linux-kernel - Re: proc_flush

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Date:   Tue, 19 Dec 2017 12:27:30 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Dave Jones <davej@...emonkey.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: proc_flush_task oops

Dave Jones <davej@...emonkey.org.uk> writes:

> On Mon, Dec 18, 2017 at 03:50:52PM -0800, Linus Torvalds wrote:
>
>  > But I don't see what would have changed in this area recently.
>  > 
>  > Do you end up saving the seeds that cause crashes? Is this
>  > reproducible? (Other than seeing it twoce, of course)
>
> Only clue so far, is every time I'm able to trigger it, the last thing
> the child process that triggers it did, was an execveat.

Is there any chance the excveat might be called from a child thread?

That switching pids between tasks of a process during exec can get a
little bit tricky.

> Telling it to just fuzz execveat doesn't instantly trigger it, so it
> must be a combination of some other syscall. I'll leave a script running
> overnight to see if I can binary search the other syscalls in
> combination with it.

Could we have a buggy syscall that is stomping something?

> One other thing: I said this was rc4, but it was actually rc4 + all the
> x86 stuff from today.  There's enough creepy stuff in that pile, that
> I'll try with just plain rc4 tomorrow too.

Eric