linux-kernel - Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1

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Date:   Tue, 7 Apr 2020 22:29:42 +0200
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1



On 4/7/20 9:50 PM, Linus Torvalds wrote:
> On Mon, Apr 6, 2020 at 3:20 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>>
>> But fundamentally the only reason we need this information stable
>> before the point of no return is so that we can return a nice error
>> code to the process calling exec.  Instead of terminating the
>> process with SIGSEGV.
> 
> I'd suggest doing it the other way around instead: let the thread that
> does the security_setprocattr() die, since execve() is terminating
> other threads anyway.
> 
> And the easy way to do that is to just make the rule be that anybody
> who waits for this thing for write needs to use a killable wait.
> 
> So if the execve() got started earlier, and already took the cred lock
> (whatever we'll call it) for reading, then zap_other_threads() will
> take care of another thread doing setprocattr().
> 
> That sounds like a really simple model, no?
> 

Maybe, actually I considered this, but I was anxious that making something
that is so far not killable suddenly killable might break other things.

But I am a wimp :-)


Bernd.




>                 Linus
>