[PATCH] ima: process_measurement() needlessly takes inode_lock() on MAY_READ

[Frederick Lawler]

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 at cloudflare.com>
---
 security/integrity/ima/ima_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 2aebb7984437..78921e69ee14 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -181,7 +181,7 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
 	action = ima_get_action(inode, mask, func, &pcr);
 	violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
 			   (ima_policy_flag & IMA_MEASURE));
-	if (!action && !violation_check)
+	if (!action && (mask == MAY_READ || !violation_check))
 		return 0;
 
 	must_appraise = action & IMA_APPRAISE;
-- 
2.43.0