Commit 8ecd39cb authored Aug 16, 2021 by THOBY Simon Committed by Mimi Zohar Aug 16, 2021

IMA: prevent SETXATTR_CHECK policy rules with unavailable algorithms



SETXATTR_CHECK policy rules assume that any algorithm listed in the
'appraise_algos' flag must be accepted when performing setxattr() on
the security.ima xattr.  However nothing checks that they are
available in the current kernel.  A userland application could hash
a file with a digest that the kernel wouldn't be able to verify.
However, if SETXATTR_CHECK is not in use, the kernel already forbids
that xattr write.

Verify that algorithms listed in appraise_algos are available to the
current kernel and reject the policy update otherwise. This will fix
the inconsistency between SETXATTR_CHECK and non-SETXATTR_CHECK
behaviors.

That filtering is only performed in ima_parse_appraise_algos() when
updating policies so that we do not have to pay the price of
allocating a hash object every time validate_hash_algo() is called
in ima_inode_setxattr().

Signed-off-by: THOBY Simon <Simon.THOBY@viveris.fr>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

parent 4f2946aa

security/integrity/ima/ima_policy.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -1258,6 +1258,12 @@ static unsigned int ima_parse_appraise_algos(char *arg)
		return 0;
		}

		if (!crypto_has_alg(hash_algo_name[idx], 0, 0)) {
		pr_err("unavailable hash algorithm \"%s\", check your kernel configuration",
		token);
		return 0;
		}

		/* Add the hash algorithm to the 'allowed' bitfield */
		res \|= (1U << idx);
		}