Check trailing data when parsing ASN.1.

content/child/webcrypto/nss/rsa_key_nss.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/child/webcrypto/nss/rsa_key_nss.h"
 
+#include <secasn1.h>
+
 #include "base/logging.h"
 #include "content/child/webcrypto/crypto_data.h"
 #include "content/child/webcrypto/generate_key_result.h"
 #include "content/child/webcrypto/jwk.h"
 #include "content/child/webcrypto/nss/key_nss.h"
 #include "content/child/webcrypto/nss/util_nss.h"
 #include "content/child/webcrypto/status.h"
 #include "content/child/webcrypto/webcrypto_util.h"
 #include "crypto/scoped_nss_types.h"
 #include "third_party/WebKit/public/platform/WebCryptoAlgorithmParams.h"
@@ skipping 616 matching lines @@
     bool extractable,
     blink::WebCryptoKeyUsageMask usages,
     blink::WebCryptoKey* key) const {
   Status status = NssSupportsRsaPrivateKeyImport();
   if (status.IsError())
     return status;
 
   if (!key_data.byte_length())
     return Status::ErrorImportEmptyKeyData();
 
+  crypto::ScopedPLArenaPool arena(PORT_NewArena(DER_DEFAULT_CHUNKSIZE));
+  if (!arena.get())
+    return Status::OperationError();
+
   // The binary blob 'key_data' is expected to be a DER-encoded ASN.1 PKCS#8
-  // private key info object.
-  SECItem pki_der = MakeSECItemForBuffer(key_data);
+  // private key info object. Excess data is illegal, but NSS silently accepts
+  // it, so first ensure that 'key_data' consists of a single ASN.1 element.
+  SECItem key_item = MakeSECItemForBuffer(key_data);
+  SECItem pki_der;
+  if (SEC_QuickDERDecodeItem(arena.get(),
+                             &pki_der,
+                             SEC_ASN1_GET(SEC_AnyTemplate),

[davidben, 2014/11/07 23:37:45]

This seems silly, but I'm not familiar enough with NSS to know if there's a
better way to peel off an element.

+                             &key_item) != SECSuccess) {
+    return Status::DataError();
+  }
 
   SECKEYPrivateKey* seckey_private_key = NULL;
   crypto::ScopedPK11Slot slot(PK11_GetInternalSlot());
   if (PK11_ImportDERPrivateKeyInfoAndReturnKey(slot.get(),
                                                &pki_der,
                                                NULL,    // nickname
                                                NULL,    // publicValue
                                                false,   // isPerm
                                                false,   // isPrivate
                                                KU_ALL,  // usage
@@ skipping 187 matching lines @@
       return Status::Success();
     }
     default:
       return Status::ErrorUnexpected();
   }
 }
 
 }  // namespace webcrypto
 
 }  // namespace content