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CVE Record

CVE-2025-38517: lib/alloc_tag: do not acquire non-existent lock in alloc_tag_top_users()

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. [harry.yoo@oracle.com: v3]

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-38517 is a Linux kernel bug that can crash a system when memory allocation fails and the kernel tries to inspect allocation tag users before required data structures exist. The available sources describe a reliability and availability issue, not data theft or code execution.

Executive priority

Handle this through normal kernel patch management with elevated attention for reliability-sensitive systems. There is no cited evidence of active exploitation, but a kernel crash can still disrupt production workloads.

Technical view

In alloc_tag_top_users(), the kernel may call codetag_trylock_module_list() on alloc_tag_cttype->mod_lock when alloc_tag_cttype is NULL or an error pointer. This can cause a general protection fault during memory allocation failure paths, especially when memory profiling is compiled in but disabled at boot.

Likely exposure

Exposure is most relevant to systems running affected Linux kernel versions listed in the CVE record, including 6.10, 6.12.39, 6.15.7, and 6.16. Downstream distribution status may differ because vendors backport kernel fixes.

Exploitation context

The source bundle does not cite active exploitation, and KEV is false. The described trigger involves kernel memory allocation failure paths and allocation tagging or memory profiling initialization state, resulting in a crash rather than a documented privilege escalation.

Researcher notes

The fix direction is to validate alloc_tag_cttype before acquiring its semaphore and skip processing when it is NULL or an error pointer. The CVE evidence is strong for root cause and crash behavior, but incomplete for exploitability, CVSS, and downstream package status.

Mitigation direction

  • Check your Linux distribution advisory for CVE-2025-38517 status.
  • Apply the vendor kernel update that includes the referenced stable fixes.
  • Prioritize hosts using affected upstream kernel versions or custom kernels.
  • Avoid treating this as remediated solely by package version strings.
  • Monitor critical systems for unexplained kernel oops or crash events.

Validation and detection

  • Inventory running kernel versions across servers and appliances.
  • Map each kernel to vendor advisories or upstream stable fix commits.
  • Review boot configuration for memory profiling and allocation tagging settings.
  • Check kernel logs for alloc_tag_top_users or down_read_trylock crashes.
  • Confirm patched kernels are active after reboot.
Prepared
Confidence
high
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
4Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

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Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux1438d349d16b78d88f9e978a4a5496f078c8191b, 1438d349d16b78d88f9e978a4a5496f078c8191b, 1438d349d16b78d88f9e978a4a5496f078c8191bunaffected
LinuxLinux6.10, 0, 6.12.39, 6.15.7, 6.16affected
Weakness

CWE details

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