Re: [PATCH] smackfs: Use rcu_assign_pointer() to ensure safe assignment in smk_set_cipso
From: Casey Schaufler <casey@schaufler-ca.com>
Date: 2024-09-03 15:38:36
Also in:
lkml
On 9/2/2024 1:47 AM, Jiawei Ye wrote:
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 <redacted>Applied to the smack-next tree. Thank you.
quoted hunk ↗ jump to hunk
--- 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);