CVE-2026-52946

/// Technical description

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_

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References