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

1 files changed, 9 insertions, 7 deletions

diff --git a/applypatch/applypatch.cpp b/applypatch/applypatch.cpp
index 90d8e860..336860cb 100644
--- a/applypatch/applypatch.cpp
+++ b/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;