upstream: SK API and sk-helper error/PIN passing

Allow passing a PIN via the SK API (API major crank) and let the
ssh-sk-helper API follow.

Also enhance the ssh-sk-helper API to support passing back an error
code instead of a complete reply. Will be used to signal "wrong PIN",
etc.

feedback and ok markus@

OpenBSD-Commit-ID: a1bd6b0a2421646919a0c139b8183ad76d28fb71

1 files changed, 84 insertions, 22 deletions

diff --git a/ssh-sk-helper.c b/ssh-sk-helper.c
index ac528cfcf..590ff8501 100644
--- a/ssh-sk-helper.c
+++ b/ssh-sk-helper.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-sk-helper.c,v 1.5 2019/12/30 09:21:59 djm Exp $ */
+/* $OpenBSD: ssh-sk-helper.c,v 1.6 2019/12/30 09:23:28 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -50,6 +50,33 @@
 #ifdef ENABLE_SK
 extern char *__progname;
 
+static struct sshbuf *reply_error(int r, char *fmt, ...)
+    __attribute__((__format__ (printf, 2, 3)));
+
+static struct sshbuf *
+reply_error(int r, char *fmt, ...)
+{
+        char *msg;
+        va_list ap;
+        struct sshbuf *resp;
+
+        va_start(ap, fmt);
+        xvasprintf(&msg, fmt, ap);
+        va_end(ap);
+        error("%s: %s", __progname, msg);
+        free(msg);
+
+        if (r >= 0)
+                fatal("%s: invalid error code %d", __func__, r);
+
+        if ((resp = sshbuf_new()) == NULL)
+                fatal("%s: sshbuf_new failed", __progname);
+        if (sshbuf_put_u32(resp, SSH_SK_HELPER_ERROR) != 0 ||
+            sshbuf_put_u32(resp, (u_int)-r) != 0)
+                fatal("%s: buffer error", __progname);
+        return resp;
+}
+
 static struct sshbuf *
 process_sign(struct sshbuf *req)
 {
@@ -60,13 +87,14 @@ process_sign(struct sshbuf *req)
         const u_char *message;
         u_char *sig;
         size_t msglen, siglen;
-        char *provider;
+        char *provider, *pin;
 
         if ((r = sshbuf_froms(req, &kbuf)) != 0 ||
             (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
             (r = sshbuf_get_string_direct(req, &message, &msglen)) != 0 ||
             (r = sshbuf_get_cstring(req, NULL, NULL)) != 0 || /* alg */
-            (r = sshbuf_get_u32(req, &compat)) != 0)
+            (r = sshbuf_get_u32(req, &compat)) != 0 ||
+            (r = sshbuf_get_cstring(req, &pin, NULL)) != 0)
                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
         if (sshbuf_len(req) != 0)
                 fatal("%s: trailing data in request", __progname);
@@ -80,19 +108,28 @@ process_sign(struct sshbuf *req)
             "msg len %zu, compat 0x%lx", __progname, sshkey_type(key),
             provider, msglen, (u_long)compat);
 
+        if (*pin == 0) {
+                free(pin);
+                pin = NULL;
+        }
+
         if ((r = sshsk_sign(provider, key, &sig, &siglen,
-            message, msglen, compat)) != 0)
-                fatal("Signing failed: %s", ssh_err(r));
+            message, msglen, compat, pin)) != 0) {
+                resp = reply_error(r, "Signing failed: %s", ssh_err(r));
+                goto out;
+        }
 
         if ((resp = sshbuf_new()) == NULL)
                 fatal("%s: sshbuf_new failed", __progname);
 
-        if ((r = sshbuf_put_string(resp, sig, siglen)) != 0)
+        if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_SIGN)) != 0 ||
+            (r = sshbuf_put_string(resp, sig, siglen)) != 0)
                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
-
+ out:
         sshbuf_free(kbuf);
         free(provider);
-
+        if (pin != NULL)
+                freezero(pin, strlen(pin));
         return resp;
 }
 
@@ -101,14 +138,12 @@ process_enroll(struct sshbuf *req)
 {
         int r;
         u_int type;
-        char *provider;
-        char *application;
+        char *provider, *application, *pin;
         uint8_t flags;
         struct sshbuf *challenge, *attest, *kbuf, *resp;
         struct sshkey *key;
 
-        if ((resp = sshbuf_new()) == NULL ||
-            (attest = sshbuf_new()) == NULL ||
+        if ((attest = sshbuf_new()) == NULL ||
             (kbuf = sshbuf_new()) == NULL)
                 fatal("%s: sshbuf_new failed", __progname);
 
@@ -116,6 +151,7 @@ process_enroll(struct sshbuf *req)
             (r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
             (r = sshbuf_get_cstring(req, &application, NULL)) != 0 ||
             (r = sshbuf_get_u8(req, &flags)) != 0 ||
+            (r = sshbuf_get_cstring(req, &pin, NULL)) != 0 ||
             (r = sshbuf_froms(req, &challenge)) != 0)
                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
         if (sshbuf_len(req) != 0)
@@ -127,23 +163,35 @@ process_enroll(struct sshbuf *req)
                 sshbuf_free(challenge);
                 challenge = NULL;
         }
+        if (*pin == 0) {
+                free(pin);
+                pin = NULL;
+        }
 
-        if ((r = sshsk_enroll((int)type, provider, application, flags,
-            challenge, &key, attest)) != 0)
-                fatal("%s: sshsk_enroll failed: %s", __progname, ssh_err(r));
+        if ((r = sshsk_enroll((int)type, provider, application, flags, pin,
+            challenge, &key, attest)) != 0) {
+                resp = reply_error(r, "Enrollment failed: %s", ssh_err(r));
+                goto out;
+        }
 
+        if ((resp = sshbuf_new()) == NULL)
+                fatal("%s: sshbuf_new failed", __progname);
         if ((r = sshkey_private_serialize(key, kbuf)) != 0)
                 fatal("%s: serialize private key: %s", __progname, ssh_err(r));
-        if ((r = sshbuf_put_stringb(resp, kbuf)) != 0 ||
+        if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_ENROLL)) != 0 ||
+            (r = sshbuf_put_stringb(resp, kbuf)) != 0 ||
             (r = sshbuf_put_stringb(resp, attest)) != 0)
                 fatal("%s: buffer error: %s", __progname, ssh_err(r));
 
+ out:
         sshkey_free(key);
         sshbuf_free(kbuf);
         sshbuf_free(attest);
         sshbuf_free(challenge);
         free(provider);
         free(application);
+        if (pin != NULL)
+                freezero(pin, strlen(pin));
 
         return resp;
 }
@@ -157,8 +205,7 @@ process_load_resident(struct sshbuf *req)
         struct sshkey **keys = NULL;
         size_t nkeys = 0, i;
 
-        if ((resp = sshbuf_new()) == NULL ||
-            (kbuf = sshbuf_new()) == NULL)
+        if ((kbuf = sshbuf_new()) == NULL)
                 fatal("%s: sshbuf_new failed", __progname);
 
         if ((r = sshbuf_get_cstring(req, &provider, NULL)) != 0 ||
@@ -167,9 +214,22 @@ process_load_resident(struct sshbuf *req)
         if (sshbuf_len(req) != 0)
                 fatal("%s: trailing data in request", __progname);
 
-        if ((r = sshsk_load_resident(provider, pin, &keys, &nkeys)) != 0)
-                fatal("%s: sshsk_load_resident failed: %s",
-                    __progname, ssh_err(r));
+        if (*pin == 0) {
+                free(pin);
+                pin = NULL;
+        }
+
+        if ((r = sshsk_load_resident(provider, pin, &keys, &nkeys)) != 0) {
+                resp = reply_error(r, " sshsk_load_resident failed: %s",
+                    ssh_err(r));
+                goto out;
+        }
+
+        if ((resp = sshbuf_new()) == NULL)
+                fatal("%s: sshbuf_new failed", __progname);
+
+        if ((r = sshbuf_put_u32(resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
+                fatal("%s: buffer error: %s", __progname, ssh_err(r));
 
         for (i = 0; i < nkeys; i++) {
                 debug("%s: key %zu %s %s", __func__, i,
@@ -183,12 +243,14 @@ process_load_resident(struct sshbuf *req)
                         fatal("%s: buffer error: %s", __progname, ssh_err(r));
         }
 
+ out:
         for (i = 0; i < nkeys; i++)
                 sshkey_free(keys[i]);
         free(keys);
         sshbuf_free(kbuf);
         free(provider);
-        freezero(pin, strlen(pin));
+        if (pin != NULL)
+                freezero(pin, strlen(pin));
         return resp;
 }