upstream: when signing a challenge using a FIDO toke, perform the

hashing in the middleware layer rather than in ssh code. This allows
middlewares that call APIs that perform the hashing implicitly (including
Microsoft's AFAIK). ok markus@

OpenBSD-Commit-ID: c9fc8630aba26c75d5016884932f08a5a237f37d

4 files changed, 37 insertions, 18 deletions

diff --git a/PROTOCOL.u2f b/PROTOCOL.u2f
index 459958701..917e669cd 100644
--- a/PROTOCOL.u2f
+++ b/PROTOCOL.u2f
@@ -236,7 +236,7 @@ support for the common case of USB HID security keys internally.
 
 The middleware library need only expose a handful of functions:
 
-        #define SSH_SK_VERSION_MAJOR            0x00040000 /* API version */
+        #define SSH_SK_VERSION_MAJOR            0x00050000 /* API version */
         #define SSH_SK_VERSION_MAJOR_MASK       0xffff0000
 
         /* Flags */
diff --git a/sk-api.h b/sk-api.h
index 170fd4470..1ecaa3537 100644
--- a/sk-api.h
+++ b/sk-api.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sk-api.h,v 1.8 2020/01/25 23:13:09 djm Exp $ */
+/* $OpenBSD: sk-api.h,v 1.9 2020/04/28 04:02:29 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -71,7 +71,7 @@ struct sk_option {
         uint8_t required;
 };
 
-#define SSH_SK_VERSION_MAJOR            0x00040000 /* current API version */
+#define SSH_SK_VERSION_MAJOR            0x00050000 /* current API version */
 #define SSH_SK_VERSION_MAJOR_MASK       0xffff0000
 
 /* Return the version of the middleware API */
diff --git a/sk-usbhid.c b/sk-usbhid.c
index ad83054ad..db6c0057e 100644
--- a/sk-usbhid.c
+++ b/sk-usbhid.c
@@ -24,6 +24,7 @@
 #include <stdio.h>
 #include <stddef.h>
 #include <stdarg.h>
+#include <sha2.h>
 
 #ifdef WITH_OPENSSL
 #include <openssl/opensslv.h>
@@ -31,6 +32,7 @@
 #include <openssl/bn.h>
 #include <openssl/ec.h>
 #include <openssl/ecdsa.h>
+#include <openssl/evp.h>
 #endif /* WITH_OPENSSL */
 
 #include <fido.h>
@@ -710,8 +712,28 @@ check_sign_load_resident_options(struct sk_option **options, char **devicep)
         return 0;
 }
 
+/* Calculate SHA256(m) */
+static int
+sha256_mem(const void *m, size_t mlen, u_char *d, size_t dlen)
+{
+#ifdef WITH_OPENSSL
+        u_int mdlen;
+#endif
+
+        if (dlen != 32)
+                return -1;
+#ifdef WITH_OPENSSL
+        mdlen = dlen;
+        if (!EVP_Digest(m, mlen, d, &mdlen, EVP_sha256(), NULL))
+                return -1;
+#else
+        SHA256Data(m, mlen, d);
+#endif
+        return 0;
+}
+
 int
-sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
+sk_sign(uint32_t alg, const uint8_t *data, size_t datalen,
     const char *application,
     const uint8_t *key_handle, size_t key_handle_len,
     uint8_t flags, const char *pin, struct sk_option **options,
@@ -721,6 +743,7 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
         char *device = NULL;
         fido_dev_t *dev = NULL;
         struct sk_sign_response *response = NULL;
+        uint8_t message[32];
         int ret = SSH_SK_ERR_GENERAL;
         int r;
 
@@ -735,7 +758,12 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
         *sign_response = NULL;
         if (check_sign_load_resident_options(options, &device) != 0)
                 goto out; /* error already logged */
-        if ((dev = find_device(device, message, message_len,
+        /* hash data to be signed before it goes to the security key */
+        if ((r = sha256_mem(data, datalen, message, sizeof(message))) != 0) {
+                skdebug(__func__, "hash message failed");
+                goto out;
+        }
+        if ((dev = find_device(device, message, sizeof(message),
             application, key_handle, key_handle_len)) == NULL) {
                 skdebug(__func__, "couldn't find device for key handle");
                 goto out;
@@ -745,7 +773,7 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
                 goto out;
         }
         if ((r = fido_assert_set_clientdata_hash(assert, message,
-            message_len)) != FIDO_OK) {
+            sizeof(message))) != FIDO_OK) {
                 skdebug(__func__, "fido_assert_set_clientdata_hash: %s",
                     fido_strerr(r));
                 goto out;
@@ -783,6 +811,7 @@ sk_sign(uint32_t alg, const uint8_t *message, size_t message_len,
         response = NULL;
         ret = 0;
  out:
+        explicit_bzero(message, sizeof(message));
         free(device);
         if (response != NULL) {
                 free(response->sig_r);
diff --git a/ssh-sk.c b/ssh-sk.c
index 9aff7639a..1afb205f8 100644
--- a/ssh-sk.c
+++ b/ssh-sk.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-sk.c,v 1.29 2020/03/06 18:25:48 markus Exp $ */
+/* $OpenBSD: ssh-sk.c,v 1.30 2020/04/28 04:02:29 djm Exp $ */
 /*
  * Copyright (c) 2019 Google LLC
  *
@@ -615,7 +615,6 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
         int type, alg;
         struct sk_sign_response *resp = NULL;
         struct sshbuf *inner_sig = NULL, *sig = NULL;
-        uint8_t message[32];
         struct sk_option **opts = NULL;
 
         debug("%s: provider \"%s\", key %s, flags 0x%02x%s", __func__,
@@ -650,15 +649,7 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
                 goto out;
         }
 
-        /* hash data to be signed before it goes to the security key */
-        if ((r = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen,
-            message, sizeof(message))) != 0) {
-                error("%s: hash application failed: %s", __func__, ssh_err(r));
-                r = SSH_ERR_INTERNAL_ERROR;
-                goto out;
-        }
-        if ((r = skp->sk_sign(alg, message, sizeof(message),
-            key->sk_application,
+        if ((r = skp->sk_sign(alg, data, datalen, key->sk_application,
             sshbuf_ptr(key->sk_key_handle), sshbuf_len(key->sk_key_handle),
             key->sk_flags, pin, opts, &resp)) != 0) {
                 debug("%s: sk_sign failed with code %d", __func__, r);
@@ -707,7 +698,6 @@ sshsk_sign(const char *provider_path, struct sshkey *key,
         r = 0;
  out:
         sshsk_free_options(opts);
-        explicit_bzero(message, sizeof(message));
         sshsk_free(skp);
         sshsk_free_sign_response(resp);
         sshbuf_free(sig);