schannel: verify hostname independent of verify cert

Prior to this change when CURLOPT_SSL_VERIFYPEER (verifypeer) was off
and CURLOPT_SSL_VERIFYHOST (verifyhost) was on we did not verify the
hostname in schannel code.

This fixes KNOWN_BUG 2.8 "Schannel disable CURLOPT_SSL_VERIFYPEER and
verify hostname". We discussed a fix several years ago in #3285 but it
went stale.

Assisted-by: Daniel Stenberg

Bug: https://curl.haxx.se/mail/lib-2018-10/0113.html
Reported-by: Martin Galvan

Ref: https://github.com/curl/curl/pull/3285

Fixes https://github.com/curl/curl/issues/3284
Closes https://github.com/curl/curl/pull/10056

docs/KNOWN_BUGS

@@ -21,7 +21,6 @@ problems may have been fixed or changed somewhat since this was written.
  2.4 Secure Transport will not import PKCS#12 client certificates without a password
  2.5 Client cert handling with Issuer DN differs between backends
  2.7 Client cert (MTLS) issues with Schannel
- 2.8 Schannel disable CURLOPT_SSL_VERIFYPEER and verify hostname
  2.11 Schannel TLS 1.2 handshake bug in old Windows versions
  2.12 FTPS with Schannel times out file list operation
  2.13 CURLOPT_CERTINFO results in CURLE_OUT_OF_MEMORY with Schannel
@@ -163,12 +162,6 @@ problems may have been fixed or changed somewhat since this was written.
 
  See https://github.com/curl/curl/issues/3145
 
-2.8 Schannel disable CURLOPT_SSL_VERIFYPEER and verify hostname
-
- This seems to be a limitation in the underlying Schannel API.
-
- https://github.com/curl/curl/issues/3284
-
 2.11 Schannel TLS 1.2 handshake bug in old Windows versions
 
  In old versions of Windows such as 7 and 8.1 the Schannel TLS 1.2 handshake

lib/vtls/schannel.c

@@ -810,9 +810,9 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
 
     SCH_CREDENTIALS credentials = { 0 };
     TLS_PARAMETERS tls_parameters = { 0 };
-    CRYPTO_SETTINGS crypto_settings[4] = { 0 };
+    CRYPTO_SETTINGS crypto_settings[4] = { { 0 } };
-    UNICODE_STRING blocked_ccm_modes[1] = { 0 };
+    UNICODE_STRING blocked_ccm_modes[1] = { { 0 } };
-    UNICODE_STRING blocked_gcm_modes[1] = { 0 };
+    UNICODE_STRING blocked_gcm_modes[1] = { { 0 } };
 
     int crypto_settings_idx = 0;
 
@@ -1634,10 +1634,16 @@ schannel_connect_step2(struct Curl_cfilter *cf, struct Curl_easy *data)
 
 #ifdef HAS_MANUAL_VERIFY_API
   if(conn_config->verifypeer && backend->use_manual_cred_validation) {
+    /* Certificate verification also verifies the hostname if verifyhost */
     return Curl_verify_certificate(cf, data);
   }
 #endif
 
+  /* Verify the hostname manually when certificate verification is disabled,
+     because in that case Schannel won't verify it. */
+  if(!conn_config->verifypeer && conn_config->verifyhost)
+    return Curl_verify_host(cf, data);
+
   return CURLE_OK;
 }
 

lib/vtls/schannel.h

@@ -76,6 +76,9 @@
 
 extern const struct Curl_ssl Curl_ssl_schannel;
 
+CURLcode Curl_verify_host(struct Curl_cfilter *cf,
+                          struct Curl_easy *data);
+
 CURLcode Curl_verify_certificate(struct Curl_cfilter *cf,
                                  struct Curl_easy *data);
 

lib/vtls/schannel_int.h

@@ -43,6 +43,58 @@
 #define HAS_CLIENT_CERT_PATH
 #endif
 
+#ifndef CRYPT_DECODE_NOCOPY_FLAG
+#define CRYPT_DECODE_NOCOPY_FLAG 0x1
+#endif
+
+#ifndef CRYPT_DECODE_ALLOC_FLAG
+#define CRYPT_DECODE_ALLOC_FLAG 0x8000
+#endif
+
+#ifndef CERT_ALT_NAME_DNS_NAME
+#define CERT_ALT_NAME_DNS_NAME 3
+#endif
+
+#ifndef CERT_ALT_NAME_IP_ADDRESS
+#define CERT_ALT_NAME_IP_ADDRESS 8
+#endif
+
+
+#if defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR)
+/* Original mingw is missing CERT structs or they're disabled.
+   Refer to w32api-5.0.2-mingw32-dev\include\wincrypt.h. */
+
+/* !checksrc! disable TYPEDEFSTRUCT 4 */
+typedef struct _CERT_OTHER_NAME {
+  LPSTR pszObjId;
+  CRYPT_OBJID_BLOB Value;
+} CERT_OTHER_NAME, *PCERT_OTHER_NAME;
+
+typedef struct _CERT_ALT_NAME_ENTRY {
+  DWORD dwAltNameChoice;
+  union {
+    PCERT_OTHER_NAME pOtherName;
+    LPWSTR pwszRfc822Name;
+    LPWSTR pwszDNSName;
+    CERT_NAME_BLOB DirectoryName;
+    LPWSTR pwszURL;
+    CRYPT_DATA_BLOB IPAddress;
+    LPSTR pszRegisteredID;
+  };
+} CERT_ALT_NAME_ENTRY, *PCERT_ALT_NAME_ENTRY;
+
+typedef struct _CERT_ALT_NAME_INFO {
+  DWORD cAltEntry;
+  PCERT_ALT_NAME_ENTRY rgAltEntry;
+} CERT_ALT_NAME_INFO, *PCERT_ALT_NAME_INFO;
+
+typedef struct _CRYPT_DECODE_PARA {
+  DWORD cbSize;
+  PFN_CRYPT_ALLOC pfnAlloc;
+  PFN_CRYPT_FREE pfnFree;
+} CRYPT_DECODE_PARA, *PCRYPT_DECODE_PARA;
+#endif
+
 #ifndef SCH_CREDENTIALS_VERSION
 
 #define SCH_CREDENTIALS_VERSION  0x00000005

lib/vtls/schannel_verify.c

@@ -39,8 +39,6 @@
 #include "schannel.h"
 #include "schannel_int.h"
 
-#ifdef HAS_MANUAL_VERIFY_API
-
 #include "vtls.h"
 #include "vtls_int.h"
 #include "sendf.h"
@@ -56,6 +54,9 @@
 
 #define BACKEND ((struct schannel_ssl_backend_data *)connssl->backend)
 
+
+#ifdef HAS_MANUAL_VERIFY_API
+
 #define MAX_CAFILE_SIZE 1048576 /* 1 MiB */
 #define BEGIN_CERT "-----BEGIN CERTIFICATE-----"
 #define END_CERT "\n-----END CERTIFICATE-----"
@@ -330,6 +331,8 @@ cleanup:
   return result;
 }
 
+#endif /* HAS_MANUAL_VERIFY_API */
+
 /*
  * Returns the number of characters necessary to populate all the host_names.
  * If host_names is not NULL, populate it with all the host names. Each string
@@ -353,10 +356,10 @@ static DWORD cert_get_name_string(struct Curl_easy *data,
   LPTSTR current_pos = NULL;
   DWORD i;
 
+#ifdef CERT_NAME_SEARCH_ALL_NAMES_FLAG
   /* CERT_NAME_SEARCH_ALL_NAMES_FLAG is available from Windows 8 onwards. */
   if(curlx_verify_windows_version(6, 2, 0, PLATFORM_WINNT,
                                   VERSION_GREATER_THAN_EQUAL)) {
-#ifdef CERT_NAME_SEARCH_ALL_NAMES_FLAG
     /* CertGetNameString will provide the 8-bit character string without
      * any decoding */
     DWORD name_flags =
@@ -368,8 +371,8 @@ static DWORD cert_get_name_string(struct Curl_easy *data,
                                       host_names,
                                       length);
     return actual_length;
-#endif
   }
+#endif
 
   compute_content = host_names != NULL && length != 0;
 
@@ -457,17 +460,34 @@ static DWORD cert_get_name_string(struct Curl_easy *data,
   return actual_length;
 }
 
-static CURLcode verify_host(struct Curl_easy *data,
+/* Verify the server's hostname */
-                            CERT_CONTEXT *pCertContextServer,
+CURLcode Curl_verify_host(struct Curl_cfilter *cf,
-                            const char *conn_hostname)
+                          struct Curl_easy *data)
 {
+  struct ssl_connect_data *connssl = cf->ctx;
+  SECURITY_STATUS sspi_status;
   CURLcode result = CURLE_PEER_FAILED_VERIFICATION;
+  CERT_CONTEXT *pCertContextServer = NULL;
   TCHAR *cert_hostname_buff = NULL;
   size_t cert_hostname_buff_index = 0;
+  const char *conn_hostname = connssl->hostname;
   size_t hostlen = strlen(conn_hostname);
   DWORD len = 0;
   DWORD actual_len = 0;
 
+  sspi_status =
+    s_pSecFn->QueryContextAttributes(&BACKEND->ctxt->ctxt_handle,
+                                     SECPKG_ATTR_REMOTE_CERT_CONTEXT,
+                                     &pCertContextServer);
+
+  if((sspi_status != SEC_E_OK) || !pCertContextServer) {
+    char buffer[STRERROR_LEN];
+    failf(data, "schannel: Failed to read remote certificate context: %s",
+          Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
+    result = CURLE_PEER_FAILED_VERIFICATION;
+    goto cleanup;
+  }
+
   /* Determine the size of the string needed for the cert hostname */
   len = cert_get_name_string(data, pCertContextServer, NULL, 0);
   if(len == 0) {
@@ -498,10 +518,9 @@ static CURLcode verify_host(struct Curl_easy *data,
     goto cleanup;
   }
 
-  /* If HAVE_CERT_NAME_SEARCH_ALL_NAMES is available, the output
+  /* cert_hostname_buff contains all DNS names, where each name is
-   * will contain all DNS names, where each name is null-terminated
+   * null-terminated and the last DNS name is double null-terminated. Due to
-   * and the last DNS name is double null-terminated. Due to this
+   * this encoding, use the length of the buffer to iterate over all names.
-   * encoding, use the length of the buffer to iterate over all names.
    */
   result = CURLE_PEER_FAILED_VERIFICATION;
   while(cert_hostname_buff_index < len &&
@@ -560,9 +579,15 @@ static CURLcode verify_host(struct Curl_easy *data,
 cleanup:
   Curl_safefree(cert_hostname_buff);
 
+  if(pCertContextServer)
+    CertFreeCertificateContext(pCertContextServer);
+
   return result;
 }
 
+
+#ifdef HAS_MANUAL_VERIFY_API
+/* Verify the server's certificate and hostname */
 CURLcode Curl_verify_certificate(struct Curl_cfilter *cf,
                                  struct Curl_easy *data)
 {
@@ -721,7 +746,7 @@ CURLcode Curl_verify_certificate(struct Curl_cfilter *cf,
 
   if(result == CURLE_OK) {
     if(conn_config->verifyhost) {
-      result = verify_host(data, pCertContextServer, connssl->hostname);
+      result = Curl_verify_host(cf, data);
     }
   }