Clean package manager caches on boot

Some devices seem to have an issue where (presumably) resources from an
old version are being used with new code. This causes BCR to crash with
an error about the app theme not being derived from Theme.AppCompat.
This commit works around the issue in a brute force way by deleting
BCR's package manager cache entry on every boot.

Fixes: #275, #303, #307

Signed-off-by: Andrew Gunnerson <[email protected]>

app/build.gradle.kts

@@ -350,6 +350,8 @@ android.applicationVariants.all {
             }
         }
 
+        from(File(magiskDir, "boot_common.sh"))
+        from(File(magiskDir, "post-fs-data.sh"))
         from(File(magiskDir, "service.sh"))
 
         from(File(rootDir, "LICENSE"))

app/magisk/boot_common.sh

@@ -0,0 +1,34 @@
+# source "${0%/*}/boot_common.sh" <log file>
+
+exec >"${1}" 2>&1
+
+mod_dir=${0%/*}
+
+header() {
+    echo "----- ${*} -----"
+}
+
+module_prop() {
+    grep "^${1}=" "${mod_dir}/module.prop" | cut -d= -f2
+}
+
+run_cli_apk() {
+    CLASSPATH="${cli_apk}" app_process / "${@}" &
+    pid=${!}
+    wait "${pid}"
+    echo "Exit status: ${?}"
+    echo "Logcat:"
+    logcat -d --pid "${pid}"
+}
+
+app_id=$(module_prop id)
+app_version=$(module_prop version)
+cli_apk=$(echo "${mod_dir}"/system/priv-app/"${app_id}"/app-*.apk)
+
+header Environment
+echo "Timestamp: $(date)"
+echo "Script: ${0}"
+echo "App ID: ${app_id}"
+echo "App version: ${app_version}"
+echo "CLI APK: ${cli_apk}"
+echo "UID/GID/Context: $(id)"

app/magisk/post-fs-data.sh

@@ -0,0 +1,13 @@
+# On some devices, upgrading BCR seems to cause some old state to unexpectedly
+# linger around, causing BCR to crash with an obscure error about the theme not
+# being derived from Theme.AppCompat.
+
+source "${0%/*}/boot_common.sh" /data/local/tmp/bcr_clear_package_manager_caches.log
+
+header Timestamps
+ls -lZ "${cli_apk}"
+ls -lZ "${cli_apk#"${mod_dir}"}"
+find /data/system/package_cache -name "${app_id}-*" -exec ls -lZ {} \+
+
+header Clear package manager caches
+run_cli_apk com.chiller3.bcr.standalone.ClearPackageManagerCachesKt

app/magisk/service.sh

@@ -5,38 +5,10 @@
 # to alter the flags. This command blocks for an arbitrary amount of time
 # because it needs to wait until the primary user unlocks the device.
 
-exec >/data/local/tmp/bcr_remove_hard_restrictions.log 2>&1
-
-mod_dir=${0%/*}
-
-header() {
-    echo "----- ${*} -----"
-}
-
-module_prop() {
-    grep "^${1}=" "${mod_dir}/module.prop" | cut -d= -f2
-}
-
-app_id=$(module_prop id)
-app_version=$(module_prop version)
-
-header Environment
-echo "Timestamp: $(date)"
-echo "Args: ${0} ${*}"
-echo "Version: ${app_version}"
-echo "UID/GID/Context: $(id)"
+source "${0%/*}/boot_common.sh" /data/local/tmp/bcr_remove_hard_restrictions.log
 
 header Remove hard restrictions
-CLASSPATH=$(find "${mod_dir}"/system/priv-app/"${app_id}" -name '*.apk') \
-    app_process \
-    / \
-    com.chiller3.bcr.standalone.RemoveHardRestrictionsKt &
-pid=${!}
-wait "${pid}"
-echo "Exit status: ${?}"
-
-header Logcat
-logcat -d --pid "${pid}"
+run_cli_apk com.chiller3.bcr.standalone.RemoveHardRestrictionsKt
 
 header Package state
 dumpsys package "${app_id}"

app/src/main/java/com/chiller3/bcr/standalone/ClearPackageManagerCaches.kt

@@ -0,0 +1,95 @@
+@file:Suppress("SameParameterValue")
+
+package com.chiller3.bcr.standalone
+
+import com.chiller3.bcr.BuildConfig
+import java.nio.file.Path
+import java.nio.file.Paths
+import kotlin.io.path.ExperimentalPathApi
+import kotlin.io.path.deleteIfExists
+import kotlin.io.path.isRegularFile
+import kotlin.io.path.readBytes
+import kotlin.io.path.walk
+import kotlin.system.exitProcess
+
+private val PACKAGE_CACHE_DIR = Paths.get("/data/system/package_cache")
+
+private var dryRun = false
+
+private fun delete(path: Path) {
+    if (dryRun) {
+        println("Would have deleted: $path")
+    } else {
+        println("Deleting: $path")
+        path.deleteIfExists()
+    }
+}
+
+private fun ByteArray.indexOfSubarray(needle: ByteArray, start: Int = 0): Int {
+    require(start >= 0) { "start must be non-negative" }
+
+    if (needle.isEmpty()) {
+        return 0
+    }
+
+    outer@ for (i in 0 until size - needle.size + 1) {
+        for (j in needle.indices) {
+            if (this[i + j] != needle[j]) {
+                continue@outer
+            }
+        }
+        return i
+    }
+
+    return -1
+}
+
+@OptIn(ExperimentalPathApi::class)
+private fun clearPackageManagerCache(appId: String): Boolean {
+    // The current implementation of the package cache uses PackageImpl.writeToParcel(), which
+    // serializes the cache entry to the file as a Parcel. The current Parcel implementation stores
+    // string values as null-terminated little-endian UTF-16. One of the string values stored is
+    // manifestPackageName, which we can match on.
+    //
+    // This is a unique enough search that there should never be a false positive, but even if there
+    // is, the package manager will just repopulate the cache.
+    val needle = "\u0000$appId\u0000".toByteArray(Charsets.UTF_16LE)
+    var ret = true
+
+    for (path in PACKAGE_CACHE_DIR.walk()) {
+        if (!path.isRegularFile()) {
+            continue
+        }
+
+        try {
+            // Not the most efficient, but these are tiny files that Android is later going to read
+            // entirely into memory anyway
+            if (path.readBytes().indexOfSubarray(needle) >= 0) {
+                delete(path)
+            }
+        } catch (e: Exception) {
+            e.printStackTrace()
+            ret = false
+        }
+    }
+
+    return ret
+}
+
+private fun mainInternal() {
+    clearPackageManagerCache(BuildConfig.APPLICATION_ID)
+}
+
+fun main(args: Array<String>) {
+    if ("--dry-run" in args) {
+        dryRun = true
+    }
+
+    try {
+        mainInternal()
+    } catch (e: Exception) {
+        System.err.println("Failed to clear caches")
+        e.printStackTrace()
+        exitProcess(1)
+    }
+}

app/src/main/java/com/chiller3/bcr/standalone/RemoveHardRestrictions.kt

@@ -272,7 +272,7 @@ private fun waitForLogin(userId: Int) {
         "User $userId did not unlock the device after $IS_USER_UNLOCKED_ATTEMPTS attempts")
 }
 
-fun mainInternal() {
+private fun mainInternal() {
     if (Build.VERSION.SDK_INT == Build.VERSION_CODES.P) {
         println("Android 9 does not have hard-restricted permissions")
         return