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Commit 94fb5b0b authored by Luis Hector Chavez's avatar Luis Hector Chavez
Browse files

init: Drop inheritable capabilities when switching uids 

This change explicitly drops all inheritable capabilities (and, by
extension, ambient capabilities) when there are no explicit capabilities
being set by a service and the user is changed. This prevents Android
running in a container from accidentally granting extra capabilities to
services.

Bug: 69320306
Test: aosp_sailfish still boots
Test: sailfish:/ $ grep Cap /proc/`pidof android.hardware.audio@2.0-service`/status
      CapInh: 0000000000000000
      CapPrm: 0000000000000000
      CapEff: 0000000000000000
      CapBnd: 0000003fffffffff
      CapAmb: 0000000000000000
Test: sailfish:/ $ grep Cap /proc/`pidof logd`/status
      CapInh: 0000000000000000
      CapPrm: 0000000440000000
      CapEff: 0000000440000000
      CapBnd: 0000003fffffffff
      CapAmb: 0000000000000000
Test: Android in Chrome OS still boots
Test: localhost ~ # grep Cap /proc/`pidof android.hardware.audio@2.0-service`/status
      CapInh: 0000000000000000
      CapPrm: 0000000000000000
      CapEff: 0000000000000000
      CapBnd: 000000006daefdff
      CapAmb: 0000000000000000
Test: localhost ~ # grep Cap /proc/`pidof logd`/status
      CapInh: 0000000000000000
      CapPrm: 0000000040000000
      CapEff: 0000000040000000
      CapBnd: 000000006daefdff
      CapAmb: 0000000000000000

Change-Id: I9218f2e27ff4fb4d91d50f9a98c0fdb4e272952c
parent 37eb97d9

init/capabilities.cpp

+13 −0
Original line number Diff line number Diff line
@@ -194,5 +194,18 @@ bool SetCapsForExec(const CapSet& to_keep) { 
    return SetAmbientCaps(to_keep);

}



bool DropInheritableCaps() {

    ScopedCaps caps(cap_get_proc());

    if (cap_clear_flag(caps.get(), CAP_INHERITABLE) == -1) {

        PLOG(ERROR) << "cap_clear_flag(INHERITABLE) failed";

        return false;

    }

    if (cap_set_proc(caps.get()) != 0) {

        PLOG(ERROR) << "cap_set_proc() failed";

        return false;

    }

    return true;

}



}  // namespace init

}  // namespace android

init/capabilities.h

+1 −0
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ int LookupCap(const std::string& cap_name); 
bool CapAmbientSupported();

unsigned int GetLastValidCap();

bool SetCapsForExec(const CapSet& to_keep);

bool DropInheritableCaps();



}  // namespace init

}  // namespace android

init/service.cpp

+5 −0
Original line number Diff line number Diff line
@@ -291,6 +291,11 @@ void Service::SetProcessAttributes() { 
        if (!SetCapsForExec(capabilities_)) {

            LOG(FATAL) << "cannot set capabilities for " << name_;

        }

    } else if (uid_) {

        // Inheritable caps can be non-zero when running in a container.

        if (!DropInheritableCaps()) {

            LOG(FATAL) << "cannot drop inheritable caps for " << name_;

        }

    }

}