[0/2] ima: Fix keyrings race condition and other key related bugs

Message

Tyler Hicks July 27, 2020, 2:08 p.m. UTC

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/[e-mail]/

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(-)