upstream: refactor ECDSA-SK verification a little ahead of adding

support for FIDO webauthn signature verification support; ok markus@

OpenBSD-Commit-ID: c9f478fd8e0c1bd17e511ce8694f010d8e32043e

1 files changed, 23 insertions, 21 deletions

diff --git a/ssh-ecdsa-sk.c b/ssh-ecdsa-sk.c
index 981d60d74..dcf605ba1 100644
--- a/ssh-ecdsa-sk.c
+++ b/ssh-ecdsa-sk.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-ecdsa-sk.c,v 1.5 2019/11/26 03:04:27 djm Exp $ */
+/* $OpenBSD: ssh-ecdsa-sk.c,v 1.6 2020/06/22 05:56:23 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2010 Damien Miller.  All rights reserved.
@@ -83,15 +83,22 @@ ssh_ecdsa_sk_verify(const struct sshkey *key,
         /* fetch signature */
         if ((b = sshbuf_from(signature, signaturelen)) == NULL)
                 return SSH_ERR_ALLOC_FAIL;
-        if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
-            sshbuf_froms(b, &sigbuf) != 0 ||
-            sshbuf_get_u8(b, &sig_flags) != 0 ||
-            sshbuf_get_u32(b, &sig_counter) != 0) {
+        if ((details = calloc(1, sizeof(*details))) == NULL) {
+                ret = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
+                ret = SSH_ERR_INVALID_FORMAT;
+                goto out;
+        }
+        if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) {
                 ret = SSH_ERR_INVALID_FORMAT;
                 goto out;
         }
-        if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) {
-                ret = SSH_ERR_KEY_TYPE_MISMATCH;
+        if (sshbuf_froms(b, &sigbuf) != 0 ||
+            sshbuf_get_u8(b, &sig_flags) != 0 ||
+            sshbuf_get_u32(b, &sig_counter) != 0) {
+                ret = SSH_ERR_INVALID_FORMAT;
                 goto out;
         }
         if (sshbuf_len(b) != 0) {
@@ -105,12 +112,8 @@ ssh_ecdsa_sk_verify(const struct sshkey *key,
                 ret = SSH_ERR_INVALID_FORMAT;
                 goto out;
         }
-        if ((sig = ECDSA_SIG_new()) == NULL) {
-                ret = SSH_ERR_ALLOC_FAIL;
-                goto out;
-        }
-        if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) {
-                ret = SSH_ERR_LIBCRYPTO_ERROR;
+        if (sshbuf_len(sigbuf) != 0) {
+                ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
                 goto out;
         }
 #ifdef DEBUG_SK
@@ -123,12 +126,15 @@ ssh_ecdsa_sk_verify(const struct sshkey *key,
         fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
             __func__, sig_flags, sig_counter);
 #endif
-        sig_r = sig_s = NULL; /* transferred */
-
-        if (sshbuf_len(sigbuf) != 0) {
-                ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
+        if ((sig = ECDSA_SIG_new()) == NULL) {
+                ret = SSH_ERR_ALLOC_FAIL;
                 goto out;
         }
+        if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) {
+                ret = SSH_ERR_LIBCRYPTO_ERROR;
+                goto out;
+        }
+        sig_r = sig_s = NULL; /* transferred */
 
         /* Reconstruct data that was supposedly signed */
         if ((original_signed = sshbuf_new()) == NULL) {
@@ -158,10 +164,6 @@ ssh_ecdsa_sk_verify(const struct sshkey *key,
         if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
             sighash, sizeof(sighash))) != 0)
                 goto out;
-        if ((details = calloc(1, sizeof(*details))) == NULL) {
-                ret = SSH_ERR_ALLOC_FAIL;
-                goto out;
-        }
         details->sk_counter = sig_counter;
         details->sk_flags = sig_flags;
 #ifdef DEBUG_SK