From: Christoph Rohland <cr@sap.com>
To: Pavel Roskin <proski@gnu.org>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: DoS using tmpfs
Date: 13 Jun 2001 09:04:51 +0200 [thread overview]
Message-ID: <m3vgm06ess.fsf@linux.local> (raw)
In-Reply-To: <Pine.LNX.4.33.0106081755220.1324-100000@vesta.nine.com>
In-Reply-To: Pavel Roskin's message of "Fri, 8 Jun 2001 18:42:40 -0400 (EDT)"
Hi Pavel,
On Fri, 8 Jun 2001, Pavel Roskin wrote:
> Hello!
>
> It appears that a system with tmpfs mounted with the default (!!!)
> parameters can be used by ordinary users to make the system
> non-functional.
...
> 1) tmpfs, as opposed to ramfs doesn't limit the usage by
> default. It's not a good default for a filesystem designed for
> temporary files.
Yes, use the size parameter. And no, ramfs has no resource limits in
the stock kernel at all. In -ac it limits to half the size of the
physical RAM unconditionally. But that's not useful for tmpfs simce
this uses swap also. So it is the admins task to add a size
parameter. I would love to add a size paramater in percent of virtual
memory but this would need some changes in the swapon/off coding.
> 2) Not delivering SIGINT to processes is probably not the best
> behavior if the memory if low. However, one could argue that some
> processes would use even more resources if they get control with
> SIGINT.
>
> 3) All swap in the system was exhausted and yet tmpfs didn't return
> ENOSPC to "dd".
That the kernel locks up is IMHO a mm fault. tmpfs allocates its pages
with GFP_USER and will return an error if this fails. Apparently it
never fails but locks up.
Greetings
Christoph
prev parent reply other threads:[~2001-06-13 7:05 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-06-08 22:42 DoS using tmpfs Pavel Roskin
2001-06-13 7:04 ` Christoph Rohland [this message]
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