linux-kernel - [PATCH] smackfs: Use rcu_assign_pointer() to ensure safe assignment in smk_set

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Message-ID: <tencent_39FA49154F494DFE0FEC2F20A9A34AA9B308@qq.com>
Date: Mon,  2 Sep 2024 08:47:26 +0000
From: Jiawei Ye <jiawei.ye@...mail.com>
To: casey@...aufler-ca.com,
	paul@...l-moore.com,
	jmorris@...ei.org,
	serge@...lyn.com,
	pawan.kumar.gupta@...ux.intel.com
Cc: linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] smackfs: Use rcu_assign_pointer() to ensure safe assignment in smk_set_cipso

In the `smk_set_cipso` function, the `skp->smk_netlabel.attr.mls.cat`
field is directly assigned to a new value without using the appropriate
RCU pointer assignment functions. According to RCU usage rules, this is
illegal and can lead to unpredictable behavior, including data
inconsistencies and impossible-to-diagnose memory corruption issues.

This possible bug was identified using a static analysis tool developed
by myself, specifically designed to detect RCU-related issues.

To address this, the assignment is now done using rcu_assign_pointer(),
which ensures that the pointer assignment is done safely, with the
necessary memory barriers and synchronization. This change prevents
potential RCU dereference issues by ensuring that the `cat` field is
safely updated while still adhering to RCU's requirements.

Fixes: 0817534ff9ea ("smackfs: Fix use-after-free in netlbl_catmap_walk()")
Signed-off-by: Jiawei Ye <jiawei.ye@...mail.com>
---
 security/smack/smackfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index e22aad7604e8..5dd1e164f9b1 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -932,7 +932,7 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf,
 	}
 	if (rc >= 0) {
 		old_cat = skp->smk_netlabel.attr.mls.cat;
-		skp->smk_netlabel.attr.mls.cat = ncats.attr.mls.cat;
+		rcu_assign_pointer(skp->smk_netlabel.attr.mls.cat, ncats.attr.mls.cat);
 		skp->smk_netlabel.attr.mls.lvl = ncats.attr.mls.lvl;
 		synchronize_rcu();
 		netlbl_catmap_free(old_cat);
-- 
2.34.1