linux-kernel - [PATCH v6 25/25] security: Enforce ordering of 'ima' and 'evm' LSMs

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Date:   Mon, 20 Nov 2023 18:33:18 +0100
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     viro@...iv.linux.org.uk, brauner@...nel.org,
        chuck.lever@...cle.com, jlayton@...nel.org, neilb@...e.de,
        kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com, mic@...ikod.net
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH v6 25/25] security: Enforce ordering of 'ima' and 'evm' LSMs

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

The ordering of LSM_ORDER_LAST LSMs depends on how they are placed in the
.lsm_info.init section of the kernel image.

Without making any assumption on the LSM ordering based on how they are
compiled, enforce that ordering at LSM infrastructure level.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 security/security.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/security/security.c b/security/security.c
index 351a124b771c..b98db79ca500 100644
--- a/security/security.c
+++ b/security/security.c
@@ -263,6 +263,18 @@ static void __init initialize_lsm(struct lsm_info *lsm)
 	}
 }
 
+/* Find an LSM with a given name. */
+static struct lsm_info __init *find_lsm(const char *name)
+{
+	struct lsm_info *lsm;
+
+	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++)
+		if (!strcmp(lsm->name, name))
+			return lsm;
+
+	return NULL;
+}
+
 /*
  * Current index to use while initializing the lsm id list.
  */
@@ -333,10 +345,23 @@ 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++) {
+		/* Do it later, to enforce the expected ordering. */
+		if (!strcmp(lsm->name, "ima") || !strcmp(lsm->name, "evm"))
+			continue;
+
 		if (lsm->order == LSM_ORDER_LAST)
 			append_ordered_lsm(lsm, "   last");
 	}
 
+	/* Ensure that the 'ima' and 'evm' LSMs are last and in this order. */
+	lsm = find_lsm("ima");
+	if (lsm)
+		append_ordered_lsm(lsm, "   last");
+
+	lsm = find_lsm("evm");
+	if (lsm)
+		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))
-- 
2.34.1