
+                        goto out;
+                }
+                if ((r = fido_cred_set_prot(cred,
+                    FIDO_CRED_PROT_UV_OPTIONAL_WITH_ID)) != FIDO_OK) {
+                        skdebug(__func__, "fido_cred_set_prot: %s",
+                            fido_strerr(r));
+                        ret = fidoerr_to_skerr(r);
+                        goto out;
+                }
+        }
         if ((r = fido_dev_make_cred(dev, cred, pin)) != FIDO_OK) {
                 skdebug(__func__, "fido_dev_make_cred: %s", fido_strerr(r));
                 ret = fidoerr_to_skerr(r);