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Re: Denial of service attack via libpager
From: |
Richard Braun |
Subject: |
Re: Denial of service attack via libpager |
Date: |
Mon, 29 Aug 2016 00:49:04 +0200 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Sun, Aug 28, 2016 at 12:20:14PM -1000, Brent W. Baccala wrote:
> So, there's several problems here:
>
> 1. libpager can't handle multiple clients
> 2. the kernel can't recover from a failed attempt to get a file's memory
> object
> 3. ext2fs can't cleanly shutdown in this case
>
> I'm continuing to lobby for a multi-client libpager! I can see that it's
> going to raise a lot of locking and concurrency issues, but this program
> demonstrates that we've already got problems with the current scheme. Even
> a simple multi-client libpager should allow shared read-only access, which
> would prevent an unprivileged user from mounting this attack. Root, with
> write access to the files in /bin, could still do it, though.
I'm really not seeing the relation between "multiple clients" and
"multiple threads". Libpager must be able to handle multiple clients
with a single thread, otherwise we don't control scalability and we're
back to where we were before Justus' rework...
And again, I think it's much easier and much more helpful to change
exec and others to _avoid_ mmap, and copy the data in instead,
possibly (and in this case probably) with zero-copy.
Finally, I fail to see how making libpager handle multiple clients
will solve that issue. The only client should be the local kernel,
right ?
--
Richard Braun
- Denial of service attack via libpager, Brent W. Baccala, 2016/08/28
- Re: Denial of service attack via libpager,
Richard Braun <=
- Re: Denial of service attack via libpager, Brent W. Baccala, 2016/08/28
- Re: Denial of service attack via libpager, Richard Braun, 2016/08/29
- Re: Denial of service attack via libpager, Richard Braun, 2016/08/29
- Re: Denial of service attack via libpager, Richard Braun, 2016/08/29
- Re: Denial of service attack via libpager, Brent W. Baccala, 2016/08/29
- Re: Denial of service attack via libpager, Richard Braun, 2016/08/30