Messages in this thread | | | Subject | Re: Algoritmic Complexity Attacks and 2.4.20 the dcache code | From | Scott A Crosby <> | Date | 29 May 2003 23:42:09 -0500 |
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On Fri, 30 May 2003 06:02:18 +0200 (CEST), Ingo Molnar <mingo@elte.hu> writes:
> On 29 May 2003, Scott A Crosby wrote: > > > I have confirmed via an actual attack that it is possible to force the > > dcache to experience a 200x performance degradation if the attacker can > > control filenames. On a P4-1.8ghz, the time to list a directory of > > 10,000 files is 18 seconds instead of .1 seconds. > > are you sure this is a big issue? Kernel 2.0 (maybe even 2.2) lists 10,000 > files at roughly the same speed (18 seconds) without any attack pattern > used for filenames - still it's a kernel being used.
No. Its not that severe, but it does exist, and it is noticable even with a quarter that number of files. I did it because it was an interesting illustrative example, and it only took 30 seconds or so of coding to put the hash function into generator generating program.
> So it would take a really specialized attack to keep the dcache size > at the critical level and trigger the slowdown.
Yup. It is probably a very unusual configuration, but that doesn't mean that somebody won't experience it. :)
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