Re: [PATCH] selinux-testsuite: Update binder for kernel 5.4 support

[Stephen Smalley <sds@tycho.nsa.gov>]

On 10/8/19 5:43 PM, Paul Moore wrote:
> On Mon, Oct 7, 2019 at 12:35 PM Richard Haines
> <richard_c_haines@btinternet.com> wrote:
>> On Mon, 2019-10-07 at 16:17 +0100, Richard Haines wrote:
>>> On Mon, 2019-10-07 at 10:28 -0400, Stephen Smalley wrote:
>>>> On 10/6/19 4:51 AM, Richard Haines wrote:
>>>>> Kernel 5.4 commit ca2864c6e8965c37df97f11e6f99e83e09806b1c
>>>>> ("binder: Add
>>>>> default binder devices through binderfs when configured"),
>>>>> changed
>>>>> the way
>>>>> the binder device is initialised and no longer automatically
>>>>> generates
>>>>> /dev/binder when CONFIG_ANDROID_BINDERFS=y.
>>>>
>>>> This seems like a userspace ABI break, no?  Same kernel config
>>>> before
>>>> and after this commit yields different behavior for
>>>> /dev/binder.  I
>>>> suppose one might argue that one would only enable
>>>> CONFIG_ANDROID_BINDERFS if one wanted to use it instead of
>>>> /dev/binder
>>>> but the original commit that introduced binderfs specifically said
>>>> that
>>>> backward compatibility was preserved.
>>> I'll need to check this further, but from what I've seen so far, is
>>> that the /dev/binder is not available until you mount binderfs etc.
>>> that's why Paul had the failure on 5.4 as before then is was
>>> available
>>> when the binder driver first initialised.
>>
>> To confirm tests using kernel 5.4-rc1
>>
>> Test 1 config:
>> CONFIG_ANDROID=y
>> CONFIG_ANDROID_BINDER_IPC=y
>> CONFIG_ANDROID_BINDERFS=y
>> CONFIG_ANDROID_BINDER_DEVICES="binder"
>>
>> On boot no /dev/binder
>>
>> To get this you have to:
>> mkdir /dev/binderfs 2>/dev/null
>> mount -t binder binder /dev/binderfs -o
>> context=system_u:object_r:device_t:s0 2>/dev/null
>>
>> You then have devs:
>> binder and binder-control
>>
>> Test 2 config:
>> CONFIG_ANDROID=y
>> CONFIG_ANDROID_BINDER_IPC=y
>> # CONFIG_ANDROID_BINDERFS is not set
>> CONFIG_ANDROID_BINDER_DEVICES="binder"
>>
>> On boot you have /dev/binder
> 
> Disabling binderfs during build is probably not the smart thing to do
> considering where the world is at with namespaces/containers, whatever
> we do we should make sure the tests work with
> CONFIG_ANDROID_BINDERFS=y.

Yes, I think the question is just whether we want to have the tests use 
binderfs for kernel >= 5.0 (i.e. the point at which binderfs was first 
introduced) or for kernel >= 5.4 (i.e. the point at which binderfs usage 
became mandatory if you enable it in your config because /dev/binder is 
no longer automatically created).  I'm fine either way.