On Wed, 2023-03-08 at 09:00 -0500, Mimi Zohar wrote:

On Wed, 2023-03-08 at 14:26 +0100, Roberto Sassu wrote:

quoted

On Wed, 2023-03-08 at 08:13 -0500, Mimi Zohar wrote:

quoted

Hi Roberto,

On Fri, 2023-03-03 at 19:25 +0100, Roberto Sassu wrote:

quoted

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.

Please reframe this as a bug fix for 79f7865d844c ("LSM: Introduce
"lsm=" for boottime LSM selection") and upstream it first, with
'integrity' as the last LSM.   The original bug fix commit 92063f3ca73a
("integrity: double check iint_cache was initialized") could then be
removed.

Ok, I should complete the patch by checking the cache initialization in
iint.c.

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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.

^Similar to LSM_ORDER_FIRST ...

And remove "in no particular order".

The reason for this is that I originally thought that the relative
order of LSMs specified in the kernel configuration or the command line
was respected (if more than one LSM specifies LSM_ORDER_LAST). In fact
not. To do this, we would have to parse the LSM string again, as it is
done for LSM_ORDER_MUTABLE LSMs.

IMA and EVM are only configurable if 'integrity' is enabled.  Similar
to how LSM_ORDER_FIRST is reserved for capabilities, LSM_ORDER_LAST
should be reserved for integrity (LSMs), if it is configured, for the
reason as described in the "[PATCH 24/28] ima: Move to LSM
infrastructure" patch description.

Yes, it is just that nothing prevents to have multiple LSMs with order
LSM_ORDER_LAST. I guess we will enforce that it is only one by
reviewing the code.

Thanks

Roberto

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Thanks

Roberto

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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))