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High severity7.8NVD Advisory· Published Feb 27, 2025· Updated May 12, 2026

CVE-2024-57979

CVE-2024-57979

Description

In the Linux kernel, the following vulnerability has been resolved:

pps: Fix a use-after-free

On a board running ntpd and gpsd, I'm seeing a consistent use-after-free in sys_exit() from gpsd when rebooting:

pps pps1: removed ------------[ cut here ]------------ kobject: '(null)' (00000000db4bec24): is not initialized, yet kobject_put() is being called. WARNING: CPU: 2 PID: 440 at lib/kobject.c:734 kobject_put+0x120/0x150 CPU: 2 UID: 299 PID: 440 Comm: gpsd Not tainted 6.11.0-rc6-00308-gb31c44928842 #1 Hardware name: Raspberry Pi 4 Model B Rev 1.1 (DT) pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : kobject_put+0x120/0x150 lr : kobject_put+0x120/0x150 sp : ffffffc0803d3ae0 x29: ffffffc0803d3ae0 x28: ffffff8042dc9738 x27: 0000000000000001 x26: 0000000000000000 x25: ffffff8042dc9040 x24: ffffff8042dc9440 x23: ffffff80402a4620 x22: ffffff8042ef4bd0 x21: ffffff80405cb600 x20: 000000000008001b x19: ffffff8040b3b6e0 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 696e6920746f6e20 x14: 7369203a29343263 x13: 205d303434542020 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000 x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000 Call trace: kobject_put+0x120/0x150 cdev_put+0x20/0x3c __fput+0x2c4/0x2d8 ____fput+0x1c/0x38 task_work_run+0x70/0xfc do_exit+0x2a0/0x924 do_group_exit+0x34/0x90 get_signal+0x7fc/0x8c0 do_signal+0x128/0x13b4 do_notify_resume+0xdc/0x160 el0_svc+0xd4/0xf8 el0t_64_sync_handler+0x140/0x14c el0t_64_sync+0x190/0x194 ---[ end trace 0000000000000000 ]---

...followed by more symptoms of corruption, with similar stacks:

refcount_t: underflow; use-after-free. kernel BUG at lib/list_debug.c:62! Kernel panic - not syncing: Oops - BUG: Fatal exception

This happens because pps_device_destruct() frees the pps_device with the embedded cdev immediately after calling cdev_del(), but, as the comment above cdev_del() notes, fops for previously opened cdevs are still callable even after cdev_del() returns. I think this bug has always been there: I can't explain why it suddenly started happening every time I reboot this particular board.

In commit d953e0e837e6 ("pps: Fix a use-after free bug when unregistering a source."), George Spelvin suggested removing the embedded cdev. That seems like the simplest way to fix this, so I've implemented his suggestion, using __register_chrdev() with pps_idr becoming the source of truth for which minor corresponds to which device.

But now that pps_idr defines userspace visibility instead of cdev_add(), we need to be sure the pps->dev refcount can't reach zero while userspace can still find it again. So, the idr_remove() call moves to pps_unregister_cdev(), and pps_idr now holds a reference to pps->dev.

pps_core: source serial1 got cdev (251:1) <...> pps pps1: removed pps_core: unregistering pps1 pps_core: deallocating pps1

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

A use-after-free in the Linux kernel's PPS subsystem allows local privilege escalation or system crash during device removal.

Vulnerability

Overview

CVE-2024-57979 is a use-after-free vulnerability in the Linux kernel's PPS (Pulse Per Second) subsystem. The flaw occurs when a PPS device is removed while a userspace process (e.g., gpsd or ntpd) still holds a file descriptor referencing the device. During removal, the kernel frees the underlying kobject without properly ensuring no remaining references exist, leading to a subsequent kobject_put() call from the process's exit path on the freed object.

Exploitation

Details

An attacker with local access and the ability to trigger PPS device removal (e.g., by disconnecting a GPS receiver or via a crafted hot-unplug event) can exploit this race condition. The attack does not require special privileges beyond the ability to open and interact with a PPS device file. The kernel's PPS subsystem is often used in time-sensitive applications such as NTP (ntpd) and GPS data processing (gpsd).

Impact

Assessment

Upon exploitation, the kernel triggers a use-after-free state, leading to system memory corruption. The observed symptoms include kernel warnings, refcount underflows, list corruption (kernel BUG at lib/list_debug.c:62), and ultimately a kernel panic. An attacker could leverage this memory corruption to escalate privileges or cause a denial of service via system crash [1].

Mitigation

Status

The fix was committed to the Linux kernel stable tree in commits [2], [3], and [4] and is expected to be backported to various distribution kernels. Users should update to a kernel version containing the patch. The vulnerability has been assigned a CVSS v3 base score of 7.8, indicating high severity. Siemens has also listed this CVE as affecting SIMATIC S7-1500 TM MFP - GNU/Linux subsystem (all versions) [1].

References
  1. SSA-265688
  2. Making sure you're not a bot!
  3. Making sure you're not a bot!
  4. Making sure you're not a bot!

AI Insight generated on May 20, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

108

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

References

11

News mentions

0

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