ima: Fix a potential integer overflow in ima_appraise_measurement

When the ima-modsig is enabled, the rc passed to evm_verifyxattr() may be
negative, which may cause the integer overflow problem.

Fixes: 39b07096 ("ima: Implement support for module-style appended signatures")
Signed-off-by: Huaxin Lu <luhuaxin1@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima_appraise.c

@@ -514,7 +514,8 @@ int ima_appraise_measurement(enum ima_hooks func,
 		goto out;
 	}
 
-	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
+	status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value,
+				 rc < 0 ? 0 : rc, iint);
 	switch (status) {
 	case INTEGRITY_PASS:
 	case INTEGRITY_PASS_IMMUTABLE: