upstream: Request PIN ahead of time for certain FIDO actions

When we know that a particular action will require a PIN, such as
downloading resident keys or generating a verify-required key, request
the PIN before attempting it.

joint work with Pedro Martelletto; ok markus@

OpenBSD-Commit-ID: 863182d38ef075bad1f7d20ca485752a05edb727

2 files changed, 23 insertions, 19 deletions

diff --git a/ssh-keygen.1 b/ssh-keygen.1
index 7e0558fe1..e18fcde01 100644
--- a/ssh-keygen.1
+++ b/ssh-keygen.1
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: ssh-keygen.1,v 1.206 2020/08/27 01:06:18 djm Exp $
+.\"     $OpenBSD: ssh-keygen.1,v 1.207 2020/08/27 01:08:45 djm Exp $
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -382,6 +382,8 @@ The default import format is
 Download resident keys from a FIDO authenticator.
 Public and private key files will be written to the current directory for
 each downloaded key.
+If multiple FIDO authenticators are attached, keys will be downloaded from
+the first touched authenticator.
 .It Fl k
 Generate a KRL file.
 In this mode,
diff --git a/ssh-keygen.c b/ssh-keygen.c
index 1d6234c1c..664724276 100644
--- a/ssh-keygen.c
+++ b/ssh-keygen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.417 2020/08/27 01:07:51 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.418 2020/08/27 01:08:45 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -2984,20 +2984,17 @@ do_download_sk(const char *skprovider, const char *device)
         if (skprovider == NULL)
                 fatal("Cannot download keys without provider");
 
-        for (i = 0; i < 2; i++) {
-                if (i == 1) {
-                        pin = read_passphrase("Enter PIN for authenticator: ",
-                            RP_ALLOW_STDIN);
-                }
-                if ((r = sshsk_load_resident(skprovider, device, pin,
-                    &keys, &nkeys)) != 0) {
-                        if (i == 0 && r == SSH_ERR_KEY_WRONG_PASSPHRASE)
-                                continue;
-                        if (pin != NULL)
-                                freezero(pin, strlen(pin));
-                        error("Unable to load resident keys: %s", ssh_err(r));
-                        return -1;
-                }
+        pin = read_passphrase("Enter PIN for authenticator: ", RP_ALLOW_STDIN);
+        if (!quiet) {
+                printf("You may need to touch your authenticator "
+                    "to authorize key download.\n");
+        }
+        if ((r = sshsk_load_resident(skprovider, device, pin,
+            &keys, &nkeys)) != 0) {
+                if (pin != NULL)
+                        freezero(pin, strlen(pin));
+                error("Unable to load resident keys: %s", ssh_err(r));
+                return -1;
         }
         if (nkeys == 0)
                 logit("No keys to download");
@@ -3609,9 +3606,15 @@ main(int argc, char **argv)
                         printf("You may need to touch your authenticator "
                             "to authorize key generation.\n");
                 }
-                passphrase = NULL;
                 if ((attest = sshbuf_new()) == NULL)
                         fatal("sshbuf_new failed");
+                if ((sk_flags &
+                    (SSH_SK_USER_VERIFICATION_REQD|SSH_SK_RESIDENT_KEY))) {
+                        passphrase = read_passphrase("Enter PIN for "
+                            "authenticator: ", RP_ALLOW_STDIN);
+                } else {
+                        passphrase = NULL;
+                }
                 for (i = 0 ; ; i++) {
                         fflush(stdout);
                         r = sshsk_enroll(type, sk_provider, sk_device,
@@ -3622,9 +3625,8 @@ main(int argc, char **argv)
                                 break;
                         if (r != SSH_ERR_KEY_WRONG_PASSPHRASE)
                                 fatal("Key enrollment failed: %s", ssh_err(r));
-                        else if (i > 0)
+                        else if (passphrase != NULL) {
                                 error("PIN incorrect");
-                        if (passphrase != NULL) {
                                 freezero(passphrase, strlen(passphrase));
                                 passphrase = NULL;
                         }