Patch AndroidManifest.xml properly

Parse and rebuild the string pool of the AXML format for patching
string in AndroidManifest.xml

app/src/main/java/com/topjohnwu/magisk/core/download/ManagerHandler.kt

@@ -10,7 +10,7 @@ import com.topjohnwu.magisk.core.Info
 import com.topjohnwu.magisk.core.download.Action.APK.Restore
 import com.topjohnwu.magisk.core.download.Action.APK.Upgrade
 import com.topjohnwu.magisk.core.isRunningAsStub
-import com.topjohnwu.magisk.core.utils.PatchAPK
+import com.topjohnwu.magisk.core.tasks.PatchAPK
 import com.topjohnwu.magisk.ktx.relaunchApp
 import com.topjohnwu.magisk.ktx.writeTo
 import com.topjohnwu.superuser.Shell
@@ -18,7 +18,7 @@ import java.io.File
 
 private fun Context.patch(apk: File) {
     val patched = File(apk.parent, "patched.apk")
-    PatchAPK.patch(apk.path, patched.path, packageName, applicationInfo.nonLocalizedLabel)
+    PatchAPK.patch(this, apk.path, patched.path, packageName, applicationInfo.nonLocalizedLabel)
     apk.delete()
     patched.renameTo(apk)
 }

app/src/main/java/com/topjohnwu/magisk/core/tasks/PatchAPK.kt

@@ -1,4 +1,4 @@
-package com.topjohnwu.magisk.core.utils
+package com.topjohnwu.magisk.core.tasks
 
 import android.content.Context
 import android.os.Build.VERSION.SDK_INT
@@ -8,6 +8,8 @@ import com.topjohnwu.magisk.core.Config
 import com.topjohnwu.magisk.core.Const
 import com.topjohnwu.magisk.core.Info
 import com.topjohnwu.magisk.core.isRunningAsStub
+import com.topjohnwu.magisk.core.utils.AXML
+import com.topjohnwu.magisk.core.utils.Keygen
 import com.topjohnwu.magisk.data.network.GithubRawServices
 import com.topjohnwu.magisk.ktx.get
 import com.topjohnwu.magisk.ktx.writeTo
@@ -24,8 +26,6 @@ import timber.log.Timber
 import java.io.File
 import java.io.FileOutputStream
 import java.io.IOException
-import java.nio.ByteBuffer
-import java.nio.ByteOrder
 import java.security.SecureRandom
 
 object PatchAPK {
@@ -36,13 +36,15 @@ object PatchAPK {
     private const val APP_ID = "com.topjohnwu.magisk"
     private const val APP_NAME = "Magisk Manager"
 
-    private fun genPackageName(prefix: String, length: Int): CharSequence {
-        val builder = StringBuilder(length)
-        builder.append(prefix)
-        val len = length - prefix.length
+    // Some arbitrary limit
+    const val MAX_LABEL_LENGTH = 32
+
+    private fun genPackageName(): CharSequence {
         val random = SecureRandom()
+        val len = 5 + random.nextInt(15)
+        val builder = StringBuilder(len)
         var next: Char
-        var prev = prefix[prefix.length - 1]
+        var prev = 0.toChar()
         for (i in 0 until len) {
             next = if (prev == '.' || i == len - 1) {
                 ALPHA[random.nextInt(ALPHA.length)]
@@ -52,49 +54,30 @@ object PatchAPK {
             builder.append(next)
             prev = next
         }
+        if (!builder.contains('.')) {
+            // Pick a random index and set it as dot
+            val idx = random.nextInt(len - 1)
+            builder[idx] = '.'
+        }
         return builder
     }
 
-    private fun findAndPatch(xml: ByteArray, from: CharSequence, to: CharSequence): Boolean {
-        if (to.length > from.length)
-            return false
-        val buf = ByteBuffer.wrap(xml).order(ByteOrder.LITTLE_ENDIAN).asCharBuffer()
-        val offList = mutableListOf<Int>()
-        var i = 0
-        loop@ while (i < buf.length - from.length) {
-            for (j in from.indices) {
-                if (buf.get(i + j) != from[j]) {
-                    ++i
-                    continue@loop
-                }
-            }
-            offList.add(i)
-            i += from.length
-        }
-        if (offList.isEmpty())
-            return false
-
-        val toBuf = to.toString().toCharArray().copyOf(from.length)
-        for (off in offList) {
-            buf.position(off)
-            buf.put(toBuf)
-        }
-        return true
-    }
-
-    fun patch(apk: String, out: String, pkg: CharSequence, label: CharSequence): Boolean {
+    fun patch(
+        context: Context,
+        apk: String, out: String,
+        pkg: CharSequence, label: CharSequence
+    ): Boolean {
         try {
             val jar = JarMap.open(apk)
             val je = jar.getJarEntry(Const.ANDROID_MANIFEST)
-            val xml = jar.getRawData(je)
+            val xml = AXML(jar.getRawData(je))
 
-            if (!findAndPatch(xml, APP_ID, pkg) ||
-                !findAndPatch(xml, APP_NAME, label))
+            if (!xml.findAndPatch(APP_ID to pkg.toString(), APP_NAME to label.toString()))
                 return false
 
             // Write apk changes
-            jar.getOutputStream(je).write(xml)
-            val keys = Keygen(get())
+            jar.getOutputStream(je).write(xml.bytes)
+            val keys = Keygen(context)
             SignApk.sign(keys.cert, keys.key, jar, FileOutputStream(out))
         } catch (e: Exception) {
             Timber.e(e)
@@ -124,10 +107,10 @@ object PatchAPK {
 
         // Generate a new random package name and signature
         val repack = File(context.cacheDir, "patched.apk")
-        val pkg = genPackageName("com.", APP_ID.length)
+        val pkg = genPackageName()
         Config.keyStoreRaw = ""
 
-        if (!patch(src, repack.path, pkg, label))
+        if (!patch(context, src, repack.path, pkg, label))
             return false
 
         // Install the application

app/src/main/java/com/topjohnwu/magisk/core/utils/AXML.kt

@@ -0,0 +1,132 @@
+package com.topjohnwu.magisk.core.utils
+
+import java.io.ByteArrayOutputStream
+import java.nio.ByteBuffer
+import java.nio.ByteOrder.LITTLE_ENDIAN
+import java.nio.charset.Charset
+import java.util.*
+
+class AXML(b: ByteArray) {
+
+    var bytes = b
+        private set
+
+    companion object {
+        private const val CHUNK_SIZE_OFF = 4
+        private const val STRING_INDICES_OFF = 7 * 4
+        private val UTF_16LE = Charset.forName("UTF-16LE")
+    }
+
+    /**
+     * String pool header:
+     * 0:  0x1C0001
+     * 1:  chunk size
+     * 2:  number of strings
+     * 3:  number of styles (assert as 0)
+     * 4:  flags
+     * 5:  offset to string data
+     * 6:  offset to style data (assert as 0)
+     *
+     * Followed by an array of uint32_t with size = number of strings
+     * Each entry points to an offset into the string data
+     */
+    fun findAndPatch(vararg patterns: Pair<String, String>): Boolean {
+        val buffer = ByteBuffer.wrap(bytes).order(LITTLE_ENDIAN)
+
+        fun findStringPool(): Int {
+            var offset = 8
+            while (offset < bytes.size) {
+                if (buffer.getInt(offset) == 0x1C0001)
+                    return offset
+                offset += buffer.getInt(offset + CHUNK_SIZE_OFF)
+            }
+            return -1
+        }
+
+        var patch = false
+        val start = findStringPool()
+        if (start < 0)
+            return false
+
+        // Read header
+        buffer.position(start + 4)
+        val intBuf = buffer.asIntBuffer()
+        val size = intBuf.get()
+        val count = intBuf.get()
+        intBuf.get()
+        intBuf.get()
+        val dataOff = start + intBuf.get()
+        intBuf.get()
+
+        val strings = ArrayList<String>(count)
+        // Read and patch all strings
+        loop@ for (i in 0 until count) {
+            val off = dataOff + intBuf.get()
+            val len = buffer.getShort(off)
+            val str = String(bytes, off + 2, len * 2, UTF_16LE)
+            for ((from, to) in patterns) {
+                if (str.contains(from)) {
+                    strings.add(str.replace(from, to))
+                    patch = true
+                    continue@loop
+                }
+            }
+            strings.add(str)
+        }
+
+        if (!patch)
+            return false
+
+        // Write everything before string data, will patch values later
+        val baos = RawByteStream()
+        baos.write(bytes, 0, dataOff)
+
+        val strList = IntArray(count)
+        for (i in 0 until count) {
+            strList[i] = baos.size() - dataOff
+            val str = strings[i]
+            baos.write(str.length.toShortBytes())
+            baos.write(str.toByteArray(UTF_16LE))
+            // Null terminate
+            baos.write(0)
+            baos.write(0)
+        }
+        baos.align()
+
+        val sizeDiff = baos.size() - start - size
+        val newBuffer = ByteBuffer.wrap(baos.buf).order(LITTLE_ENDIAN)
+
+        // Patch XML size
+        newBuffer.putInt(CHUNK_SIZE_OFF, buffer.getInt(CHUNK_SIZE_OFF) + sizeDiff)
+        // Patch string pool size
+        newBuffer.putInt(start + CHUNK_SIZE_OFF, size + sizeDiff)
+        // Patch index table
+        newBuffer.position(start + STRING_INDICES_OFF)
+        val newStrList = newBuffer.asIntBuffer()
+        for (idx in strList)
+            newStrList.put(idx)
+
+        // Write the rest of the chunks
+        val nextOff = start + size
+        baos.write(bytes, nextOff, bytes.size - nextOff)
+
+        bytes = baos.toByteArray()
+        return true
+    }
+
+    private fun Int.toShortBytes(): ByteArray {
+        val b = ByteBuffer.allocate(2).order(LITTLE_ENDIAN)
+        b.putShort(this.toShort())
+        return b.array()
+    }
+
+    private class RawByteStream : ByteArrayOutputStream() {
+        val buf get() = buf
+
+        fun align(alignment: Int = 4) {
+            val newCount = (count + alignment - 1) / alignment * alignment
+            for (i in 0 until (newCount - count))
+                write(0)
+        }
+    }
+}

app/src/main/java/com/topjohnwu/magisk/ui/settings/SettingsItems.kt

@@ -11,6 +11,7 @@ import com.topjohnwu.magisk.core.Config
 import com.topjohnwu.magisk.core.Const
 import com.topjohnwu.magisk.core.Info
 import com.topjohnwu.magisk.core.UpdateCheckService
+import com.topjohnwu.magisk.core.tasks.PatchAPK
 import com.topjohnwu.magisk.core.utils.BiometricHelper
 import com.topjohnwu.magisk.core.utils.MediaStoreUtils
 import com.topjohnwu.magisk.core.utils.availableLocales
@@ -88,9 +89,12 @@ object Hide : BaseSettingsItem.Input() {
     var result = "Manager"
         set(value) = set(value, field, { field = it }, BR.result, BR.error)
 
+    val maxLength
+        get() = PatchAPK.MAX_LABEL_LENGTH
+
     @get:Bindable
     val isError
-        get() = result.length > 14 || result.isBlank()
+        get() = result.length > maxLength || result.isBlank()
 
     override fun getView(context: Context) = DialogSettingsAppNameBinding
         .inflate(LayoutInflater.from(context)).also { it.data = this }.root

app/src/main/java/com/topjohnwu/magisk/ui/settings/SettingsViewModel.kt

@@ -19,7 +19,7 @@ import com.topjohnwu.magisk.core.download.Action
 import com.topjohnwu.magisk.core.download.DownloadService
 import com.topjohnwu.magisk.core.download.Subject
 import com.topjohnwu.magisk.core.isRunningAsStub
-import com.topjohnwu.magisk.core.utils.PatchAPK
+import com.topjohnwu.magisk.core.tasks.PatchAPK
 import com.topjohnwu.magisk.data.database.RepoDao
 import com.topjohnwu.magisk.events.AddHomeIconEvent
 import com.topjohnwu.magisk.events.RecreateEvent

app/src/main/res/layout/dialog_settings_app_name.xml

@@ -25,7 +25,7 @@
             android:hint="@string/settings_app_name_hint"
             app:boxStrokeColor="?colorOnSurfaceVariant"
             app:counterEnabled="true"
-            app:counterMaxLength="14"
+            app:counterMaxLength="@{data.maxLength}"
             app:counterOverflowTextColor="?colorError"
             app:error="@{data.error ? @string/settings_app_name_error : @string/empty}"
             app:errorEnabled="true"