ima: prevent unnecessary policy checking

ima_rdwr_violation_check is called for every file openning.
The function checks the policy even when violation condition
is not met. It causes unnecessary policy checking.

This patch does policy checking only if violation condition is met.

Changelog:
- check writecount is greater than zero (Mimi)
Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_main.c

@@ -81,7 +81,6 @@ static void ima_rdwr_violation_check(struct file *file)
 {
 	struct inode *inode = file_inode(file);
 	fmode_t mode = file->f_mode;
-	int must_measure;
 	bool send_tomtou = false, send_writers = false;
 	char *pathbuf = NULL;
 	const char *pathname;
@@ -94,16 +93,12 @@ static void ima_rdwr_violation_check(struct file *file)
 	if (mode & FMODE_WRITE) {
 		if (atomic_read(&inode->i_readcount) && IS_IMA(inode))
 			send_tomtou = true;
-		goto out;
+	} else {
+		if ((atomic_read(&inode->i_writecount) > 0) &&
+		    ima_must_measure(inode, MAY_READ, FILE_CHECK))
+			send_writers = true;
 	}
 
-	must_measure = ima_must_measure(inode, MAY_READ, FILE_CHECK);
-	if (!must_measure)
-		goto out;
-
-	if (atomic_read(&inode->i_writecount) > 0)
-		send_writers = true;
-out:
 	mutex_unlock(&inode->i_mutex);
 
 	if (!send_tomtou && !send_writers)