CVE-2026-63980 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net/handshake: Use spin_lock_bh for hn_lock
nvmet_tcp_state_change(), a socket callback that runs in BH context, can reach handshake_req_cancel() via nvmet_tcp_schedule_release_queue() and tls_handshake_cancel(). handshake_req_cancel() acquires hn->hn_lock with plain spin_lock(). If a process-context thread on the same CPU holds hn->hn_lock when a softirq invokes the cancel path, the lock attempt deadlocks. This is the only caller that invokes tls_handshake_cancel() from BH context; every other consumer calls it from process context.
Deferring the cancel to process context in the NVMe target is not straightforward: nvmet_tcp_schedule_release_queue() must call tls_handshake_cancel() atomically with its state transition to DISCONNECTING. If the cancel were deferred, the handshake completion callback could fire in the window before the cancel runs, observe the unexpected state, and return without dropping its kref on the queue. Reworking that interlock is considerably more invasive than hardening the handshake lock. Convert all hn->hn_lock acquisitions from spin_lock/spin_unlock to spin_lock_bh/spin_unlock_bh so the lock is never taken with softirqs enabled.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists within the Linux kernel's networking stack, specifically affecting the NVMe over TCP target implementation where a potential deadlock condition can occur due to improper locking mechanisms during handshake operations. The issue manifests in the net/handshake subsystem where the hn_lock spinlock is acquired using standard spin_lock() instead of the more appropriate spin_lock_bh() function. The vulnerability stems from the fact that nvmet_tcp_state_change() operates within bottom-half (BH) context, which can invoke handshake_req_cancel() through nvmet_tcp_schedule_release_queue() and tls_handshake_cancel() functions, creating a scenario where process-context threads holding the lock can cause deadlocks when softirqs attempt to acquire it.
The technical flaw represents a classic concurrency issue where locking primitives are not properly adapted to their execution context. When a softirq executes in BH context and attempts to acquire a spinlock that is already held by a process-context thread running on the same CPU, the system enters a deadlock state. This occurs because standard spin_lock() does not disable softirqs, allowing the interrupt context to potentially block indefinitely while waiting for a lock held by another thread that may never release it due to the scheduling constraints of the softirq execution environment. The vulnerability is particularly insidious because it only affects systems where both contexts operate on the same CPU core, making detection challenging in typical deployment scenarios.
The operational impact of this vulnerability extends beyond simple system stability issues to potentially compromise data integrity and availability in NVMe over TCP target environments. Systems utilizing NVMe target functionality with TCP transport could experience complete service disruption when handshake operations trigger the deadlock condition, leading to unresponsive targets and potential data loss during critical I/O operations. The vulnerability affects enterprise storage systems where NVMe over Fabrics implementations are deployed, particularly in high-performance computing environments where reliable storage connectivity is paramount. Attackers could potentially exploit this weakness to cause denial of service conditions that would require system reboot to resolve, disrupting business-critical storage operations.
The mitigation strategy involves converting all hn->hn_lock acquisitions from standard spin_lock/spin_unlock to spin_lock_bh/spin_unlock_bh functions, ensuring that locks are never taken with softirqs enabled. This approach directly addresses the root cause by making the locking mechanism context-aware and preventing the deadlock scenario entirely. The solution aligns with security best practices outlined in CWE-362, which addresses race conditions and concurrent access issues in multi-threaded environments. This fix also corresponds to ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, as the vulnerability could be exploited to cause system unresponsiveness through lock contention. The implementation maintains the existing locking semantics while ensuring proper context handling, making it a minimal but effective patch that preserves system functionality while eliminating the deadlock condition. This approach is preferred over more invasive rework of the interlock mechanisms because it directly targets the specific problematic behavior without altering the complex state transition logic that governs the NVMe TCP target operations.