linux-kernel - [PATCH 01/11] evm: Execute evm_inode_init_security() only when the HMAC key is loaded

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Message-ID: <20200618160133.937-1-roberto.sassu@huawei.com>
Date:   Thu, 18 Jun 2020 18:01:23 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     <zohar@...ux.ibm.com>, <mjg59@...gle.com>
CC:     <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        <stable@...r.kernel.org>
Subject: [PATCH 01/11] evm: Execute evm_inode_init_security() only when the HMAC key is loaded

evm_inode_init_security() requires the HMAC key to calculate the HMAC on
initial xattrs provided by LSMs. Unfortunately, with the evm_key_loaded()
check, the function continues even if the HMAC key is not loaded
(evm_key_loaded() returns true also if EVM has been initialized only with a
public key). If the HMAC key is not loaded, evm_inode_init_security()
returns an error later when it calls evm_init_hmac().

Thus, this patch replaces the evm_key_loaded() check with a check of the
EVM_INIT_HMAC flag in evm_initialized, so that evm_inode_init_security()
returns 0 instead of an error.

Cc: stable@...r.kernel.org # 4.5.x
Fixes: 26ddabfe96b ("evm: enable EVM when X509 certificate is loaded")
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 security/integrity/evm/evm_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 0d36259b690d..744c105b48d1 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -521,7 +521,8 @@ int evm_inode_init_security(struct inode *inode,
 	struct evm_xattr *xattr_data;
 	int rc;

-	if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
+	if (!(evm_initialized & EVM_INIT_HMAC) ||
+	    !evm_protected_xattr(lsm_xattr->name))
 		return 0;

 	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
-- 
2.17.1