upstream: resident keys support in SK API

Adds a sk_load_resident_keys() function to the security key
API that accepts a security key provider and a PIN and returns
a list of keys.

Implement support for this in the usbhid middleware.

feedback and ok markus@

OpenBSD-Commit-ID: 67e984e4e87f4999ce447a6178c4249a9174eff0

1 files changed, 112 insertions, 4 deletions

diff --git a/ssh-sk.c b/ssh-sk.c
index 01927669e..d48f34e30 100644
--- a/ssh-sk.c
+++ b/ssh-sk.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-sk.c,v 1.19 2019/12/30 09:20:36 djm Exp $ */
+/* $OpenBSD: ssh-sk.c,v 1.20 2019/12/30 09:21:16 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -60,6 +60,10 @@ struct sshsk_provider {
             const char *application,
             const uint8_t *key_handle, size_t key_handle_len,
             uint8_t flags, struct sk_sign_response **sign_response);
+
+        /* Enumerate resident keys */
+        int (*sk_load_resident_keys)(const char *pin,
+            struct sk_resident_key ***rks, size_t *nrks);
 };
 
 /* Built-in version */
@@ -70,6 +74,8 @@ int ssh_sk_sign(int alg, const uint8_t *message, size_t message_len,
     const char *application,
     const uint8_t *key_handle, size_t key_handle_len,
     uint8_t flags, struct sk_sign_response **sign_response);
+int ssh_sk_load_resident_keys(const char *pin,
+    struct sk_resident_key ***rks, size_t *nrks);
 
 static void
 sshsk_free(struct sshsk_provider *p)
@@ -101,6 +107,7 @@ sshsk_open(const char *path)
 #ifdef ENABLE_SK_INTERNAL
                 ret->sk_enroll = ssh_sk_enroll;
                 ret->sk_sign = ssh_sk_sign;
+                ret->sk_load_resident_keys = ssh_sk_load_resident_keys;
 #else
                 error("internal security key support not enabled");
 #endif
@@ -136,6 +143,12 @@ sshsk_open(const char *path)
                     path, dlerror());
                 goto fail;
         }
+        if ((ret->sk_load_resident_keys = dlsym(ret->dlhandle,
+            "sk_load_resident_keys")) == NULL) {
+                error("Security key provider %s dlsym(sk_load_resident_keys) "
+                    "failed: %s", path, dlerror());
+                goto fail;
+        }
         /* success */
         return ret;
 fail:
@@ -264,9 +277,7 @@ sshsk_key_from_response(int alg, const char *application, uint8_t flags,
         *keyp = NULL;
 
         /* Check response validity */
-        if (resp->public_key == NULL || resp->key_handle == NULL ||
-            resp->signature == NULL ||
-            (resp->attestation_cert == NULL && resp->attestation_cert_len != 0)) {
+        if (resp->public_key == NULL || resp->key_handle == NULL) {
                 error("%s: sk_enroll response invalid", __func__);
                 r = SSH_ERR_INVALID_FORMAT;
                 goto out;
@@ -595,4 +606,101 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
         sshbuf_free(inner_sig);
         return r;
 }
+
+static void
+sshsk_free_sk_resident_keys(struct sk_resident_key **rks, size_t nrks)
+{
+        size_t i;
+
+        if (nrks == 0 || rks == NULL)
+                return;
+        for (i = 0; i < nrks; i++) {
+                free(rks[i]->application);
+                freezero(rks[i]->key.key_handle, rks[i]->key.key_handle_len);
+                freezero(rks[i]->key.public_key, rks[i]->key.public_key_len);
+                freezero(rks[i]->key.signature, rks[i]->key.signature_len);
+                freezero(rks[i]->key.attestation_cert,
+                    rks[i]->key.attestation_cert_len);
+                freezero(rks[i], sizeof(**rks));
+        }
+        free(rks);
+}
+
+int
+sshsk_load_resident(const char *provider_path, const char *pin,
+    struct sshkey ***keysp, size_t *nkeysp)
+{
+        struct sshsk_provider *skp = NULL;
+        int r = SSH_ERR_INTERNAL_ERROR;
+        struct sk_resident_key **rks = NULL;
+        size_t i, nrks = 0, nkeys = 0;
+        struct sshkey *key = NULL, **keys = NULL, **tmp;
+        uint8_t flags;
+
+        debug("%s: provider \"%s\"%s", __func__, provider_path,
+            (pin != NULL && *pin != '\0') ? ", have-pin": "");
+
+        if (keysp == NULL || nkeysp == NULL)
+                return SSH_ERR_INVALID_ARGUMENT;
+        *keysp = NULL;
+        *nkeysp = 0;
+
+        if ((skp = sshsk_open(provider_path)) == NULL) {
+                r = SSH_ERR_INVALID_FORMAT; /* XXX sshsk_open return code? */
+                goto out;
+        }
+        if ((r = skp->sk_load_resident_keys(pin, &rks, &nrks)) != 0) {
+                error("Security key provider %s returned failure %d",
+                    provider_path, r);
+                r = SSH_ERR_INVALID_FORMAT; /* XXX error codes in API? */
+                goto out;
+        }
+        for (i = 0; i < nrks; i++) {
+                debug3("%s: rk %zu: slot = %zu, alg = %d, application = \"%s\"",
+                    __func__, i, rks[i]->slot, rks[i]->alg,
+                    rks[i]->application);
+                /* XXX need better filter here */
+                if (strncmp(rks[i]->application, "ssh:", 4) != 0)
+                        continue;
+                switch (rks[i]->alg) {
+                case SSH_SK_ECDSA:
+                case SSH_SK_ED25519:
+                        break;
+                default:
+                        continue;
+                }
+                /* XXX where to get flags? */
+                flags = SSH_SK_USER_PRESENCE_REQD|SSH_SK_RESIDENT_KEY;
+                if ((r = sshsk_key_from_response(rks[i]->alg,
+                    rks[i]->application, flags, &rks[i]->key, &key)) != 0)
+                        goto out;
+                if ((tmp = recallocarray(keys, nkeys, nkeys + 1,
+                    sizeof(*tmp))) == NULL) {
+                        error("%s: recallocarray failed", __func__);
+                        r = SSH_ERR_ALLOC_FAIL;
+                        goto out;
+                }
+                keys = tmp;
+                keys[nkeys++] = key;
+                key = NULL;
+                /* XXX synthesise comment */
+        }
+        /* success */
+        *keysp = keys;
+        *nkeysp = nkeys;
+        keys = NULL;
+        nkeys = 0;
+        r = 0;
+ out:
+        sshsk_free(skp);
+        sshsk_free_sk_resident_keys(rks, nrks);
+        sshkey_free(key);
+        if (nkeys != 0) {
+                for (i = 0; i < nkeys; i++)
+                        sshkey_free(keys[i]);
+                free(keys);
+        }
+        return r;
+}
+
 #endif /* ENABLE_SK */