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Commit 5c52b139 authored by Robert Carr's avatar Robert Carr
Browse files

Exclude secure layers from most screenshots taken by the system server. 

In pre-P versions of Android, it was allowed to screenshot secure layers if the
buffer queue producer which was the target of the screenshot was owned by
the system (in this case SurfaceFlinger). This really was a synonym for:
The screen rotation animation was allowed to capture secure layers, but the other
code paths weren't. In O we mistakenly changed this check to always allow the system server
to capture secure layers via the captureScreen path (the captureLayers path used for
TaskSnapshots was unaffected). This can result in data leakage in cases where the
system server takes screenshots on behalf of other parts of the system (e.g. for
the assistant). To mitigate this we provide an explicit switch for the system server
to specify whether it wishes to capture Secure layers. While this is dangerous, I think
it is less dangerous than the previous implicit switch of capturing secure layers based on which
type of BufferQueue was passed in. The flag defaults to not capturing secure layers
and we set it to true in the one place we need it (for the screen rotation animation).
Non privileged clients can still not capture secure layers at all directly.

Test: TransactionTest.cpp#SetFlagsSecureEUidSystem
Bug: 120610669
Change-Id: I9d32c5ac2b005059be9f464859a415167d9ddbd4
parent ccac0718

core/java/android/view/SurfaceControl.java

+25 −2
Original line number Diff line number Diff line
@@ -88,7 +88,8 @@ public final class SurfaceControl implements Parcelable { 
    private static native void nativeDisconnect(long nativeObject);



    private static native GraphicBuffer nativeScreenshot(IBinder displayToken,

            Rect sourceCrop, int width, int height, boolean useIdentityTransform, int rotation);

            Rect sourceCrop, int width, int height, boolean useIdentityTransform, int rotation,

            boolean captureSecureLayers);

    private static native GraphicBuffer nativeCaptureLayers(IBinder layerHandleToken,

            Rect sourceCrop, float frameScale);
@@ -1853,7 +1854,29 @@ public final class SurfaceControl implements Parcelable { 
            throw new IllegalArgumentException("displayToken must not be null");

        }



        return nativeScreenshot(display, sourceCrop, width, height, useIdentityTransform, rotation);

        return nativeScreenshot(display, sourceCrop, width, height, useIdentityTransform, rotation,

                false /* captureSecureLayers */);

    }



    /**

     * Like screenshotToBuffer, but if the caller is AID_SYSTEM, allows

     * for the capture of secure layers. This is used for the screen rotation

     * animation where the system server takes screenshots but does

     * not persist them or allow them to leave the server. However in other

     * cases in the system server, we mostly want to omit secure layers

     * like when we take a screenshot on behalf of the assistant.

     *

     * @hide

     */

    public static GraphicBuffer screenshotToBufferWithSecureLayersUnsafe(IBinder display,

            Rect sourceCrop, int width, int height, boolean useIdentityTransform,

            int rotation) {

        if (display == null) {

            throw new IllegalArgumentException("displayToken must not be null");

        }



        return nativeScreenshot(display, sourceCrop, width, height, useIdentityTransform, rotation,

                true /* captureSecureLayers */);

    }



    private static void rotateCropForSF(Rect crop, int rot) {

core/jni/android_view_SurfaceControl.cpp

+5 −5
Original line number Diff line number Diff line
@@ -205,7 +205,7 @@ static Rect rectFromObj(JNIEnv* env, jobject rectObj) { 


static jobject nativeScreenshot(JNIEnv* env, jclass clazz,

        jobject displayTokenObj, jobject sourceCropObj, jint width, jint height,

        bool useIdentityTransform, int rotation) {

        bool useIdentityTransform, int rotation, bool captureSecureLayers) {

    sp<IBinder> displayToken = ibinderForJavaObject(env, displayTokenObj);

    if (displayToken == NULL) {

        return NULL;
@@ -215,7 +215,7 @@ static jobject nativeScreenshot(JNIEnv* env, jclass clazz, 
    status_t res = ScreenshotClient::capture(displayToken, ui::Dataspace::V0_SRGB,

            ui::PixelFormat::RGBA_8888,

            sourceCrop, width, height,

                                             useIdentityTransform, rotation, &buffer);

            useIdentityTransform, rotation, captureSecureLayers, &buffer);

    if (res != NO_ERROR) {

        return NULL;

    }
@@ -1232,7 +1232,7 @@ static const JNINativeMethod sSurfaceControlMethods[] = { 
            (void*)nativeSetOverrideScalingMode },

    {"nativeGetHandle", "(J)Landroid/os/IBinder;",

            (void*)nativeGetHandle },

    {"nativeScreenshot", "(Landroid/os/IBinder;Landroid/graphics/Rect;IIZI)Landroid/graphics/GraphicBuffer;",

    {"nativeScreenshot", "(Landroid/os/IBinder;Landroid/graphics/Rect;IIZIZ)Landroid/graphics/GraphicBuffer;",

            (void*)nativeScreenshot },

    {"nativeCaptureLayers", "(Landroid/os/IBinder;Landroid/graphics/Rect;F)Landroid/graphics/GraphicBuffer;",

            (void*)nativeCaptureLayers },

services/core/java/com/android/server/display/DisplayManagerService.java

+10 −1
Original line number Diff line number Diff line
@@ -37,7 +37,9 @@ import android.content.pm.ParceledListSlice; 
import android.content.res.Resources;

import android.content.res.TypedArray;

import android.graphics.ColorSpace;

import android.graphics.GraphicBuffer;

import android.graphics.Point;

import android.graphics.Rect;

import android.hardware.SensorManager;

import android.hardware.display.AmbientBrightnessDayStats;

import android.hardware.display.BrightnessChangeEvent;
@@ -1277,7 +1279,14 @@ public final class DisplayManagerService extends SystemService { 
        if (token == null) {

            return false;

        }

        SurfaceControl.screenshot(token, outSurface);

        final GraphicBuffer gb = SurfaceControl.screenshotToBufferWithSecureLayersUnsafe(

                token, new Rect(), 0 /* width */, 0 /* height */, false /* useIdentityTransform */,

                0 /* rotation */);

        try {

            outSurface.attachAndQueueBuffer(gb);

        } catch (RuntimeException e) {

            Slog.w(TAG, "Failed to take screenshot - " + e.getMessage());

        }

        return true;

    }