[RFC][PATCH] net/bpfilter: Remove this broken and apparently unmantained

[Tetsuo Handa]

Forwarding to LSM-ML again. Any comments?

On 2020/06/24 15:39, Alexei Starovoitov wrote:
> On Wed, Jun 24, 2020 at 01:58:33PM +0900, Tetsuo Handa wrote:
>> On 2020/06/24 13:00, Alexei Starovoitov wrote:
>>>> However, regarding usermode_blob, although the byte array (which contains code / data)
>>>> might be initially loaded from the kernel space (which is protected), that byte array
>>>> is no longer protected (e.g. SIGKILL, strace()) when executed because they are placed
>>>> in the user address space. Thus, LSM modules (including pathname based security) want
>>>> to control how that byte array can behave.
>>>
>>> It's privileged memory regardless. root can poke into kernel or any process memory.
>>
>> LSM is there to restrict processes running as "root".
> 
> hmm. do you really mean that it's possible for an LSM to restrict CAP_SYS_ADMIN effectively?
> LSM can certainly provide extra level of foolproof-ness against accidental
> mistakes, but it's not a security boundary.
> 
>> Your "root can poke into kernel or any process memory." response is out of step with the times.
>>
>> Initial byte array used for usermode blob might be protected because of "part of .rodata or
>> .init.rodata of kernel module", but that byte array after started in userspace is no longer
>> protected. 
>>
>> I don't trust such byte array as "part of kernel module", and I'm asking you how
>> such byte array does not interfere (or be interfered by) the rest of the system.
> 
> Could you please explain the attack vector that you see in such scenario?
> How elf binaries embedded in the kernel modules different from pid 1?
> If anything can peek into their memory the system is compromised.
> Say, there are no user blobs in kernel modules. How pid 1 memory is different
> from all the JITed images? How is it different for all memory regions shared
> between kernel and user processes?
> I see an opportunity for an LSM to provide a protection against non-security
> bugs when system is running trusted apps, but not when arbitrary code can
> execute under root.
>