Defer CE key fixations to checkpoint commit

On the first boot after an upgrade, ensure that any Keystore key
deletions triggered by fscrypt_set_user_key_protection() are deferred
until the userdata filesystem checkpoint is committed, so that the
system doesn't end up in a bad state if the checkpoint is rolled back.

Test: see I77d30f9be57de7b7c4818680732331549ecb73c8
Bug: 232452368
Ignore-AOSP-First: depends on other changes in internal master
Change-Id: I59b758bc13b7a2ae270f1a6c409affe2eb61119c

Checkpoint.cpp

@@ -16,6 +16,8 @@
 
 #define LOG_TAG "Checkpoint"
 #include "Checkpoint.h"
+#include "FsCrypt.h"
+#include "KeyStorage.h"
 #include "VoldUtil.h"
 #include "VolumeManager.h"
 
@@ -78,6 +80,18 @@ bool setBowState(std::string const& block_device, std::string const& state) {
     return true;
 }
 
+// Do any work that was deferred until the userdata filesystem checkpoint was
+// committed.  This work involves the deletion of resources that aren't covered
+// by the userdata filesystem checkpoint, e.g. Keystore keys.
+void DoCheckpointCommittedWork() {
+    // Take the crypt lock to provide synchronization with the Binder calls that
+    // operate on key directories.
+    std::lock_guard<std::mutex> lock(VolumeManager::Instance()->getCryptLock());
+
+    DeferredCommitKeystoreKeys();
+    fscrypt_deferred_fixate_ce_keys();
+}
+
 }  // namespace
 
 Status cp_supportsCheckpoint(bool& result) {
@@ -205,6 +219,7 @@ Status cp_commitChanges() {
     if (!android::base::RemoveFileIfExists(kMetadataCPFile, &err_str))
         return error(err_str.c_str());
 
+    std::thread(DoCheckpointCommittedWork).detach();
     return Status::ok();
 }
 

FsCrypt.cpp

@@ -16,6 +16,7 @@
 
 #include "FsCrypt.h"
 
+#include "Checkpoint.h"
 #include "KeyStorage.h"
 #include "KeyUtil.h"
 #include "Utils.h"
@@ -112,6 +113,9 @@ EncryptionPolicy s_device_policy;
 std::map<userid_t, EncryptionPolicy> s_de_policies;
 std::map<userid_t, EncryptionPolicy> s_ce_policies;
 
+// CE key fixation operations that have been deferred to checkpoint commit
+std::map<std::string, std::string> s_deferred_fixations;
+
 }  // namespace
 
 // Returns KeyGeneration suitable for key as described in EncryptionOptions
@@ -214,6 +218,7 @@ static bool read_and_fixate_user_ce_key(userid_t user_id,
         LOG(DEBUG) << "Trying user CE key " << ce_key_path;
         if (retrieveKey(ce_key_path, auth, ce_key)) {
             LOG(DEBUG) << "Successfully retrieved key";
+            s_deferred_fixations.erase(directory_path);
             fixate_user_ce_key(directory_path, ce_key_path, paths);
             return true;
         }
@@ -676,6 +681,7 @@ bool fscrypt_destroy_user_key(userid_t user_id) {
                 success &= android::vold::destroyKey(path);
             }
         }
+        s_deferred_fixations.erase(ce_path);
         success &= destroy_dir(ce_path);
 
         auto de_key_path = get_de_key_path(user_id);
@@ -815,13 +821,37 @@ bool fscrypt_set_user_key_protection(userid_t user_id, const std::string& secret
     std::string ce_key_path;
     if (!get_ce_key_new_path(directory_path, paths, &ce_key_path)) return false;
     if (!android::vold::storeKeyAtomically(ce_key_path, user_key_temp, *auth, ce_key)) return false;
-    if (!fixate_user_ce_key(directory_path, ce_key_path, paths)) return false;
+
+    // Fixate the key, i.e. delete all other bindings of it.  (In practice this
+    // just means the kEmptyAuthentication binding, if there is one.)  However,
+    // if a userdata filesystem checkpoint is pending, then we need to delay the
+    // fixation until the checkpoint has been committed, since deleting keys
+    // from Keystore cannot be rolled back.
+    if (android::vold::cp_needsCheckpoint()) {
+        LOG(INFO) << "Deferring fixation of " << directory_path << " until checkpoint is committed";
+        s_deferred_fixations[directory_path] = ce_key_path;
+    } else {
+        s_deferred_fixations.erase(directory_path);
+        if (!fixate_user_ce_key(directory_path, ce_key_path, paths)) return false;
+    }
+
     if (s_new_ce_keys.erase(user_id)) {
         LOG(INFO) << "Stored CE key for new user " << user_id;
     }
     return true;
 }
 
+void fscrypt_deferred_fixate_ce_keys() {
+    for (const auto& it : s_deferred_fixations) {
+        const auto& directory_path = it.first;
+        const auto& to_fix = it.second;
+        LOG(INFO) << "Doing deferred fixation of " << directory_path;
+        fixate_user_ce_key(directory_path, to_fix, get_ce_key_paths(directory_path));
+        // Continue on error.
+    }
+    s_deferred_fixations.clear();
+}
+
 std::vector<int> fscrypt_get_unlocked_users() {
     std::vector<int> user_ids;
     for (const auto& it : s_ce_policies) {

FsCrypt.h

@@ -26,6 +26,7 @@ extern bool fscrypt_init_user0_done;
 bool fscrypt_vold_create_user_key(userid_t user_id, int serial, bool ephemeral);
 bool fscrypt_destroy_user_key(userid_t user_id);
 bool fscrypt_set_user_key_protection(userid_t user_id, const std::string& secret);
+void fscrypt_deferred_fixate_ce_keys();
 
 std::vector<int> fscrypt_get_unlocked_users();
 bool fscrypt_unlock_user_key(userid_t user_id, int serial, const std::string& secret);

KeyStorage.cpp

@@ -23,7 +23,6 @@
 #include <algorithm>
 #include <memory>
 #include <mutex>
-#include <thread>
 #include <vector>
 
 #include <errno.h>
@@ -231,9 +230,8 @@ static bool CommitUpgradedKey(Keystore& keystore, const std::string& dir) {
     return true;
 }
 
-static void DeferredCommitKeys() {
-    android::base::WaitForProperty("vold.checkpoint_committed", "1");
-    LOG(INFO) << "Committing upgraded keys";
+void DeferredCommitKeystoreKeys() {
+    LOG(INFO) << "Committing upgraded Keystore keys";
     Keystore keystore;
     if (!keystore) {
         LOG(ERROR) << "Failed to open Keystore; old keys won't be deleted from Keystore";
@@ -241,10 +239,11 @@ static void DeferredCommitKeys() {
     }
     std::lock_guard<std::mutex> lock(key_upgrade_lock);
     for (auto& dir : key_dirs_to_commit) {
-        LOG(INFO) << "Committing upgraded key " << dir;
+        LOG(INFO) << "Committing upgraded Keystore key for " << dir;
         CommitUpgradedKey(keystore, dir);
     }
     key_dirs_to_commit.clear();
+    LOG(INFO) << "Done committing upgraded Keystore keys";
 }
 
 // Returns true if the Keystore key in |dir| has already been upgraded and is
@@ -260,7 +259,6 @@ static bool IsKeyCommitPending(const std::string& dir) {
 // that key_upgrade_lock is held and that a commit isn't already pending for the
 // directory.
 static void ScheduleKeyCommit(const std::string& dir) {
-    if (key_dirs_to_commit.empty()) std::thread(DeferredCommitKeys).detach();
     key_dirs_to_commit.push_back(dir);
 }
 

KeyStorage.h

@@ -41,6 +41,8 @@ extern const KeyAuthentication kEmptyAuthentication;
 bool createSecdiscardable(const std::string& path, std::string* hash);
 bool readSecdiscardable(const std::string& path, std::string* hash);
 
+void DeferredCommitKeystoreKeys();
+
 // Renames a key directory while also managing deferred commits appropriately.
 // This method should be used whenever a key directory needs to be moved/renamed.
 bool RenameKeyDir(const std::string& old_name, const std::string& new_name);