From 540d579f3079b1796414f12118632c6adc9387e3 Mon Sep 17 00:00:00 2001 From: Tri Vo Date: Mon, 8 Apr 2019 10:41:10 -0700 Subject: Reland 'Check /dev/binder access before calling defaultServiceManager()' Vendor processes do not have access to /dev/binder. Calling defaultServiceManager() without RW permission will crash the process with error message "Binder driver could not be opened. Terminating." Normally, VNDK version of libcutils.so would not have the codepath of ashmemd. However, on non-VNDK this codepath is exercised. We check if the current process has permissions to /dev/binder before calling defaultServiceManager() to avoid crashing. The calling code in libcutils.so handles inability to connect ashmemd correctly. It will fall back to opening /dev/ashmem directly. Vendor code should already have permissions for that. This SELinux denial shows which permissions need to be checked for: avc: denied { read write } for name="binder" dev="tmpfs" ino=5570 scontext=u:r:hal_sensors_default:s0 tcontext=u:object_r:binder_device:s0 tclass=chr_file permissive=0 Note that the problem only manifests on non-VNDK devices. Bug: 129073672 Test: ashmemd_test Test: VtsHalSensorsV1_0TargetTest --gtest_filter=SensorsHidlTest.AccelerometerAshmemDirectReportOperationNormal Test: atest CtsOsTestCases:android.os.cts.SeccompTest#testIsolatedServicePolicy Change-Id: I23bef7986298811ce2bd84c3fdc9c9e22837c368 Merged-In: I23bef7986298811ce2bd84c3fdc9c9e22837c368 (cherry picked from commit febe203d835f89eede3979e44bb80b2cda523047) --- ashmemd_client.cpp | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/ashmemd_client.cpp b/ashmemd_client.cpp index 3380209..a9041a0 100644 --- a/ashmemd_client.cpp +++ b/ashmemd_client.cpp @@ -17,6 +17,7 @@ #include #include #include +#include using android::IBinder; using android::IServiceManager; @@ -27,7 +28,25 @@ using android::os::ParcelFileDescriptor; namespace android { namespace ashmemd { +static bool checkBinderAccess() { + // Isolated apps are potentially subject to seccomp policy that restricts use of access() + // (b/129483782). However, apps always have access to binder, so return true. + auto uid = getuid() % AID_USER; + if (AID_ISOLATED_START <= uid && uid <= AID_ISOLATED_END) { + return true; + } + if (access("/dev/binder", R_OK | W_OK) == 0) { + return true; + } + return false; +} + sp getAshmemService() { + // Calls to defaultServiceManager() crash the process if it doesn't have appropriate + // binder permissions. Check these permissions proactively. + if (!checkBinderAccess()) { + return nullptr; + } sp sm = android::defaultServiceManager(); sp binder = sm->checkService(String16("ashmem_device_service")); return interface_cast(binder); -- cgit v1.2.3