linux-kernel - Re: [PATCH v2 0/2] ima: Fix keyrings race condition and other key related bugs

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Date:   Mon, 24 Aug 2020 13:53:08 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
        Nayna Jain <nayna@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v2 0/2] ima: Fix keyrings race condition and other key
 related bugs

On 2020-08-24 14:44:55, Mimi Zohar wrote:
> Hi Tyler,
> 
> On Tue, 2020-08-11 at 14:26 -0500, Tyler Hicks wrote:
> > v2:
> >  - Always return an ERR_PTR from ima_alloc_rule_opt_list() (Nayna)
> >  - Add Lakshmi's Reviewed-by to both patches
> >  - Rebased on commit 3db0d0c276a7 ("integrity: remove redundant
> >    initialization of variable ret") of next-integrity
> > v1: https://lore.kernel.org/lkml/20200727140831.64251-1-tyhicks@linux.microsoft.com/
> > 
> > Nayna pointed out that the "keyrings=" option in an IMA policy rule
> > should only be accepted when CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is
> > enabled:
> > 
> >  https://lore.kernel.org/linux-integrity/336cc947-1f70-0286-6506-6df3d1d23a1d@linux.vnet.ibm.com/
> > 
> > While fixing this, the compiler warned me about the potential for the
> > ima_keyrings pointer to be NULL despite it being used, without a check
> > for NULL, as the destination address for the strcpy() in
> > ima_match_keyring().
> > 
> > It also became apparent that there was not adequate locking around the
> > use of the pre-allocated buffer that ima_keyrings points to. The kernel
> > keyring has a lock (.sem member of struct key) that ensures only one key
> > can be added to a given keyring at a time but there's no protection
> > against adding multiple keys to different keyrings at the same time.
> > 
> > The first patch in this series fixes both ima_keyrings related issues by
> > parsing the list of keyrings in a KEY_CHECK rule at policy load time
> > rather than deferring the parsing to policy check time. Once that fix is
> > in place, the second patch can enforce that
> > CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS must be enabled in order to use
> > "func=KEY_CHECK" or "keyrings=" options in IMA policy.
> 
> Thank you for fixing and cleaning up the existing keyring policy
> support. 
> 
> > 
> > The new "keyrings=" value handling is done in a generic manner that can
> > be reused by other options in the future. This seems to make sense as
> > "appraise_type=" has similar style (though it doesn't need to be fully
> > parsed at this time) and using "|" as an alternation delimiter is
> > becoming the norm in IMA policy.
> 
> Yes, thank you.  Better extending existing key value pairs than
> defining new boot command line options.
> 
> This patch set is now queued in next-integrity-testing.

Thanks! I'm glad you found it useful.

Tyler

> 
> Mimi