# CVE-2026-52946: fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling

Status: published. Published: 2026-06-24. Updated: 2026-11-10.

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 ***

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 54626335ea4174ab2d9a183b511d825f6765e47b (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 897d6a7247739fb1528f98c575df4f2e5de7f994 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < b5fa9e32fb6718f70c986ee14dd5d01b4846f331 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 1bee417678f1135e35b25a37734db46aa94258d2 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 20a93e397abe850c49b6fa0e8cc827b5f634a8f5 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < bfcc8e8d8a495bb34cae9e620adfb75fb13a3954 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 00633c4683828acd5256fa8d5163f440d74bbe71 (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.12 (affected); ≥ 0; < 2.6.12 (unaffected, semver); ≥ 5.10.259; ≤ 5.10.* (unaffected, semver); ≥ 5.15.210; ≤ 5.15.* (unaffected, semver); ≥ 6.1.176; ≤ 6.1.* (unaffected, semver); ≥ 6.6.143; ≤ 6.6.* (unaffected, semver); ≥ 6.12.94; ≤ 6.12.* (unaffected, semver); ≥ 6.18.36; ≤ 6.18.* (unaffected, semver); ≥ 7.0.13; ≤ 7.0.* (unaffected, semver); ≥ 7.1.1; ≤ 7.1.* (unaffected, semver); ≥ 7.2; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 TM MFP - GNU/Linux subsystem: ≥ 0; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: Linux

- CISA KEV: No listing in collected sources

- EPSS: 0.47% as of 2026-11-09; percentile 40.72%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-362

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b (CNA: Linux)

- https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994 (CNA: Linux)

- https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33 (CNA: Linux)

- https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331 (CNA: Linux)

- https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2 (CNA: Linux)

- https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5 (CNA: Linux)

- https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954 (CNA: Linux)

- https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed (CNA: Linux)

- https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71 (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-784472.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-52946; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-52946; retrieved 2026-11-10; source updated Not reported

Revision: 7b892a94b78bf706c4503e206e3e82e9c0e442af8fd0dbe08e8aa6634af88e5f

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