recovery: allow A/B updater to downgrade

Change-Id: Iaa1fb7838fb958e69fb3104fef7743aafad12b1b

install/include/install/install.h

@@ -64,7 +64,8 @@ bool ReadMetadataFromPackage(ZipArchiveHandle zip, std::map<std::string, std::st
 // Checks if the metadata in the OTA package has expected values. Mandatory checks: ota-type,
 // pre-device and serial number (if presents). A/B OTA specific checks: pre-build version,
 // fingerprint, timestamp.
-bool CheckPackageMetadata(const std::map<std::string, std::string>& metadata, OtaType ota_type);
+bool CheckPackageMetadata(const std::map<std::string, std::string>& metadata, OtaType ota_type,
+                          RecoveryUI* ui);
 
 // Ensures the path to the update package is mounted. Also set the |should_use_fuse| to true if the
 // package stays on a removable media.

install/install.cpp

@@ -63,6 +63,7 @@
 using namespace std::chrono_literals;
 
 bool ask_to_continue_unverified(Device* device);
+bool ask_to_continue_downgrade(Device* device);
 
 static constexpr int kRecoveryApiVersion = 3;
 // We define RECOVERY_API_VERSION in Android.mk, which will be picked up by build system and packed
@@ -150,7 +151,8 @@ static void ReadSourceTargetBuild(const std::map<std::string, std::string>& meta
 // Checks the build version, fingerprint and timestamp in the metadata of the A/B package.
 // Downgrading is not allowed unless explicitly enabled in the package and only for
 // incremental packages.
-static bool CheckAbSpecificMetadata(const std::map<std::string, std::string>& metadata) {
+static bool CheckAbSpecificMetadata(const std::map<std::string, std::string>& metadata,
+                                    RecoveryUI* ui) {
   // Incremental updates should match the current build.
   auto device_pre_build = android::base::GetProperty("ro.build.version.incremental", "");
   auto pkg_pre_build = get_value(metadata, "pre-build-incremental");
@@ -170,6 +172,7 @@ static bool CheckAbSpecificMetadata(const std::map<std::string, std::string>& me
   }
 
   // Check for downgrade version.
+  bool undeclared_downgrade = false;
   int64_t build_timestamp =
       android::base::GetIntProperty("ro.build.date.utc", std::numeric_limits<int64_t>::max());
   int64_t pkg_post_timestamp = 0;
@@ -184,18 +187,23 @@ static bool CheckAbSpecificMetadata(const std::map<std::string, std::string>& me
                     "newer than timestamp "
                  << build_timestamp << " but package has timestamp " << pkg_post_timestamp
                  << " and downgrade not allowed.";
-      return false;
+      undeclared_downgrade = true;
-    }
+    } else if (pkg_pre_build_fingerprint.empty()) {
-    if (pkg_pre_build_fingerprint.empty()) {
       LOG(ERROR) << "Downgrade package must have a pre-build version set, not allowed.";
-      return false;
+      undeclared_downgrade = true;
     }
   }
 
+  if (undeclared_downgrade &&
+      !(ui->IsTextVisible() && ask_to_continue_downgrade(ui->GetDevice()))) {
+    return false;
+  }
+
   return true;
 }
 
-bool CheckPackageMetadata(const std::map<std::string, std::string>& metadata, OtaType ota_type) {
+bool CheckPackageMetadata(const std::map<std::string, std::string>& metadata, OtaType ota_type,
+                          RecoveryUI* ui) {
   auto package_ota_type = get_value(metadata, "ota-type");
   auto expected_ota_type = OtaTypeToString(ota_type);
   if (ota_type != OtaType::AB && ota_type != OtaType::BRICK) {
@@ -252,7 +260,7 @@ bool CheckPackageMetadata(const std::map<std::string, std::string>& metadata, Ot
   }
 
   if (ota_type == OtaType::AB) {
-    return CheckAbSpecificMetadata(metadata);
+    return CheckAbSpecificMetadata(metadata, ui);
   }
 
   return true;
@@ -416,7 +424,7 @@ static InstallResult TryUpdateBinary(Package* package, bool* wipe_cache,
   // Package does not declare itself as an A/B package, but device only supports A/B;
   //   still calls CheckPackageMetadata to get a meaningful error message.
   if (package_is_ab || device_only_supports_ab) {
-    if (!CheckPackageMetadata(metadata, OtaType::AB)) {
+    if (!CheckPackageMetadata(metadata, OtaType::AB, ui)) {
       log_buffer->push_back(android::base::StringPrintf("error: %d", kUpdateBinaryCommandFailure));
       return INSTALL_ERROR;
     }

install/wipe_device.cpp

@@ -169,7 +169,7 @@ static bool CheckWipePackage(Package* wipe_package, RecoveryUI* ui) {
     return false;
   }
 
-  return CheckPackageMetadata(metadata, OtaType::BRICK);
+  return CheckPackageMetadata(metadata, OtaType::BRICK, ui);
 }
 
 bool WipeAbDevice(Device* device, size_t wipe_package_size) {

recovery.cpp

@@ -178,6 +178,15 @@ bool ask_to_continue_unverified(Device* device) {
   }
 }
 
+bool ask_to_continue_downgrade(Device* device) {
+  if (get_build_type() == "user") {
+    return false;
+  } else {
+    device->GetUI()->SetProgressType(RecoveryUI::EMPTY);
+    return yes_no(device, "This package will downgrade your system", "Install anyway?");
+  }
+}
+
 static bool ask_to_wipe_data(Device* device) {
   std::vector<std::string> headers{ "Format user data?", "This includes internal storage.", "THIS CANNOT BE UNDONE!" };
   std::vector<std::string> items{ " Cancel", " Format data" };