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Improve EncryptedProxyFileDescriptor.isSupported

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This commit is contained in:
Greyson Parrelli
2026-08-05 15:01:57 -04:00
parent a9898bec71
commit b594920d36
2 changed files with 83 additions and 24 deletions
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core/util/src/main/java/org/signal/core/util/EncryptedProxyFileDescriptor.kt
+58 -21
View File
@@ -50,7 +50,13 @@ class EncryptedProxyFileDescriptor private constructor(
private const val DIRECTORY = "encrypted-proxy-fd"
private const val SELF_TEST_DEBUG_NAME = "self-test"
private const val SELF_TEST_SIZE = 4096
private const val SELF_TEST_HEADER_SIZE = 28
private const val SELF_TEST_LARGE_WRITE_SIZE = 512 * 1024
private const val SELF_TEST_FOOTER_OFFSET = SELF_TEST_HEADER_SIZE + SELF_TEST_LARGE_WRITE_SIZE
private const val SELF_TEST_FOOTER_SIZE = 16
private const val SELF_TEST_SIZE = SELF_TEST_FOOTER_OFFSET + SELF_TEST_FOOTER_SIZE
private const val SELF_TEST_PATCH_OFFSET = 8
private const val SELF_TEST_PATCH_SIZE = 8
private const val KEY_SIZE = 32
private const val BLOCK_SIZE = 16
@@ -82,6 +88,19 @@ class EncryptedProxyFileDescriptor private constructor(
return result
}
/**
* Retires proxy file descriptors for the remainder of the process, so that callers fall back to whatever
* they use when they're unavailable. For failures that only surface once a descriptor is in real use, which
* the self-test cannot be relied upon to predict.
*/
@JvmStatic
fun markUnsupported() {
if (cachedSelfTestResult != false) {
Log.w(TAG, "Marking proxy file descriptors as unsupported.")
}
cachedSelfTestResult = false
}
/**
* Creates a new descriptor whose backing file lives in the app's cache directory, or null if one
* could not be opened.
@@ -90,6 +109,10 @@ class EncryptedProxyFileDescriptor private constructor(
*/
@JvmStatic
fun create(context: Context, debugName: String): EncryptedProxyFileDescriptor? {
if (cachedSelfTestResult == false) {
return null
}
val storageManager = context.getSystemService(StorageManager::class.java)
if (storageManager == null) {
Log.w(TAG, "StorageManager is unavailable.")
@@ -163,8 +186,8 @@ class EncryptedProxyFileDescriptor private constructor(
}
/**
* Verifies that data written through a proxy descriptor at various offsets reads back
* intact, and that only ciphertext lands in the backing file.
* Verifies that data written through a proxy descriptor reads back intact, and that only ciphertext
* lands in the backing file. Mirrors MP4 muxer write pattern.
*/
private fun selfTest(context: Context): Boolean {
val descriptor = create(context, SELF_TEST_DEBUG_NAME)
@@ -174,28 +197,35 @@ class EncryptedProxyFileDescriptor private constructor(
}
return descriptor.use { proxy ->
val fd = proxy.fileDescriptor
val random = SecureRandom()
val expected = ByteArray(SELF_TEST_SIZE).also { random.nextBytes(it) }
if (!pwriteFully(proxy.fileDescriptor, expected, 0, expected.size, 0)) {
Log.w(TAG, "Self-test: short write.")
if (!pwriteExact(fd, "header", expected, 0, SELF_TEST_HEADER_SIZE, 0)) {
return@use false
}
val overwrite = ByteArray(100).also { random.nextBytes(it) }
System.arraycopy(overwrite, 0, expected, 1000, overwrite.size)
if (!pwriteFully(proxy.fileDescriptor, overwrite, 0, overwrite.size, 1000)) {
Log.w(TAG, "Self-test: short overwrite.")
if (!pwriteExact(fd, "reservation", expected, SELF_TEST_HEADER_SIZE, SELF_TEST_LARGE_WRITE_SIZE, SELF_TEST_HEADER_SIZE.toLong())) {
return@use false
}
if (Os.fstat(proxy.fileDescriptor).st_size != expected.size.toLong()) {
if (!pwriteExact(fd, "footer", expected, SELF_TEST_FOOTER_OFFSET, SELF_TEST_FOOTER_SIZE, SELF_TEST_FOOTER_OFFSET.toLong())) {
return@use false
}
val patch = ByteArray(SELF_TEST_PATCH_SIZE).also { random.nextBytes(it) }
System.arraycopy(patch, 0, expected, SELF_TEST_PATCH_OFFSET, patch.size)
if (!pwriteExact(fd, "patch", patch, 0, patch.size, SELF_TEST_PATCH_OFFSET.toLong())) {
return@use false
}
if (Os.fstat(fd).st_size != SELF_TEST_SIZE.toLong()) {
Log.w(TAG, "Self-test: unexpected file size.")
return@use false
}
val actual = ByteArray(expected.size)
if (!preadFully(proxy.fileDescriptor, actual, 0, actual.size, 0)) {
val actual = ByteArray(SELF_TEST_SIZE)
if (!preadFully(fd, actual, 0, actual.size, 0)) {
Log.w(TAG, "Self-test: short read.")
return@use false
}
@@ -206,7 +236,7 @@ class EncryptedProxyFileDescriptor private constructor(
}
val onDisk = proxy.backingFile.readBytes()
if (onDisk.size != expected.size || onDisk.contentEquals(expected)) {
if (onDisk.size != SELF_TEST_SIZE || onDisk.contentEquals(expected)) {
Log.w(TAG, "Self-test: backing file does not look encrypted.")
return@use false
}
@@ -215,15 +245,22 @@ class EncryptedProxyFileDescriptor private constructor(
}
}
private fun pwriteFully(fd: FileDescriptor, data: ByteArray, byteOffset: Int, byteCount: Int, fileOffset: Long): Boolean {
var written = 0
while (written < byteCount) {
val result = Os.pwrite(fd, data, byteOffset + written, byteCount - written, fileOffset + written)
if (result <= 0) {
return false
}
written += result
/**
* A single [Os.pwrite] that has to transfer everything it was handed.
*/
private fun pwriteExact(fd: FileDescriptor, label: String, data: ByteArray, byteOffset: Int, byteCount: Int, fileOffset: Long): Boolean {
val written = try {
Os.pwrite(fd, data, byteOffset, byteCount, fileOffset)
} catch (e: ErrnoException) {
Log.w(TAG, "Self-test: $label write failed.", e)
return false
}
if (written != byteCount) {
Log.w(TAG, "Self-test: $label write was short. Wanted $byteCount, wrote $written.")
return false
}
return true
}
feature/media-send/src/main/java/org/signal/mediasend/screens/capture/CameraXFragment.kt
+25 -3
View File
@@ -379,6 +379,7 @@ class ActiveRecording(val parcelFd: ParcelFileDescriptor, val maxDurationSeconds
class VideoFileDescriptor(val context: Context) {
private var videoFileDescriptor: SeekableFileDescriptor? = null
private var usingEncryptedDisk: Boolean = false
/**
* Creates the descriptor to record into, reporting the cap that goes with whichever descriptor was actually
@@ -396,6 +397,7 @@ class VideoFileDescriptor(val context: Context) {
val encrypted = CameraXUtil.createEncryptedDiskVideoFileDescriptor(context)
if (encrypted != null) {
videoFileDescriptor = encrypted
usingEncryptedDisk = true
return ActiveRecording(encrypted.parcelFd, config.maxDurationSeconds)
}
Log.w(TAG, "Failed to create encrypted disk file descriptor, falling back to memory")
@@ -411,6 +413,20 @@ class VideoFileDescriptor(val context: Context) {
}
}
/**
* The recording never produced a file. A disk-backed descriptor that fails this late fails the same way on
* every retry, so retire it for the rest of the process and let the next recording take the RAM-backed one
* and its shorter cap.
*/
fun onRecordingFailed() {
if (usingEncryptedDisk && Build.VERSION.SDK_INT >= 26) {
Log.w(TAG, "Recording failed on an encrypted disk descriptor. Falling back to memory from here on.")
EncryptedProxyFileDescriptor.markUnsupported()
}
destroy()
}
/**
* Hands the recorded descriptor to the consumer, which becomes responsible for closing it. The copy on the
* consuming side runs asynchronously and can outlive this screen, so ownership has to travel with it.
@@ -418,6 +434,7 @@ class VideoFileDescriptor(val context: Context) {
fun releaseForReading(): SeekableFileDescriptor? {
val descriptor = videoFileDescriptor ?: return null
videoFileDescriptor = null
usingEncryptedDisk = false
return try {
Os.lseek(descriptor.fileDescriptor, 0, OsConstants.SEEK_SET)
@@ -432,6 +449,7 @@ class VideoFileDescriptor(val context: Context) {
fun destroy() {
videoFileDescriptor?.closeQuietly()
videoFileDescriptor = null
usingEncryptedDisk = false
}
}
@@ -594,7 +612,8 @@ fun CameraXScreen(
activeRecordingMaxDurationMs = it.maxDurationSeconds * 1000L
}
},
releaseVideoFileDescriptor = { videoFileDescriptor.releaseForReading() }
releaseVideoFileDescriptor = { videoFileDescriptor.releaseForReading() },
onVideoCaptureFailed = { videoFileDescriptor.onRecordingFailed() }
)
},
stringResources = StringResources(
@@ -691,7 +710,8 @@ private fun handleHudEvent(
isVideoEnabled: Boolean,
onRequestMicPermission: () -> Unit,
createVideoFileDescriptor: () -> ActiveRecording?,
releaseVideoFileDescriptor: () -> SeekableFileDescriptor?
releaseVideoFileDescriptor: () -> SeekableFileDescriptor?,
onVideoCaptureFailed: () -> Unit
) {
when (event) {
is StandardCameraHudEvents.PhotoCaptureTriggered -> {
@@ -711,7 +731,7 @@ private fun handleHudEvent(
context = context,
output = VideoOutput.FileDescriptorOutput(recording.parcelFd),
onVideoCaptured = { result ->
handleVideoCaptured(result, releaseVideoFileDescriptor, onEvent)
handleVideoCaptured(result, releaseVideoFileDescriptor, onVideoCaptureFailed, onEvent)
}
)
} else {
@@ -766,6 +786,7 @@ private fun handlePhotoCaptured(bitmap: Bitmap, onEvent: (CameraXScreenEvents) -
private fun handleVideoCaptured(
result: VideoCaptureResult,
releaseVideoFileDescriptor: () -> SeekableFileDescriptor?,
onVideoCaptureFailed: () -> Unit,
onEvent: (CameraXScreenEvents) -> Unit
) {
when (result) {
@@ -780,6 +801,7 @@ private fun handleVideoCaptured(
is VideoCaptureResult.Error -> {
Log.w(TAG, "Video capture failed: ${result.message}", result.throwable)
onVideoCaptureFailed()
onEvent(CameraXScreenEvents.VideoCaptureError)
}
}