CVE-2025-38517

What it is

In the Linux kernel, the following vulnerability has been resolved: lib/alloc_tag: do not acquire non-existent lock in alloc_tag_top_users() alloc_tag_top_users() attempts to lock alloc_tag_cttype->mod_lock even when the alloc_tag_cttype is not allocated because: 1) alloc tagging is disabled because mem profiling is disabled (!alloc_tag_cttype) 2) alloc tagging is enabled, but not yet initialized (!alloc_tag_cttype) 3) alloc tagging is enabled, but failed initialization (!alloc_tag_cttype or IS_ERR(alloc_tag_cttype)) In all cases, alloc_tag_cttype is not allocated, and therefore alloc_tag_top_users() should not attempt to acquire the semaphore. This leads to a crash on memory allocation failure by attempting to acquire a non-existent semaphore: Oops: general protection fault, probably for non-canonical address 0xdffffc000000001b: 0000 [#3] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x00000000000000d8-0x00000000000000df] CPU: 2 UID: 0 PID: 1 Comm: systemd Tainted: G D 6.16.0-rc2 #1 VOLUNTARY Tainted: [D]=DIE Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:down_read_trylock+0xaa/0x3b0 Code: d0 7c 08 84 d2 0f 85 a0 02 00 00 8b 0d df 31 dd 04 85 c9 75 29 48 b8 00 00 00 00 00 fc ff df 48 8d 6b 68 48 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 88 02 00 00 48 3b 5b 68 0f 85 53 01 00 00 65 ff RSP: 0000:ffff8881002ce9b8 EFLAGS: 00010016 RAX: dffffc0000000000 RBX: 0000000000000070 RCX: 0000000000000000 RDX: 000000000000001b RSI: 000000000000000a RDI: 0000000000000070 RBP: 00000000000000d8 R08: 0000000000000001 R09: ffffed107dde49d1 R10: ffff8883eef24e8b R11: ffff8881002cec20 R12: 1ffff11020059d37 R13: 00000000003fff7b R14: ffff8881002cec20 R15: dffffc0000000000 FS: 00007f963f21d940(0000) GS:ffff888458ca6000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f963f5edf71 CR3: 000000010672c000 CR4: 0000000000350ef0 Call Trace: <TASK> codetag_trylock_module_list+0xd/0x20 alloc_tag_top_users+0x369/0x4b0 __show_mem+0x1cd/0x6e0 warn_alloc+0x2b1/0x390 __alloc_frozen_pages_noprof+0x12b9/0x21a0 alloc_pages_mpol+0x135/0x3e0 alloc_slab_page+0x82/0xe0 new_slab+0x212/0x240 ___slab_alloc+0x82a/0xe00 </TASK> As David Wang points out, this issue became easier to trigger after commit 780138b12381 ("alloc_tag: check mem_profiling_support in alloc_tag_init"). Before the commit, the issue occurred only when it failed to allocate and initialize alloc_tag_cttype or if a memory allocation fails before alloc_tag_init() is called. After the commit, it can be easily triggered when memory profiling is compiled but disabled at boot. To properly determine whether alloc_tag_init() has been called and its data structures initialized, verify that alloc_tag_cttype is a valid pointer before acquiring the semaphore. If the variable is NULL or an error value, it has not been properly initialized. In such a case, just skip and do not attempt to acquire the semaphore. [[email protected]: v3]

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of service disruption.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2025-08-16 11:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 09:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 5.5 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2025-08-16 11:15 UTC

Last modified

2026-06-17 09:17 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-476 · NULL pointer dereference

Record status

Analyzed

Affected

• Linux Kernel < 6.12.39
• Linux Kernel < 6.15.7
• Linux Kernel 6.16

Attack profile CVSS 3.1 · 5.5

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2025-38517.md and follow it. Check whether this project is affected by CVE-2025-38517. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

Copy as ticket · More options · Status badge