From ea2b3d3178afc466c5ee5db3b3f76f012e622a20 Mon Sep 17 00:00:00 2001
From: Rahul Frias <rfrias@google.com>
Date: Mon, 2 Nov 2020 01:39:13 -0800
Subject: [PATCH] Sign fake license request if usage tables are not supported

Merge of http://go/wvgerrit/106823

Previously, we worked around a problem by signing a fake license
request when a license did not have a usage entry. However, this was
inside a conditional that the device did support usage tables. This CL
moves that code outside the conditional so that a fake license is
signed whenever the license does not have an entry.

Bug: 169591716
Test: unit and integration tests
Change-Id: Ic4d1a91af63503722b088a136c0a8dca9746a962
---
 libwvdrmengine/cdm/core/src/cdm_session.cpp | 29 ++++++++++++++-------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/libwvdrmengine/cdm/core/src/cdm_session.cpp b/libwvdrmengine/cdm/core/src/cdm_session.cpp
index 7bf0647a..4edc8e73 100644
--- a/libwvdrmengine/cdm/core/src/cdm_session.cpp
+++ b/libwvdrmengine/cdm/core/src/cdm_session.cpp
@@ -336,20 +336,13 @@ CdmResponseType CdmSession::RestoreOfflineSession(const CdmKeySetId& key_set_id,
   }
 
   std::string provider_session_token;
+  bool sign_fake_request = false;  // TODO(b/169483174): remove this variable.
   if (usage_support_type_ == kUsageEntrySupport) {
     if (!license_parser_->ExtractProviderSessionToken(
             key_response_, &provider_session_token) ||
         usage_table_header_ == nullptr) {
       provider_session_token.clear();
-      // TODO(b/161023174): remove this code in v17.
-      std::string fake_message("empty message");
-      std::string core_message;
-      std::string license_request_signature;
-      // Sign a fake message so that OEMCrypto will start the rental clock. The
-      // signature and generated core message are ignored.
-      CdmResponseType status = crypto_session_->PrepareAndSignLicenseRequest(
-          fake_message, &core_message, &license_request_signature);
-      if (status != NO_ERROR) return status;
+      sign_fake_request = true;  // TODO(b/169483174): remove this line.
     } else if (!VerifyOfflineUsageEntry()) {
       LOGE("License usage entry is invalid, cannot restore");
       return LICENSE_USAGE_ENTRY_MISSING;
@@ -362,6 +355,24 @@ CdmResponseType CdmSession::RestoreOfflineSession(const CdmKeySetId& key_set_id,
         return sts;
       }
     }
+  } else {
+    sign_fake_request = true;  // TODO(b/169483174): remove this block.
+  }
+  // TODO(b/169483174): remove this code in v17. For OEMCrypto v16, an offline
+  // license would not work because the rental clock in OEMCrypto is only
+  // started when the license request is signed. We will sign a fake license
+  // request if the device does not support usage tables, or if the license does
+  // not have a usage entry.
+  if (sign_fake_request) {
+    std::string fake_message("empty message");
+    std::string core_message;
+    std::string license_request_signature;
+    // Sign a fake message so that OEMCrypto will start the rental clock. The
+    // signature and generated core message are ignored.
+    const CdmResponseType status =
+        crypto_session_->PrepareAndSignLicenseRequest(
+            fake_message, &core_message, &license_request_signature);
+    if (status != NO_ERROR) return status;
   }
 
   CdmResponseType result;