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@cloudflare.com>
Acked-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index f3e7ac513db3f5e4791670a071eee55b9fdf8ace..f99ab1a3b0f092d965d8eca24ce67086a34b4865 100644 (file)
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -245,7 +245,9 @@ 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) ||
+                           (file->f_mode & FMODE_WRITE)));
        if (!action && !violation_check)
                return 0;