CVE-2026-97599 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ieee802154: hwsim: serialize pib updates to fix double-free
hwsim_update_pib() does an unserialized read-swap-free of phy->pib:
pib_old = rtnl_dereference(phy->pib); ... rcu_assign_pointer(phy->pib, pib); kfree_rcu(pib_old, rcu);
It assumes the RTNL is held, but ->set_channel is not always called under it: the mac802154 scan worker changes channels via drv_set_channel() without the RTNL. Such an update can race an RTNL-held one on the same phy; both read the same pib_old and both kfree_rcu() it, double-freeing the object. With SLUB percpu sheaves batching kfree_rcu(), this surfaces as a KASAN invalid-free in rcu_free_sheaf().
struct hwsim_phy has no lock for pib. Add one and make the swap atomic with rcu_replace_pointer() under it, dropping the misleading rtnl_dereference().
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified within the Linux kernel's ieee802154 subsystem specifically affects the hardware simulator driver known as hwsim. This issue manifests as a double-free condition arising from improper synchronization mechanisms during Physical Interface Board updates. The core of the problem lies in the function hwsim_update_pib, which manages the state of the physical layer by swapping pointers to configuration structures. Historically, this operation relied on an assumption that the RTNL lock was held throughout the execution context. This assumption proved flawed because certain code paths, particularly those involved in channel switching initiated by the mac802154 scan worker via drv_set_channel(), operate without holding the RTNL lock. Consequently, concurrent updates to the same physical interface can occur simultaneously from different contexts, leading to a race condition where multiple threads read the old pointer value and subsequently attempt to free it using kfree_rcu.
From a technical perspective, this flaw represents a classic concurrency bug involving use-after-free semantics due to lack of atomicity in pointer replacement operations. The original implementation utilized rtnl_dereference for reading the current state followed by rcu_assign_pointer for updating it, coupled with kfree_rcu for deferred freeing. While RCU provides read-side safety, it does not inherently protect against write-side races unless explicitly synchronized via locks or atomic primitives. In this scenario, two concurrent execution paths could both retrieve the same old pointer value before either had completed its update and subsequent free operation. This results in the kernel attempting to release memory that has already been freed by the other thread, triggering a double-free error. The severity of this issue is exacerbated by SLUB percpu sheaves batching mechanisms for kfree_rcu operations, which can cause such race conditions to surface as KASAN invalid-free errors within rcu_free_sheaf during runtime testing and exploitation scenarios.
The operational impact of this vulnerability includes potential kernel crashes, denial of service through system instability, and potentially arbitrary code execution if an attacker can control the memory allocation patterns following the double free. Double-free vulnerabilities are particularly dangerous because they allow attackers to manipulate heap metadata or overwrite adjacent objects with controlled data, facilitating privilege escalation or remote code execution depending on the specific context in which the vulnerable driver is utilized. Although hwsim is primarily a testing and simulation tool, its presence in production kernels expands the attack surface for local users who may have access to network interface configuration capabilities. The vulnerability aligns with CWE-415 Double Free, indicating that resources are freed more than once without proper reinitialization or nullification of pointers between operations.
To mitigate this risk, the Linux kernel maintainers implemented a fix that introduces explicit synchronization for PIB updates within the hwsim driver. This solution involves adding a dedicated lock structure to the hwsim_phy data type specifically designed to protect pib state modifications. The pointer swap operation is now performed atomically using rcu_replace_pointer under the protection of this new mutex or spinlock, ensuring that only one thread can modify the PIB at any given time. Additionally, the misleading reliance on rtnl_dereference was removed in favor of direct atomic operations synchronized by the newly added lock. This change ensures mutual exclusion during critical sections where the physical interface state is updated, thereby eliminating the race condition entirely. From a defense-in-depth perspective, this fix also aligns with ATT&CK technique T1059 Command and Scripting Interpreter if considering how such vulnerabilities might be leveraged in post-exploitation phases to maintain persistence or escalate privileges within compromised Linux environments. System administrators should ensure their kernels are updated to versions containing this patch to prevent exploitation of this concurrency flaw.