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Commit d70160f2 authored by Steven Moreland's avatar Steven Moreland
Browse files

libbinder: vendor binder has a different header 

Right now, on a regular device, libbinder and libbinder.vndk (the
vendor, VNDK variant, of libbinder) are in sync. So, if there is some
error, they will be able to communicate with each other. However, there
is no ABI stability guarantee here. In order to provide an extra layer
of guarantee, we are writing a header to vendor transactions.

This header is not written on system transactions in order to save the
function call, but it may be sane to. Ideally also, it may be sane to
write some hash or similar value instead of a secret code in a specific
case. This would be more flexible.

Bug: 136027762
Test: boot
Change-Id: I664caf6b7082d97e0310e502bf2cd6393e2da9a7
parent fcc8248c

libs/binder/Parcel.cpp

+13 −0
Original line number Diff line number Diff line
@@ -590,6 +590,12 @@ void Parcel::updateWorkSourceRequestHeaderPosition() const { 
    }

}



#ifdef __ANDROID_VNDK__

constexpr int32_t kHeader = B_PACK_CHARS('V', 'N', 'D', 'R');

#else

constexpr int32_t kHeader = B_PACK_CHARS('S', 'Y', 'S', 'T');

#endif



// Write RPC headers.  (previously just the interface token)

status_t Parcel::writeInterfaceToken(const String16& interface)

{
@@ -598,6 +604,7 @@ status_t Parcel::writeInterfaceToken(const String16& interface) 
    updateWorkSourceRequestHeaderPosition();

    writeInt32(threadState->shouldPropagateWorkSource() ?

            threadState->getCallingWorkSourceUid() : IPCThreadState::kUnsetWorkSource);

    writeInt32(kHeader);

    // currently the interface identification token is just its name as a string

    return writeString16(interface);

}
@@ -655,6 +662,12 @@ bool Parcel::enforceInterface(const String16& interface, 
    updateWorkSourceRequestHeaderPosition();

    int32_t workSource = readInt32();

    threadState->setCallingWorkSourceUidWithoutPropagation(workSource);

    // vendor header

    int32_t header = readInt32();

    if (header != kHeader) {

        ALOGE("Expecting header 0x%x but found 0x%x. Mixing copies of libbinder?", kHeader, header);

        return false;

    }

    // Interface descriptor.

    const String16 str(readString16());

    if (str == interface) {