[PATCH 23/28] security: Introduce LSM_ORDER_LAST

[Roberto Sassu <roberto.sassu@huaweicloud.com>]

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce LSM_ORDER_LAST, to satisfy the requirement of LSMs willing to be
the last, e.g. the 'integrity' LSM, without changing the kernel command
line or configuration.

As for LSM_ORDER_FIRST, LSMs with LSM_ORDER_LAST are always enabled and put
at the end of the LSM list in no particular order.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/lsm_hooks.h |  1 +
 security/security.c       | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 21a8ce23108..05c4b831d99 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -93,6 +93,7 @@ extern void security_add_hooks(struct security_hook_list *hooks, int count,
 enum lsm_order {
 	LSM_ORDER_FIRST = -1,	/* This is only for capabilities. */
 	LSM_ORDER_MUTABLE = 0,
+	LSM_ORDER_LAST = 1,
 };
 
 struct lsm_info {
diff --git a/security/security.c b/security/security.c
index 322090a50cd..24f52ba3218 100644
--- a/security/security.c
+++ b/security/security.c
@@ -284,9 +284,9 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
 		bool found = false;
 
 		for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
-			if (lsm->order == LSM_ORDER_MUTABLE &&
-			    strcmp(lsm->name, name) == 0) {
-				append_ordered_lsm(lsm, origin);
+			if (strcmp(lsm->name, name) == 0) {
+				if (lsm->order == LSM_ORDER_MUTABLE)
+					append_ordered_lsm(lsm, origin);
 				found = true;
 			}
 		}
@@ -306,6 +306,12 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
 		}
 	}
 
+	/* LSM_ORDER_LAST is always last. */
+	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
+		if (lsm->order == LSM_ORDER_LAST)
+			append_ordered_lsm(lsm, "   last");
+	}
+
 	/* Disable all LSMs not in the ordered list. */
 	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
 		if (exists_ordered_lsm(lsm))
-- 
2.25.1