Re: [PATCH] unix: properly account for FDs passed over unix sockets

From	One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Newsgroups	linux.kernel
Subject	Re: [PATCH] unix: properly account for FDs passed over unix sockets
Date	2015-12-30 14:20 +0100
Message-ID	<qLoPv-76p-1@gated-at.bofh.it> (permalink)
References	<qKGOu-3bZ-17@gated-at.bofh.it> <qL3L3-1P0-13@gated-at.bofh.it> <qL9dM-5lK-15@gated-at.bofh.it> <qLkLU-4kl-11@gated-at.bofh.it> <qLn73-5Wu-7@gated-at.bofh.it>
Organization	Intel Corporation

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> > Another idea would be to add the amount of memory used to manage the fds 
> > to sock_rmem/wmem but I don't see any advantages or disadvantages.
> 
> Compared to the impact of the pending data in pipes themselves in flight,
> this would remain fairly minimal.

The true size of the memory pinned by a file handle cannot be determined
by the socket layer anyway. If the handle is for a device it may be
pinning lots of memory in the device driver. It's up to the rest of the
system to manage and contain those resource allocations correctly which a
fair bit of the code (except graphics) does properly.

The resource counting does create the reverse problem that user A running
a program written by hostile user B may find it takes all their resources,
stuffs them down an AF_UNIX socket and passes the last reference to the
socket via a setuid app somewhere where the user can't get it back.

For an end user case that's pretty irrelevant - you run hostile user B's
app then you already lost. For a service it's an interesting attack vector
but not one I can see any obvious ways to exploit because (with the
possible exception of dbus) services simply don't pass file handles down
sockets to untrusted targets.

Alan
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Thread

[PATCH] unix: properly account for FDs passed over unix sockets Willy Tarreau <w@1wt.eu> - 2015-12-28 15:20 +0100
  Re: [PATCH] unix: properly account for FDs passed over unix sockets Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-12-29 15:40 +0100
  Re: [PATCH] unix: properly account for FDs passed over unix sockets Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-12-29 15:50 +0100
    Re: [PATCH] unix: properly account for FDs passed over unix sockets Willy Tarreau <w@1wt.eu> - 2015-12-29 21:40 +0100
      Re: [PATCH] unix: properly account for FDs passed over unix sockets Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-12-30 10:00 +0100
        Re: [PATCH] unix: properly account for FDs passed over unix sockets Willy Tarreau <w@1wt.eu> - 2015-12-30 12:30 +0100
          Re: [PATCH] unix: properly account for FDs passed over unix sockets One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2015-12-30 14:20 +0100
          Re: [PATCH] unix: properly account for FDs passed over unix sockets Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-12-31 07:10 +0100
            Re: [PATCH] unix: properly account for FDs passed over unix sockets Willy Tarreau <w@1wt.eu> - 2015-12-31 08:20 +0100
              Re: [PATCH] unix: properly account for FDs passed over unix sockets One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2015-12-31 11:40 +0100

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