lkml.org 
[lkml]   [2020]   [Apr]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 3/5] ima: Fix ima digest hash table key calculation
    From
    Date
    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

    \
     
     \ /
      Last update: 2020-04-23 18:54    [W:4.438 / U:0.028 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site