linux-kernel - [PATCH v3 5/5] LSM: secctx provider check on release

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Message-ID: <20241023212158.18718-6-casey@schaufler-ca.com>
Date: Wed, 23 Oct 2024 14:21:58 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: casey@...aufler-ca.com,
	paul@...l-moore.com,
	linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org,
	serge@...lyn.com,
	keescook@...omium.org,
	john.johansen@...onical.com,
	penguin-kernel@...ove.sakura.ne.jp,
	stephen.smalley.work@...il.com,
	linux-kernel@...r.kernel.org,
	selinux@...r.kernel.org,
	mic@...ikod.net
Subject: [PATCH v3 5/5] LSM: secctx provider check on release

Verify that the LSM releasing the secctx is the LSM that
allocated it. This was not necessary when only one LSM could
create a secctx, but once there can be more than one it is.

Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
---
 security/apparmor/secid.c | 13 +++++--------
 security/selinux/hooks.c  | 13 +++++--------
 2 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/security/apparmor/secid.c b/security/apparmor/secid.c
index 5d92fc3ab8b4..854613e58e34 100644
--- a/security/apparmor/secid.c
+++ b/security/apparmor/secid.c
@@ -122,14 +122,11 @@ int apparmor_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
 
 void apparmor_release_secctx(struct lsm_context *cp)
 {
-	/*
-	 * stacking scaffolding:
-	 * When it is possible for more than one LSM to provide a
-	 * release hook, do this check:
-	 * if (cp->id == LSM_ID_APPARMOR || cp->id == LSM_ID_UNDEF)
-	 */
-
-	kfree(cp->context);
+	if (cp->id == LSM_ID_APPARMOR) {
+		kfree(cp->context);
+		cp->context = NULL;
+		cp->id = LSM_ID_UNDEF;
+	}
 }
 
 /**
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 79776a5e651d..996e765b6823 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6640,14 +6640,11 @@ static int selinux_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
 
 static void selinux_release_secctx(struct lsm_context *cp)
 {
-	/*
-	 * stacking scaffolding:
-	 * When it is possible for more than one LSM to provide a
-	 * release hook, do this check:
-	 * if (cp->id == LSM_ID_SELINUX || cp->id == LSM_ID_UNDEF)
-	 */
-
-	kfree(cp->context);
+	if (cp->id == LSM_ID_SELINUX) {
+		kfree(cp->context);
+		cp->context = NULL;
+		cp->id = LSM_ID_UNDEF;
+	}
 }
 
 static void selinux_inode_invalidate_secctx(struct inode *inode)
-- 
2.46.0