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

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Date:   Tue, 11 Aug 2020 14:26:19 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:     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: [PATCH v2 0/2] ima: Fix keyrings race condition and other key related bugs

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.

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.

This series is based on commit 311aa6aafea4 ("ima: move
APPRAISE_BOOTPARAM dependency on ARCH_POLICY to runtime") in
next-integrity.

Tyler

Tyler Hicks (2):
  ima: Pre-parse the list of keyrings in a KEY_CHECK rule
  ima: Fail rule parsing when asymmetric key measurement isn't
    supportable

 security/integrity/ima/ima_policy.c | 142 +++++++++++++++++++---------
 1 file changed, 96 insertions(+), 46 deletions(-)

-- 
2.25.1