CVE-2023-53623

Medium · 4.7

CVSS

4.7

EPSS

0.1%

Published

Oct 7, 2025

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

A flaw in how the operating system manages swap space can let a local user crash the entire system under specific heavy memory conditions.

Exploitation: Local Privilege
Attacker needs: Low Privilege
Complexity: High
Impact: Denial Of Service
Component: OS kernel
Class: Race Condition
Remediation: Patch
Effort: Medium
Patch risk: Low

What it actually does

Race condition in swap_info_struct handling allows concurrent swapoff and get_swap_pages operations to corrupt internal swap availability lists when si->lock is not held during deletion from the available list.

Why it matters to the business

Systems performing frequent swap on/off operations under memory pressure can experience kernel panics, warnings, or memory corruption leading to instability and potential data loss in production workloads.

How an attack unfolds

An attacker with local access triggers concurrent madvise(MADV_PAGEOUT) calls while rapidly executing swapon/swapoff sequences; the race allows re-insertion of a deleted swap_info_struct, resulting in list corruption that manifests as plist warnings or kernel panic on subsequent allocation attempts.

How to fix it

Apply the upstream fix that acquires si->lock before calling del_from_avail_list in the swapoff path; update to a kernel version containing the resolution for CVE-2023-53623 after 5.10.y stable releases.

How to confirm the fix worked

Confirm the lock acquisition precedes del_from_avail_list in swapoff source; test with stress-ng-swap and concurrent madvise under CONFIG_PLIST_DEBUG to verify absence of plist_check warnings or panics.

Typical attack path

Obtain local unprivileged access to a Linux system using swap.
Run stress-ng-swap or equivalent to perform rapid swapon/swapoff cycles.
Concurrently invoke madvise(MADV_PAGEOUT) on large memory regions.
Trigger the window where del_from_avail_list races with re-add under swap_avail_lock.
Cause list corruption leading to panic or continued memory corruption on next swapon.

How to detect it

Review kernel logs for plist_check_prev_next_node warnings or panic traces involving swapoff and add_to_avail_list; correlate with processes performing frequent swapon/swapoff or madvise calls.

plist_check_prev_next_node+0x50/0x70
WARNING: CPU.*PID.*at lib/plist.c:60
stress-ng.*swap
madvise.*MADV_PAGEOUT

What your security team should do

Prioritize patching kernel packages on systems with heavy swap usage or container workloads.
Monitor for kernel warnings referencing plist_check_prev_next_node during swap operations.
Limit unprivileged swapoff/swapon capabilities via SELinux or AppArmor where feasible.
Schedule kernel updates before the next maintenance window on affected distributions.

The record

In the Linux kernel, the following vulnerability has been resolved: mm/swap: fix swap_info_struct race between swapoff and get_swap_pages() The si->lock must be held when deleting the si from the available list. Otherwise, another thread can re-add the si to the available list, which can lead to memory corruption. The only place we have found where this happens is in the swapoff path. This case can be described as below: core 0 core 1 swapoff del_from_avail_list(si) waiting try lock si->lock acquire swap_avail_lock and re-add si into swap_avail_head acquire si->lock but missing si already being added again, and continuing to clear SWP_WRITEOK, etc. It can be easily found that a massive warning messages can be triggered inside get_swap_pages() by some special cases, for example, we call madvise(MADV_PAGEOUT) on blocks of touched memory concurrently, meanwhile, run much swapon-swapoff operations (e.g. stress-ng-swap). However, in the worst case, panic can be caused by the above scene. In swapoff(), the memory used by si could be kept in swap_info[] after turning off a swap. This means memory corruption will not be caused immediately until allocated and reset for a new swap in the swapon path. A panic message caused: (with CONFIG_PLIST_DEBUG enabled) ------------[ cut here ]------------ top: 00000000e58a3003, n: 0000000013e75cda, p: 000000008cd4451a prev: 0000000035b1e58a, n: 000000008cd4451a, p: 000000002150ee8d next: 000000008cd4451a, n: 000000008cd4451a, p: 000000008cd4451a WARNING: CPU: 21 PID: 1843 at lib/plist.c:60 plist_check_prev_next_node+0x50/0x70 Modules linked in: rfkill(E) crct10dif_ce(E)... CPU: 21 PID: 1843 Comm: stress-ng Kdump: ... 5.10.134+ Hardware name: Alibaba Cloud ECS, BIOS 0.0.0 02/06/2015 pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) pc : plist_check_prev_next_node+0x50/0x70 lr : plist_check_prev_next_node+0x50/0x70 sp : ffff0018009d3c30 x29: ffff0018009d3c40 x28: ffff800011b32a98 x27: 0000000000000000 x26: ffff001803908000 x25: ffff8000128ea088 x24: ffff800011b32a48 x23: 0000000000000028 x22: ffff001800875c00 x21: ffff800010f9e520 x20: ffff001800875c00 x19: ffff001800fdc6e0 x18: 0000000000000030 x17: 0000000000000000 x16: 0000000000000000 x15: 0736076307640766 x14: 0730073007380731 x13: 0736076307640766 x12: 0730073007380731 x11: 000000000004058d x10: 0000000085a85b76 x9 : ffff8000101436e4 x8 : ffff800011c8ce08 x7 : 0000000000000000 x6 : 0000000000000001 x5 : ffff0017df9ed338 x4 : 0000000000000001 x3 : ffff8017ce62a000 x2 : ffff0017df9ed340 x1 : 0000000000000000 x0 : 0000000000000000 Call trace: plist_check_prev_next_node+0x50/0x70 plist_check_head+0x80/0xf0 plist_add+0x28/0x140 add_to_avail_list+0x9c/0xf0 _enable_swap_info+0x78/0xb4 __do_sys_swapon+0x918/0xa10 __arm64_sys_swapon+0x20/0x30 el0_svc_common+0x8c/0x220 do_el0_svc+0x2c/0x90 el0_svc+0x1c/0x30 el0_sync_handler+0xa8/0xb0 el0_sync+0x148/0x180 irq event stamp: 2082270 Now, si->lock locked before calling 'del_from_avail_list()' to make sure other thread see the si had been deleted and SWP_WRITEOK cleared together, will not reinsert again. This problem exists in versions after stable 5.10.y.

Affected packages

Ecosystem	Package	Introduced	Fixed
Linux	Kernel	4.14.0	4.14.313