From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>
Cc: "linux-integrity@vger.kernel.org"
<linux-integrity@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Krzysztof Struczynski <krzysztof.struczynski@huawei.com>,
Silviu Vlasceanu <Silviu.Vlasceanu@huawei.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH 3/5] ima: Fix ima digest hash table key calculation
Date: Thu, 23 Apr 2020 12:53:01 -0400 [thread overview]
Message-ID: <1587660781.5610.15.camel@linux.ibm.com> (raw)
In-Reply-To: <11984a05a5624f64aed1ec6b0d0b75ff@huawei.com>
On Thu, 2020-04-23 at 10:21 +0000, Roberto Sassu wrote:
> > Hi Roberto, Krsysztof,
> >
> > On Wed, 2020-03-25 at 17:11 +0100, Roberto Sassu wrote:
> > > From: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
> > >
> > > Function hash_long() accepts unsigned long, while currently only one byte
> > > is passed from ima_hash_key(), which calculates a key for ima_htable.
> > Use
> > > more bytes to avoid frequent collisions.
> > >
> > > Length of the buffer is not explicitly passed as a function parameter,
> > > because this function expects a digest whose length is greater than the
> > > size of unsigned long.
> >
> > Somehow I missed the original report of this problem https://lore.kern
> > el.org/patchwork/patch/674684/. This patch is definitely better, but
> > how many unique keys are actually being used? Is it anywhere near
> > IMA_MEASURE_HTABLE_SIZE(512)?
>
> I did a small test (with 1043 measurements):
>
> slots: 250, max depth: 9 (without the patch)
> slots: 448, max depth: 7 (with the patch)
448 out of 512 slots are used.
>
> Then, I increased the number of bits to 10:
>
> slots: 251, max depth: 9 (without the patch)
> slots: 660, max depth: 4 (with the patch)
660 out of 1024 slots are used.
I wonder if there is any benefit to hashing a digest, instead of just
using the first bits.
>
> > Do we need a new securityfs entry to display the number used?
>
> Probably it is useful only if the administrator can decide the number of slots.
The securityfs suggestion was just a means for triggering the above
debugging info you provided. Could you provide another patch with the
debugging info?
thanks,
Mimi
next prev parent reply other threads:[~2020-04-23 16:53 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 16:11 [PATCH 1/5] ima: Set file->f_mode instead of file->f_flags in ima_calc_file_hash() Roberto Sassu
2020-03-25 16:11 ` [PATCH 2/5] evm: Check also if *tfm is an error pointer in init_desc() Roberto Sassu
2020-04-22 13:45 ` Mimi Zohar
2020-04-22 15:37 ` Roberto Sassu
2020-03-25 16:11 ` [PATCH 3/5] ima: Fix ima digest hash table key calculation Roberto Sassu
2020-04-22 20:56 ` Mimi Zohar
2020-04-23 10:21 ` Roberto Sassu
2020-04-23 16:53 ` Mimi Zohar [this message]
2020-04-24 12:18 ` Roberto Sassu
2020-04-24 14:45 ` Mimi Zohar
2020-03-25 16:14 ` [PATCH 4/5] ima: Remove redundant policy rule set in add_rules() Roberto Sassu
2020-03-25 16:14 ` [PATCH 5/5] ima: Remove unused build_ima_appraise variable Roberto Sassu
2020-04-22 22:59 ` Mimi Zohar
2020-04-22 12:03 ` [PATCH 1/5] ima: Set file->f_mode instead of file->f_flags in ima_calc_file_hash() Mimi Zohar
2020-04-22 15:39 ` Roberto Sassu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1587660781.5610.15.camel@linux.ibm.com \
--to=zohar@linux.ibm.com \
--cc=Silviu.Vlasceanu@huawei.com \
--cc=krzysztof.struczynski@huawei.com \
--cc=linux-integrity@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=roberto.sassu@huawei.com \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).