From: Alex Elder <aelder@sgi.com>
To: Arkadiusz Miskiewicz <arekm@maven.pl>
Cc: xfs@oss.sgi.com
Subject: Re: xfs_metadump in never ending loop
Date: Mon, 04 Oct 2010 09:21:11 -0500 [thread overview]
Message-ID: <1286202071.2120.8.camel@doink> (raw)
In-Reply-To: <1286150266.4344.9.camel@doink>
On Sun, 2010-10-03 at 18:57 -0500, Alex Elder wrote:
> On Fri, 2010-10-01 at 21:36 +0200, Arkadiusz Miskiewicz wrote:
> > generate_obfuscated_name() in metadump.c can go into
> > never ending loop for some file names. Reproducer below.
>
> The reason it hangs is that the algorithm for computing
> a name with the same hash value as the name is stuck with
> a portion of the hash whose only possible result includes
> the string "/" in it.
I understand this problem, and have a solution. But
before sending out the code I want to write up an
explanation of the problem, including the effect of
the hash and why the existing algorithm has problems.
Stay tuned.
-Alex
> The hash for the file "R\323\257NE" is 0x3ab4b3740.
>
> One step in the algorithm is this:
> newname[namelen - 3] = (newhash >> 14) & 0x7f;
> if (is_invalid_char(newname[namelen - 3]))
> continue;
>
> But the result of that is 0x2f, which is the '/'
> character, which is illegal. So this algorithm
> will try again indefinitely, never finding a file
> name with a matching hash.
>
> I am looking into this a bit more. Will report back
> later, probably tomorrow.
>
> -Alex
>
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prev parent reply other threads:[~2010-10-04 14:20 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-01 19:36 xfs_metadump in never ending loop Arkadiusz Miskiewicz
2010-10-03 23:57 ` Alex Elder
2010-10-04 14:21 ` Alex Elder [this message]
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