linux-kernel - Re: controlling mmap()'d vs read/write() pages

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Date:	Fri, 23 Mar 2007 06:21:01 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Dave Hansen <hansendc@...ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org, menage@...gle.com,
	Andrew Morton <akpm@...ux-foundation.org>, xemul@...ru
Subject: Re: controlling mmap()'d vs read/write() pages

Nick Piggin <nickpiggin@...oo.com.au> writes:

>> Would any of them work on a system on which every filesystem was on
>> ramfs, and there was no swap?  If not then they are not memory attacks
>> but I/O attacks.
>>
>> I completely concede that you can DOS the system with I/O if that is
>> not limited as well.
>>
>> My point is that is not a memory problem but a disk I/O problem which is
>> much easier to and cheaper to solve.  Disk I/O is fundamentally a slow
>> path which makes it hard to modify it in a way that negatively affects
>> system performance.
>>
>> I don't think with a memory RSS limit you can DOS the system in a way
>> that is purely about memory.  You have to pick a different kind of DOS
>> attack.
>
> It can be done trivially without performing any IO or swap, yes.

Please give me a rough sketch of how to do so.

Or is this about DOS'ing the system by getting the kernel to allocate
a large number of data structures (struct file, struct inode, or the like)?

Eric
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