applypatch: Add backup_source parameter to PatchPartition.

And set it to false when installing recovery image via applypatch. We
only need to back up the source partition when doing in-place update
(e.g. when updating a given partition under recovery). When installing
recovery image via applypatch, we won't touch the source partition (i.e.
/boot).

Removing the backup step also allows dropping the dac_override_allowed
permission. Previously it was needed due to the access to /cache.
Because applypatch runs as root:root, while /cache is owned by
system:cache with 0770.

Bug: 68319577
Test: Invoke the code that installs recovery image; check that recovery
      is installed successfully without denials.
Test: recovery_unit_test passes on taimen.
Change-Id: I549a770b511762189d6672a2835b6e403d695919

applypatch/applypatch.cpp

@@ -47,7 +47,7 @@
 using namespace std::string_literals;
 
 static bool GenerateTarget(const Partition& target, const FileContents& source_file,
-                           const Value& patch, const Value* bonus_data);
+                           const Value& patch, const Value* bonus_data, bool backup_source);
 
 bool LoadFileContents(const std::string& filename, FileContents* file) {
   // No longer allow loading contents from eMMC partitions.
@@ -266,7 +266,7 @@ int ShowLicenses() {
 }
 
 bool PatchPartition(const Partition& target, const Partition& source, const Value& patch,
-                    const Value* bonus) {
+                    const Value* bonus, bool backup_source) {
   LOG(INFO) << "Patching " << target.name;
 
   // We try to load and check against the target hash first.
@@ -280,7 +280,7 @@ bool PatchPartition(const Partition& target, const Partition& source, const Valu
 
   FileContents source_file;
   if (ReadPartitionToBuffer(source, &source_file, true)) {
-    return GenerateTarget(target, source_file, patch, bonus);
+    return GenerateTarget(target, source_file, patch, bonus, backup_source);
   }
 
   LOG(ERROR) << "Failed to find any match";
@@ -326,7 +326,7 @@ bool FlashPartition(const Partition& partition, const std::string& source_filena
 }
 
 static bool GenerateTarget(const Partition& target, const FileContents& source_file,
-                           const Value& patch, const Value* bonus_data) {
+                           const Value& patch, const Value* bonus_data, bool backup_source) {
   uint8_t expected_sha1[SHA_DIGEST_LENGTH];
   if (ParseSha1(target.hash, expected_sha1) != 0) {
     LOG(ERROR) << "Failed to parse target hash \"" << target.hash << "\"";
@@ -351,11 +351,11 @@ static bool GenerateTarget(const Partition& target, const FileContents& source_f
   }
 
   // We write the original source to cache, in case the partition write is interrupted.
-  if (!CheckAndFreeSpaceOnCache(source_file.data.size())) {
+  if (backup_source && !CheckAndFreeSpaceOnCache(source_file.data.size())) {
     LOG(ERROR) << "Not enough free space on /cache";
     return false;
   }
-  if (!SaveFileContents(Paths::Get().cache_temp_source(), &source_file)) {
+  if (backup_source && !SaveFileContents(Paths::Get().cache_temp_source(), &source_file)) {
     LOG(ERROR) << "Failed to back up source file";
     return false;
   }
@@ -415,7 +415,9 @@ static bool GenerateTarget(const Partition& target, const FileContents& source_f
   }
 
   // Delete the backup copy of the source.
-  unlink(Paths::Get().cache_temp_source().c_str());
+  if (backup_source) {
+    unlink(Paths::Get().cache_temp_source().c_str());
+  }
 
   // Success!
   return true;

applypatch/applypatch_modes.cpp

@@ -87,7 +87,7 @@ static int PatchMode(const std::string& target_emmc, const std::string& source_e
     bonus = std::make_unique<Value>(Value::Type::BLOB, std::move(bonus_contents));
   }
 
-  return PatchPartition(target, source, patch, bonus.get()) ? 0 : 1;
+  return PatchPartition(target, source, patch, bonus.get(), false) ? 0 : 1;
 }
 
 static void Usage() {

applypatch/include/applypatch/applypatch.h

@@ -73,10 +73,11 @@ std::ostream& operator<<(std::ostream& os, const Partition& partition);
 // the 'target' Partition. While patching, it will backup the data on the source partition to
 // /cache, so that the patching could be resumed on interruption even if both of the source and
 // target partitions refer to the same device. The function is idempotent if called multiple times.
-// An optional arg 'bonus' can be provided, if the patch was generated with a bonus output.
-// Returns the patching result.
+// 'bonus' can be provided if the patch was generated with a bonus output, or nullptr.
+// 'backup_source' indicates whether the source partition should be backed up prior to the update
+// (e.g. when doing in-place update). Returns the patching result.
 bool PatchPartition(const Partition& target, const Partition& source, const Value& patch,
-                    const Value* bonus);
+                    const Value* bonus, bool backup_source);
 
 // Returns whether the contents of the eMMC target or the cached file match the embedded hash.
 // It will look for the backup on /cache if the given partition doesn't match the checksum.

tests/unit/applypatch_test.cpp

@@ -141,7 +141,7 @@ TEST_F(ApplyPatchTest, PatchPartition) {
   ASSERT_TRUE(LoadFileContents(from_testdata_base("bonus.file"), &bonus_fc));
   Value bonus(Value::Type::BLOB, std::string(bonus_fc.data.cbegin(), bonus_fc.data.cend()));
 
-  ASSERT_TRUE(PatchPartition(target_partition, source_partition, patch, &bonus));
+  ASSERT_TRUE(PatchPartition(target_partition, source_partition, patch, &bonus, false));
 }
 
 // Tests patching an eMMC target without a separate bonus file (i.e. recovery-from-boot patch has
@@ -151,7 +151,7 @@ TEST_F(ApplyPatchTest, PatchPartitionWithoutBonusFile) {
   ASSERT_TRUE(LoadFileContents(from_testdata_base("recovery-from-boot-with-bonus.p"), &patch_fc));
   Value patch(Value::Type::BLOB, std::string(patch_fc.data.cbegin(), patch_fc.data.cend()));
 
-  ASSERT_TRUE(PatchPartition(target_partition, source_partition, patch, nullptr));
+  ASSERT_TRUE(PatchPartition(target_partition, source_partition, patch, nullptr, false));
 }
 
 class FreeCacheTest : public ::testing::Test {

updater/install.cpp

@@ -271,7 +271,7 @@ Value* PatchPartitionFn(const char* name, State* state,
     return StringValue("");
   }
 
-  bool result = PatchPartition(target, source, *values[0], nullptr);
+  bool result = PatchPartition(target, source, *values[0], nullptr, true);
   return StringValue(result ? "t" : "");
 }