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From: Roberto Sassu <roberto.sassu@huawei.com>
To: <zohar@linux.ibm.com>, <mjg59@google.com>
Cc: <linux-integrity@vger.kernel.org>,
	<linux-security-module@vger.kernel.org>,
	<linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<silviu.vlasceanu@huawei.com>,
	Roberto Sassu <roberto.sassu@huawei.com>,
	<stable@vger.kernel.org>
Subject: [PATCH v3 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded
Date: Wed, 11 Nov 2020 10:22:54 +0100	[thread overview]
Message-ID: <20201111092302.1589-4-roberto.sassu@huawei.com> (raw)
In-Reply-To: <20201111092302.1589-1-roberto.sassu@huawei.com>

EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be set to
temporarily disable metadata verification until all xattrs/attrs necessary
to verify an EVM portable signature are copied to the file. This flag is
cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is
calculated on unverified xattrs/attrs.

Currently EVM unnecessarily denies setting this flag if EVM is initialized
with a public key, which is not a concern as it cannot be used to trust
xattrs/attrs updates. This patch removes this limitation.

Cc: stable@vger.kernel.org # 4.16.x
Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 Documentation/ABI/testing/evm      | 5 +++--
 security/integrity/evm/evm_secfs.c | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm
index 3c477ba48a31..eb6d70fd6fa2 100644
--- a/Documentation/ABI/testing/evm
+++ b/Documentation/ABI/testing/evm
@@ -49,8 +49,9 @@ Description:
 		modification of EVM-protected metadata and
 		disable all further modification of policy
 
-		Note that once a key has been loaded, it will no longer be
-		possible to enable metadata modification.
+		Note that once an HMAC key has been loaded, it will no longer
+		be possible to enable metadata modification and, if it is
+		already enabled, it will be disabled.
 
 		Until key loading has been signaled EVM can not create
 		or validate the 'security.evm' xattr, but returns
diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index cfc3075769bb..92fe26ace797 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c
@@ -84,7 +84,7 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
 	 * keys are loaded.
 	 */
 	if ((i & EVM_ALLOW_METADATA_WRITES) &&
-	    ((evm_initialized & EVM_KEY_MASK) != 0) &&
+	    ((evm_initialized & EVM_INIT_HMAC) != 0) &&
 	    !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
 		return -EPERM;
 
-- 
2.27.GIT


  parent reply	other threads:[~2020-11-11  9:24 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-11  9:22 [PATCH v3 00/11] evm: Improve usability of portable signatures Roberto Sassu
2020-11-11  9:22 ` [PATCH v3 01/11] evm: Execute evm_inode_init_security() only when an HMAC key is loaded Roberto Sassu
2020-12-02 17:03   ` Mimi Zohar
2020-11-11  9:22 ` [PATCH v3 02/11] evm: Load EVM key in ima_load_x509() to avoid appraisal Roberto Sassu
2020-12-02 17:27   ` Mimi Zohar
2021-03-01 18:06   ` Mimi Zohar
2020-11-11  9:22 ` Roberto Sassu [this message]
2020-12-02 21:07   ` [PATCH v3 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Mimi Zohar
2020-11-11  9:22 ` [PATCH v3 04/11] ima: Move ima_reset_appraise_flags() call to post hooks Roberto Sassu
2020-12-02 11:56   ` Roberto Sassu
2020-12-03 20:43     ` Mimi Zohar
2020-11-11  9:22 ` [PATCH v3 05/11] evm: Introduce evm_status_revalidate() Roberto Sassu
2020-11-11  9:22 ` [PATCH v3 06/11] evm: Ignore INTEGRITY_NOLABEL if no HMAC key is loaded Roberto Sassu
2020-12-03 20:42   ` Mimi Zohar
2020-12-04  8:05     ` Roberto Sassu
2020-12-04 13:04       ` Mimi Zohar
2020-12-04 14:59         ` Roberto Sassu
2020-11-11  9:22 ` [PATCH v3 07/11] evm: Allow xattr/attr operations for portable signatures Roberto Sassu
2020-11-11  9:22 ` [PATCH v3 08/11] evm: Allow setxattr() and setattr() for unmodified metadata Roberto Sassu
2020-11-18 17:58   ` kernel test robot
2020-11-18 17:58     ` kernel test robot
2020-11-11  9:23 ` [PATCH v3 09/11] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2020-11-11  9:23 ` [PATCH v3 10/11] ima: Introduce template field evmsig and write to field sig as fallback Roberto Sassu
2020-11-11  9:23 ` [PATCH v3 11/11] ima: Don't remove security.ima if file must not be appraised Roberto Sassu
2020-12-01 20:52 ` [PATCH v3 00/11] evm: Improve usability of portable signatures Mimi Zohar

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