If a signature operation on a FIDO key fails with a "incorrect PIN"

reason and no PIN was initially requested from the user, then request
a PIN and retry the operation.

This smoothes over a few corner cases including FIDO devices that
require PINs for all hosted credentials, biometric FIDO devices that
fall back to requiring PIN when reading the biometric failed, devices
that don't implement reading credProtect status for downloaded keys
and probably a few more cases that I haven't though of yet.

ok dtucker@

1 files changed, 12 insertions, 3 deletions

diff --git a/usr.bin/ssh/sshconnect2.c b/usr.bin/ssh/sshconnect2.c
index b568b087d8d..87011733011 100644
--- a/usr.bin/ssh/sshconnect2.c
+++ b/usr.bin/ssh/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.340 2020/12/29 00:59:15 djm Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.341 2021/01/08 02:57:24 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -1214,7 +1214,7 @@ identity_sign(struct identity *id, u_char **sigp, size_t *lenp,
     const u_char *data, size_t datalen, u_int compat, const char *alg)
 {
 	struct sshkey *sign_key = NULL, *prv = NULL;
-	int r = SSH_ERR_INTERNAL_ERROR;
+	int retried = 0, r = SSH_ERR_INTERNAL_ERROR;
 	struct notifier_ctx *notifier = NULL;
 	char *fp = NULL, *pin = NULL, *prompt = NULL;
 
@@ -1248,6 +1248,7 @@ identity_sign(struct identity *id, u_char **sigp, size_t *lenp,
 		if (sshkey_is_sk(sign_key)) {
 			if ((sign_key->sk_flags &
 			    SSH_SK_USER_VERIFICATION_REQD)) {
+ retry_pin:
 				xasprintf(&prompt, "Enter PIN for %s key %s: ",
 				    sshkey_type(sign_key), id->filename);
 				pin = read_passphrase(prompt, 0);
@@ -1268,8 +1269,16 @@ identity_sign(struct identity *id, u_char **sigp, size_t *lenp,
 	if ((r = sshkey_sign(sign_key, sigp, lenp, data, datalen,
 	    alg, options.sk_provider, pin, compat)) != 0) {
 		debug_fr(r, "sshkey_sign");
+		if (pin == NULL && !retried && sshkey_is_sk(sign_key) &&
+		    r == SSH_ERR_KEY_WRONG_PASSPHRASE) {
+			notify_complete(notifier, NULL);
+			notifier = NULL;
+			retried = 1;
+			goto retry_pin;
+		}
 		goto out;
 	}
+
 	/*
 	 * PKCS#11 tokens may not support all signature algorithms,
 	 * so check what we get back.
@@ -1284,7 +1293,7 @@ identity_sign(struct identity *id, u_char **sigp, size_t *lenp,
 	free(prompt);
 	if (pin != NULL)
 		freezero(pin, strlen(pin));
-	notify_complete(notifier, "User presence confirmed");
+	notify_complete(notifier, r == 0 ? "User presence confirmed" : NULL);
 	sshkey_free(prv);
 	return r;
 }