linux-kernel - [PATCH] ima: process_measurement() needlessly takes inode_lock() on MAY

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Message-ID: <20250325181616.79540-2-fred@cloudflare.com>
Date: Tue, 25 Mar 2025 13:15:03 -0500
From: Frederick Lawler <fred@...udflare.com>
To: Mimi Zohar <zohar@...ux.ibm.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
	Roberto Sassu <roberto.sassu@...wei.com>
Cc: Eric Snowberg <eric.snowberg@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	linux-ima-devel@...ts.sourceforge.net,
	linux-integrity@...r.kernel.org,
	linux-ima-user@...ts.sourceforge.net,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...udfalre.com,
	Frederick Lawler <fred@...udflare.com>
Subject: [PATCH] ima: process_measurement() needlessly takes inode_lock() on MAY_READ

On IMA policy update, if a measure rule exists in the policy,
IMA_MEASURE is set for ima_policy_flags which makes the violation_check
variable always true. Coupled with a no-action on MAY_READ for a
FILE_CHECK call, we're always taking the inode_lock().

This becomes a performance problem for extremely heavy read-only workloads.
Therefore, prevent this only in the case there's no action to be taken.

Signed-off-by: Frederick Lawler <fred@...udflare.com>
---
Changes since v1:
- Add MAY_WRITE && action check to violation_check to avoid MAY_READ
  only situations
---
 security/integrity/ima/ima_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 9b87556b03a7..11a91d9dae48 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -237,7 +237,8 @@ static int process_measurement(struct file *file, const struct cred *cred,
 				&allowed_algos);
 	violation_check = ((func == FILE_CHECK || func == MMAP_CHECK ||
 			    func == MMAP_CHECK_REQPROT) &&
-			   (ima_policy_flag & IMA_MEASURE));
+			   (ima_policy_flag & IMA_MEASURE) &&
+			   ((action & IMA_MEASURE) || (mask & MAY_WRITE)));
 	if (!action && !violation_check)
 		return 0;
 
-- 
2.43.0