CVE-2026-52946
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk38th percentile - higher than 38% of all known CVEs
Summary
A SOFTIRQ-unsafe lock order deadlock was found in the Linux kernel's send_sigio() and send_sigurg() functions when signaling a process group (PIDTYPE_PGID). The use of read_lock(&tasklist_lock) combined with write_lock in fork()/exit() and softirq interrupts (e.g., TCP URG) causes a deadlock. The fix replaces tasklist_lock with rcu_read_lock().
Risk Assessment
An attacker can remotely trigger a kernel deadlock by sending TCP URG packets, causing a denial of service (DoS) for the entire system. The vulnerability affects systems with FASYNC enabled for process groups.
Recommendation
Apply the Linux kernel patch that replaces read_lock(&tasklist_lock) with rcu_read_lock() in send_sigio() and send_sigurg(). Update the kernel to a version containing this fix.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling A SOFTIRQ-safe to SOFTIRQ-unsafe lock order deadlock can occur in send_sigio() and send_sigurg() when a process group receives a signal. When FASYNC is configured for a process group (PIDTYPE_PGID), both functions use read_lock(&tasklist_lock) to traverse the task list. However, they are frequently called from softirq context: - send_sigio() via input_inject_event -> kill_fasync - send_sigurg() via tcp_check_urg -> sk_send_sigurg (NET_RX_SOFTIRQ) The deadlock is caused by the rwlock writer fairness mechanism: 1. CPU 0 (process context) holds read_lock(&tasklist_lock) in do_wait(). 2. CPU 1 (process context) attempts write_lock(&tasklist_lock) in fork() or exit() and spins, which blocks all new readers. 3. CPU 0 is interrupted by a softirq (e.g., TCP URG packet reception). 4. The softirq calls send_sigurg() and attempts to acquire read_lock(&tasklist_lock), deadlocking because CPU 1 is waiting. Since PID hashing and do_each_pid_task() traversals are already RCU-protected, the read_lock on tasklist_lock is no longer strictly required for safe traversal. Fix this by replacing tasklist_lock with rcu_read_lock(), aligning the process group signaling path with the single-PID path. This also mitigates a potential remote denial of service vector via TCP URG packets. Lockdep splat: ===================================================== WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected [...] Chain exists of: &dev->event_lock --> &f_owner->lock --> tasklist_lock Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(tasklist_lock); local_irq_disable(); lock(&dev->event_lock); lock(&f_owner->lock); <Interrupt> lock(&dev->event_lock); *** DEADLOCK ***