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Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in place of MD5

From Hannes Frederic Sowa <hannes@stressinduktion.org>
Newsgroups linux.kernel
Subject Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in place of MD5
Date 2016-12-22 19:10 +0100
Message-ID <sRfYu-4o0-15@gated-at.bofh.it> (permalink)
References (5 earlier) <sR1C9-3eC-5@gated-at.bofh.it> <sR4qm-5dV-33@gated-at.bofh.it> <sRaYO-17u-35@gated-at.bofh.it> <sRbrP-1xS-1@gated-at.bofh.it> <sRdWG-2Tv-31@gated-at.bofh.it>
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On 22.12.2016 16:54, Theodore Ts'o wrote:
> On Thu, Dec 22, 2016 at 02:10:33PM +0100, Jason A. Donenfeld wrote:
>> On Thu, Dec 22, 2016 at 1:47 PM, Hannes Frederic Sowa
>> <hannes@stressinduktion.org> wrote:
>>> following up on what appears to be a random subject: ;)
>>>
>>> IIRC, ext4 code by default still uses half_md4 for hashing of filenames
>>> in the htree. siphash seems to fit this use case pretty good.
>>
>> I saw this too. I'll try to address it in v8 of this series.
> 
> This is a separate issue, and this series is getting a bit too
> complex.  So I'd suggest pushing this off to a separate change.
> 
> Changing the htree hash algorithm is an on-disk format change, and so
> we couldn't roll it out until e2fsprogs gets updated and rolled out
> pretty broadley.  In fact George sent me patches to add siphash as a
> hash algorithm for htree a while back (for both the kernel and
> e2fsprogs), but I never got around to testing and applying them,
> mainly because while it's technically faster, I had other higher
> priority issues to work on --- and see previous comments regarding
> pixel peeping.  Improving the hash algorithm by tens or even hundreds
> of nanoseconds isn't really going to matter since we only do a htree
> lookup on a file creation or cold cache lookup, and the SSD or HDD I/O
> times will dominate.  And from the power perspective, saving
> microwatts of CPU power isn't going to matter if you're going to be
> spinning up the storage device....

I wasn't concerned about performance but more about DoS resilience. I
wonder how safe half md4 actually is in terms of allowing users to
generate long hash chains in the filesystem (in terms of length
extension attacks against half_md4).

In ext4, is it actually possible that a "disrupter" learns about the
hashing secret in the way how the inodes are returned during getdents?

Thanks,
Hannes

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[PATCH v5 0/4] The SipHash Patchset "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-15 21:40 +0100
  [PATCH v5 4/4] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-15 21:40 +0100
  [PATCH v5 3/4] secure_seq: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-15 21:40 +0100
    RE: [PATCH v5 3/4] secure_seq: use SipHash in place of MD5 David Laight <David.Laight@ACULAB.COM> - 2016-12-16 11:10 +0100
      Re: [PATCH v5 3/4] secure_seq: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 17:00 +0100
  [PATCH v5 2/4] siphash: add Nu{32,64} helpers "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-15 21:50 +0100
    RE: [PATCH v5 2/4] siphash: add Nu{32,64} helpers David Laight <David.Laight@ACULAB.COM> - 2016-12-16 11:50 +0100
      RE: [PATCH v5 2/4] siphash: add Nu{32,64} helpers "George Spelvin" <linux@sciencehorizons.net> - 2016-12-16 16:50 +0100
  [PATCH v6 4/5] md5: remove from lib and only live in crypto "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 04:10 +0100
  [PATCH v6 2/5] secure_seq: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 04:10 +0100
  [PATCH v6 5/5] syncookies: use SipHash in place of SHA1 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 04:10 +0100
  [PATCH v6 0/5] The SipHash Patchset "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 04:10 +0100
    [PATCH v6 3/5] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 04:10 +0100
      Re: [PATCH v6 3/5] random: use SipHash in place of MD5 Andy Lutomirski <luto@amacapital.net> - 2016-12-16 22:40 +0100
    [PATCH v6 1/5] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 04:10 +0100
    [PATCH v7 0/6] The SipHash Patchset "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
      [PATCH v7 6/6] siphash: implement HalfSipHash1-3 for hash tables "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
        Re: [PATCH v7 6/6] siphash: implement HalfSipHash1-3 for hash tables Andi Kleen <ak@linux.intel.com> - 2016-12-22 01:50 +0100
      [PATCH v7 5/6] syncookies: use SipHash in place of SHA1 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
      [PATCH v7 3/6] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
        Re: [PATCH v7 3/6] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:20 +0100
        Re: [PATCH v7 3/6] random: use SipHash in place of MD5 Andy Lutomirski <luto@amacapital.net> - 2016-12-22 01:00 +0100
          Re: [PATCH v7 3/6] random: use SipHash in place of MD5 Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-22 03:10 +0100
            Re: [PATCH v7 3/6] random: use SipHash in place of MD5 Andy Lutomirski <luto@amacapital.net> - 2016-12-22 03:20 +0100
            Re: [PATCH v7 3/6] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 03:50 +0100
              Re: [PATCH v7 3/6] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 04:20 +0100
              Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Theodore Ts'o <tytso@mit.edu> - 2016-12-22 06:50 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 07:10 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Theodore Ts'o <tytso@mit.edu> - 2016-12-22 17:00 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 17:20 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Theodore Ts'o <tytso@mit.edu> - 2016-12-22 17:40 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 17:40 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-22 13:50 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 14:20 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-22 16:10 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 16:20 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 16:30 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-22 16:40 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 16:50 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-22 17:00 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 17:00 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Theodore Ts'o <tytso@mit.edu> - 2016-12-22 17:00 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-22 19:10 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 19:20 +0100
                Re: [kernel-hardening] Re: [PATCH v7 3/6] random: use SipHash in  place of MD5 Theodore Ts'o <tytso@mit.edu> - 2016-12-22 21:00 +0100
          Re: [PATCH v7 3/6] random: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 03:40 +0100
      [PATCH v7 4/6] md5: remove from lib and only live in crypto "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
      [PATCH v7 2/6] secure_seq: use SipHash in place of MD5 "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
      [PATCH v7 1/6] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-22 00:10 +0100
        Re: [PATCH v7 1/6] siphash: add cryptographically secure PRF Stephen Hemminger <stephen@networkplumber.org> - 2016-12-22 02:50 +0100

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