Re: [PATCH] nextfd(2)

[Kyle Moffett]

On Sun, Apr 1, 2012 at 15:03, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 04/01/2012 05:57 AM, Alexey Dobriyan wrote:
>> * /proc/self/fd is unreliable:
>> Â proc may be unconfigured or not mounted at expected place.
>> Â Looking at /proc/self/fd requires opening directory
>> Â which may not be available due to malicious rlimit drop or ENOMEM situations.
>> Â Not opening directory is equivalent to dumb close(2) loop except slower.
>
> This is really the motivation for this... the real question is how much
> functionality is actually available in the system without /proc mounted,
> and in particular if this particular subcase is worth optimizing ...
> after all, if someone is maliciously setting rlimit, we can just abort
> (if someone can set an rlimit they can also force an abort) or revert to
> the slow path.

Well, I imagine one typical usecase for closing all FDs is for
security isolation purposes (EG: chroot()+etc), and in a great deal of
chroot environments you don't have /proc available.  In particular
/proc has been a source of a lot of privilege escalations in the past,
so avoiding mounting it in a chroot is good security policy if
possible.

Cheers,
Kyle Moffett
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