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

support for FIDO webauthn signature verification support; ok markus@

OpenBSD-Commit-ID: c9f478fd8e0c1bd17e511ce8694f010d8e32043e

diff --git a/ssh-ecdsa-sk.c b/ssh-ecdsa-sk.c
index 981d60d740feff51887939f1f8adb4af5b92ad6c..dcf605ba1cce68e4933b7737df7215d7586644f4 100644 (file)
--- 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