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

[Tetsuo Handa]

On 2020/06/24 23:26, Alexei Starovoitov wrote:
> On Wed, Jun 24, 2020 at 5:17 AM Eric W. Biederman <ebiederm at xmission.com> wrote:
>>
>> Alexei Starovoitov <alexei.starovoitov at gmail.com> writes:
>>
>>> On Tue, Jun 23, 2020 at 01:53:48PM -0500, Eric W. Biederman wrote:
>>
>>> There is no refcnt bug. It was a user error on tomoyo side.
>>> fork_blob() works as expected.
>>
>> Nope.  I have independently confirmed it myself.
> 
> I guess you've tried Tetsuo's fork_blob("#!/bin/true") kernel module ?
> yes. that fails. It never meant to be used for this.
> With elf blob it works, but breaks if there are rejections
> in things like security_bprm_creds_for_exec().
> In my mind that path was 'must succeed or kernel module is toast'.
> Like passing NULL into a function that doesn't check for it.
> Working on a fix for that since Tetsuo cares.
> 

What is unhappy for pathname based LSMs is that fork_usermode_blob() creates
a file with empty filename. I can imagine that somebody would start abusing
fork_usermode_blob() as an interface for starting programs like modprobe, hotplug,
udevd and sshd. When such situation happened, how fork_usermode_blob() provides
information for identifying the intent of such execve() requests?

fork_usermode_blob() might also be an unhappy behavior for inode based LSMs (like
SELinux and Smack) because it seems that fork_usermode_blob() can't have a chance
to associate appropriate security labels based on the content of the byte array
because files are created on-demand. Is fork_usermode_blob() friendly to inode
based LSMs?