Restrict the verification in block-based incremental OTAs

BlockImageDiff has three versions. Only the incremental OTAs generated
with the latest version (3) can be re-applied to the system that's
already on the target build. Otherwise, operations like move will make
unconditional changes and damage the system. During the verification
phase, abort the OTA update if BlockImageDiff is less than 3 and it
doesn't match the checksum of the source build.

Change-Id: Ic630346eab2a993a84d0aeaacd7167ef62cc24f6
(cherry picked from commit daebaa6ed3)

tools/releasetools/common.py

@@ -1024,17 +1024,19 @@ def ComputeDifferences(diffs):
 
 
 class BlockDifference:
-  def __init__(self, partition, tgt, src=None, check_first_block=False):
+  def __init__(self, partition, tgt, src=None, check_first_block=False, version=None):
     self.tgt = tgt
     self.src = src
     self.partition = partition
     self.check_first_block = check_first_block
 
-    self.version = 1
+    if version is None:
+      version = 1
       if OPTIONS.info_dict:
-      self.version = max(
+        version = max(
             int(i) for i in
             OPTIONS.info_dict.get("blockimgdiff_versions", "1").split(","))
+    self.version = version
 
     b = blockimgdiff.BlockImageDiff(tgt, src, threads=OPTIONS.worker_threads,
                                     version=self.version)
@@ -1069,17 +1071,25 @@ class BlockDifference:
         script.AppendExtra('if range_sha1("%s", "%s") == "%s" then' %
                             (self.device, self.src.care_map.to_string_raw(),
                             self.src.TotalSha1()))
-      script.Print("Verified %s image..." % (partition,))
+      script.Print('Verified %s image...' % (partition,))
       script.AppendExtra('else');
 
+      # When generating incrementals for the system and vendor partitions,
+      # explicitly check the first block (which contains the superblock) of
+      # the partition to see if it's what we expect. If this check fails,
+      # give an explicit log message about the partition having been
+      # remounted R/W (the most likely explanation) and the need to flash to
+      # get OTAs working again.
       if self.check_first_block:
         self._CheckFirstBlock(script)
 
-      script.AppendExtra(('(range_sha1("%s", "%s") == "%s") ||\n'
+      # Abort the OTA update. Note that the incremental OTA cannot be applied
-                          '  abort("%s partition has unexpected contents");\n'
+      # even if it may match the checksum of the target partition.
-                          'endif;') %
+      # a) If version < 3, operations like move and erase will make changes
-                         (self.device, self.tgt.care_map.to_string_raw(),
+      #    unconditionally and damage the partition.
-                          self.tgt.TotalSha1(), self.partition))
+      # b) If version >= 3, it won't even reach here.
+      script.AppendExtra(('abort("%s partition has unexpected contents");\n'
+                          'endif;') % (partition,))
 
   def _WriteUpdate(self, script, output_zip):
     partition = self.partition
@@ -1109,14 +1119,11 @@ class BlockDifference:
   def _CheckFirstBlock(self, script):
     r = RangeSet((0, 1))
     srchash = self._HashBlocks(self.src, r);
-    tgthash = self._HashBlocks(self.tgt, r);
 
     script.AppendExtra(('(range_sha1("%s", "%s") == "%s") || '
-                        '(range_sha1("%s", "%s") == "%s") || '
                         'abort("%s has been remounted R/W; '
                         'reflash device to reenable OTA updates");')
                        % (self.device, r.to_string_raw(), srchash,
-                          self.device, r.to_string_raw(), tgthash,
                           self.device))
 
 DataImage = blockimgdiff.DataImage

tools/releasetools/ota_from_target_files

@@ -740,8 +740,16 @@ def WriteBlockIncrementalOTAPackage(target_zip, source_zip, output_zip):
 
   system_src = GetImage("system", OPTIONS.source_tmp, OPTIONS.source_info_dict)
   system_tgt = GetImage("system", OPTIONS.target_tmp, OPTIONS.target_info_dict)
+
+  blockimgdiff_version = 1
+  if OPTIONS.info_dict:
+    blockimgdiff_version = max(
+        int(i) for i in
+        OPTIONS.info_dict.get("blockimgdiff_versions", "1").split(","))
+
   system_diff = common.BlockDifference("system", system_tgt, system_src,
-                                       check_first_block=True)
+                                       check_first_block=True,
+                                       version=blockimgdiff_version)
 
   if HasVendorPartition(target_zip):
     if not HasVendorPartition(source_zip):
@@ -749,7 +757,8 @@ def WriteBlockIncrementalOTAPackage(target_zip, source_zip, output_zip):
     vendor_src = GetImage("vendor", OPTIONS.source_tmp, OPTIONS.source_info_dict)
     vendor_tgt = GetImage("vendor", OPTIONS.target_tmp, OPTIONS.target_info_dict)
     vendor_diff = common.BlockDifference("vendor", vendor_tgt, vendor_src,
-                                         check_first_block=True)
+                                         check_first_block=True,
+                                         version=blockimgdiff_version)
   else:
     vendor_diff = None
 
@@ -810,7 +819,18 @@ else if get_stage("%(bcb_dev)s") != "3/3" then
   device_specific.IncrementalOTA_VerifyBegin()
 
   if oem_props is None:
+    # When blockimgdiff version is less than 3 (non-resumable block-based OTA),
+    # patching on a device that's already on the target build will damage the
+    # system. Because operations like move don't check the block state, they
+    # always apply the changes unconditionally.
+    if blockimgdiff_version <= 2:
+      script.AssertSomeFingerprint(source_fp)
+    else:
       script.AssertSomeFingerprint(source_fp, target_fp)
+  else:
+    if blockimgdiff_version <= 2:
+      script.AssertSomeThumbprint(
+          GetBuildProp("ro.build.thumbprint", OPTIONS.source_info_dict))
     else:
       script.AssertSomeThumbprint(
           GetBuildProp("ro.build.thumbprint", OPTIONS.target_info_dict),