linux-kernel - [PATCH v2 2/4] evm: skip replacing EVM signature with HMAC on read-only filesystem

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Date:	Wed,  1 Oct 2014 21:43:08 +0300
From:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
To:	zohar@...ux.vnet.ibm.com, linux-ima-devel@...ts.sourceforge.net,
	linux-security-module@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Dmitry Kasatkin <d.kasatkin@...sung.com>
Subject: [PATCH v2 2/4] evm: skip replacing EVM signature with HMAC on read-only filesystem

If filesystem is mounted read-only or file is immutable, updating
xattr will fail. This is a usual case during early boot until
filesystem is remount read-write. This patch verifies conditions
to skip unnecessary attempt to calculate HMAC and set xattr.

Changes in v2:
* indention changed according to Lindent (requested by Mimi)

Signed-off-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
---
 security/integrity/evm/evm_main.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 9685af3..b392fe6 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -162,9 +162,14 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 					(const char *)xattr_data, xattr_len,
 					calc.digest, sizeof(calc.digest));
 		if (!rc) {
-			/* we probably want to replace rsa with hmac here */
-			evm_update_evmxattr(dentry, xattr_name, xattr_value,
-				   xattr_value_len);
+			/* Replace RSA with HMAC if not mounted readonly and
+			 * not immutable
+			 */
+			if (!IS_RDONLY(dentry->d_inode) &&
+			    !IS_IMMUTABLE(dentry->d_inode))
+				evm_update_evmxattr(dentry, xattr_name,
+						    xattr_value,
+						    xattr_value_len);
 		}
 		break;
 	default:
-- 
1.9.1

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