CVE-2026-43420
📛 CVE Title
ceph: fix i_nlink underrun during async unlink
Description
In the Linux kernel, the following vulnerability has been resolved: ceph: fix i_nlink underrun during async unlink During async unlink, we drop the `i_nlink` counter before we receive the completion (that will eventually update the `i_nlink`) because "we assume that the unlink will succeed". That is not a bad idea, but it races against deletions by other clients (or against the completion of our own unlink) and can lead to an underrun which emits a WARNING like this one: WARNING: CPU: 85 PID: 25093 at fs/inode.c:407 drop_nlink+0x50/0x68 Modules linked in: CPU: 85 UID: 3221252029 PID: 25093 Comm: php-cgi8.1 Not tainted 6.14.11-cm4all1-ampere #655 Hardware name: Supermicro ARS-110M-NR/R12SPD-A, BIOS 1.1b 10/17/2023 pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : drop_nlink+0x50/0x68 lr : ceph_unlink+0x6c4/0x720 sp : ffff80012173bc90 x29: ffff80012173bc90 x28: ffff086d0a45aaf8 x27: ffff0871d0eb5680 x26: ffff087f2a64a718 x25: 0000020000000180 x24: 0000000061c88647 x23: 0000000000000002 x22: ffff07ff9236d800 x21: 0000000000001203 x20: ffff07ff9237b000 x19: ffff088b8296afc0 x18: 00000000f3c93365 x17: 0000000000070000 x16: ffff08faffcbdfe8 x15: ffff08faffcbdfec x14: 0000000000000000 x13: 45445f65645f3037 x12: 34385f6369706f74 x11: 0000a2653104bb20 x10: ffffd85f26d73290 x9 : ffffd85f25664f94 x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000002 x5 : 0000000000000081 x4 : 0000000000000481 x3 : 0000000000000000 x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff08727d3f91e8 Call trace: drop_nlink+0x50/0x68 (P) vfs_unlink+0xb0/0x2e8 do_unlinkat+0x204/0x288 __arm64_sys_unlinkat+0x3c/0x80 invoke_syscall.constprop.0+0x54/0xe8 do_el0_svc+0xa4/0xc8 el0_svc+0x18/0x58 el0t_64_sync_handler+0x104/0x130 el0t_64_sync+0x154/0x158 In ceph_unlink(), a call to ceph_mdsc_submit_request() submits the CEPH_MDS_OP_UNLINK to the MDS, but does not wait for completion. Meanwhile, between this call and the following drop_nlink() call, a worker thread may process a CEPH_CAP_OP_IMPORT, CEPH_CAP_OP_GRANT or just a CEPH_MSG_CLIENT_REPLY (the latter of which could be our own completion). These will lead to a set_nlink() call, updating the `i_nlink` counter to the value received from the MDS. If that new `i_nlink` value happens to be zero, it is illegal to decrement it further. But that is exactly what ceph_unlink() will do then. The WARNING can be reproduced this way: 1. Force async unlink; only the async code path is affected. Having no real clue about Ceph internals, I was unable to find out why the MDS wouldn't give me the "Fxr" capabilities, so I patched get_caps_for_async_unlink() to always succeed. (Note that the WARNING dump above was found on an unpatched kernel, without this kludge - this is not a theoretical bug.) 2. Add a sleep call after ceph_mdsc_submit_request() so the unlink completion gets handled by a worker thread before drop_nlink() is called. This guarantees that the `i_nlink` is already zero before drop_nlink() runs. The solution is to skip the counter decrement when it is already zero, but doing so without a lock is still racy (TOCTOU). Since ceph_fill_inode() and handle_cap_grant() both hold the `ceph_inode_info.i_ceph_lock` spinlock while set_nlink() runs, this seems like the proper lock to protect the `i_nlink` updates. I found prior art in NFS and SMB (using `inode.i_lock`) and AFS (using `afs_vnode.cb_lock`). All three have the zero check as well.
Overview
- State
- PUBLISHED
- Assigner (CNA)
- Linux
- CVSS severity
- medium
- CVSS score
- 5.5 / 10
- CVSS vector
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H- Effective score
- 5.5 / 10 MEDIUM source: CNA overview
- CWE(s)
- —
- Reserved
- 2026-05-01
- Published
- 2026-05-08 16:21 UTC
- Last updated
- 2026-05-12 00:24 UTC
- Source
- https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/43xxx/CVE-2026-43420.json
- Linked Threat
- CVE-2026-43420 — CVE-2026-43420
NVD triage scoring NVD CVE 2.0
Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.
- NVD published
- 2026-05-08 15:16:54 UTC
- NVD last modified
- 2026-05-12 14:10:27 UTC
- EPSS score
- 0.0003 (probability of exploitation in next 30 days)
- EPSS percentile
- 9.59% vs all CVEs — higher = more likely to be exploited, as of 2026-05-24
NVD / KEV / EPSS data refreshed 2026-05-25 08:54 UTC. Re-run the 🛰 Backfill from NVD button above to refresh.
European Union Vulnerability Database ENISA EUVD
ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.
- EUVD ID
-
EUVD-2026-28726 - Assigner
- Linux
- Published
- May 8, 2026, 2:21:55 PM
- Updated
- May 11, 2026, 10:24:14 PM
- EUVD base score
- 0.0 / 10
- EUVD-reported EPSS
- 0.0100
- Vendors
- Linux
- Products
-
Linux (patch: 6.12.78)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <6d5fd8bb574bef039eb3b738e523870433a2aeb9)Linux (patch: 7.0)Linux (patch: 5.15.203)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <8975b85b0d45ca811ace6fac5907652f2310e5ac)Linux (patch: 0)Linux (patch: 6.18.19)Linux (patch: 6.6.130)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <ce0123cbb4a40a2f1bbb815f292b26e96088639f)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <aedd29386b23f3e1e6818943e11abfff2953732f)Linux (5.7)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <fcc477a6e8856c8a42b3c9e171724d8d6dfadd06)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c)Linux (patch: 6.19.9)Linux (patch: 5.10.253)Linux (patch: 6.1.167)Linux (2ccb45462aeaf0831397b90d31d3d50a7704fa1f <7db008e85a5d17b64bc5390b828bf457ae91a415)
ENISA description: In the Linux kernel, the following vulnerability has been resolved: ceph: fix i_nlink underrun during async unlink During async unlink, we drop the `i_nlink` counter before we receive the completion (that will eventually update the `i_nlink`) because "we assume that the unlink will succeed". That is not a bad idea, but it races against deletions by other clients (or against the completion of our own unlink) and can lead to an underrun which emits a WARNING like this one: WARNING: CPU: 85 PID: 25093 at fs/inode.c:407 drop_nlink+0x50/0x68 Modules linked in: CPU: 85 UID: 3221252029 PID: 25093 Comm: php-cgi8.1 Not tainted 6.14.11-cm4all1-ampere #655 Hardware name: Supermicro ARS-110M-NR/R12SPD-A, BIOS 1.1b 10/17/2023 pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : drop_nlink+0x50/0x68 lr : ceph_unlink+0x6c4/0x720 sp : ffff80012173bc90 x29: ffff80012173bc90 x28: ffff086d0a45aaf8 x27: ffff0871d0eb5680 x26: ffff087f2a64a718 x25: 0000020000000180 x24: 0000000061c88647 x23: 0000000000000002 x22: ffff07ff9236d800 x21: 0000000000001203 x20: ffff07ff9237b000 x19: ffff088b8296afc0 x18: 00000000f3c93365 x17: 0000000000070000 x16: ffff08faffcbdfe8 x15: ffff08faffcbdfec x14: 0000000000000000 x13: 45445f65645f3037 x12: 34385f6369706f74 x11: 0000a2653104bb20 x10: ffffd85f26d73290 x9 : ffffd85f25664f94 x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000002 x5 : 0000000000000081 x4 : 0000000000000481 x3 : 0000000000000000 x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff08727d3f91e8 Call trace: drop_nlink+0x50/0x68 (P) vfs_unlink+0xb0/0x2e8 do_unlinkat+0x204/0x288 __arm64_sys_unlinkat+0x3c/0x80 invoke_syscall.constprop.0+0x54/0xe8 do_el0_svc+0xa4/0xc8 el0_svc+0x18/0x58 el0t_64_sync_handler+0x104/0x130 el0t_64_sync+0x154/0x158 In ceph_unlink(), a call to ceph_mdsc_submit_request() submits the CEPH_MDS_OP_UNLINK to the MDS, but does not wait for completion. Meanwhile, between this call and the following drop_nlink() call, a worker thread may process a CEPH_CAP_OP_IMPORT, CEPH_CAP_OP_GRANT or just a CEPH_MSG_CLIENT_REPLY (the latter of which could be our own completion). These will lead to a set_nlink() call, updating the `i_nlink` counter to the value received from the MDS. If that new `i_nlink` value happens to be zero, it is illegal to decrement it further. But that is exactly what ceph_unlink() will do then. The WARNING can be reproduced this way: 1. Force async unlink; only the async code path is affected. Having no real clue about Ceph internals, I was unable to find out why the MDS wouldn't give me the "Fxr" capabilities, so I patched get_caps_for_async_unlink() to always succeed. (Note that the WARNING dump above was found on an unpatched kernel, without this kludge - this is not a theoretical bug.) 2. Add a sleep call after ceph_mdsc_submit_request() so the unlink completion gets handled by a worker thread before drop_nlink() is called. This guarantees that the `i_nlink` is already zero before drop_nlink() runs. The solution is to skip the counter decrement when it is already zero, but doing so without a lock is still racy (TOCTOU). Since ceph_fill_inode() and handle_cap_grant() both hold the `ceph_inode_info.i_ceph_lock` spinlock while set_nlink() runs, this seems like the proper lock to protect the `i_nlink` updates. I found prior art in NFS and SMB (using `inode.i_lock`) and AFS (using `afs_vnode.cb_lock`). All three have the zero check as well.
EUVD references (8)
- https://git.kernel.org/stable/c/9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c
- https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9
- https://git.kernel.org/stable/c/fcc477a6e8856c8a42b3c9e171724d8d6dfadd06
- https://git.kernel.org/stable/c/b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859
- https://git.kernel.org/stable/c/aedd29386b23f3e1e6818943e11abfff2953732f
- https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415
- https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac
- https://git.kernel.org/stable/c/ce0123cbb4a40a2f1bbb815f292b26e96088639f
Affected products (2)
| Vendor | Product | Versions | Platforms |
|---|---|---|---|
| Linux | Linux |
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected),
2ccb45462aeaf0831397b90d31d3d50a7704fa1f (affected)
|
— |
| Linux | Linux |
5.7 (affected),
0 (unaffected),
5.10.253 (unaffected),
5.15.203 (unaffected),
6.1.167 (unaffected),
6.6.130 (unaffected),
6.12.78 (unaffected),
6.18.19 (unaffected),
6.19.9 (unaffected),
7.0 (unaffected)
|
— |
Vendor references (8)
References embedded in the original CVE record by the assigning CNA.
- https://git.kernel.org/stable/c/9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c
- https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9
- https://git.kernel.org/stable/c/fcc477a6e8856c8a42b3c9e171724d8d6dfadd06
- https://git.kernel.org/stable/c/b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859
- https://git.kernel.org/stable/c/aedd29386b23f3e1e6818943e11abfff2953732f
- https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415
- https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac
- https://git.kernel.org/stable/c/ce0123cbb4a40a2f1bbb815f292b26e96088639f
MITRE references (8) cveawg.mitre.org
Pulled from MITRE's CVE Services API by the 🛰 Backfill from MITRE button.
- https://git.kernel.org/stable/c/9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c
- https://git.kernel.org/stable/c/aedd29386b23f3e1e6818943e11abfff2953732f
- https://git.kernel.org/stable/c/b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859
- https://git.kernel.org/stable/c/ce0123cbb4a40a2f1bbb815f292b26e96088639f
- https://git.kernel.org/stable/c/fcc477a6e8856c8a42b3c9e171724d8d6dfadd06
- https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9
- https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415
- https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac
Web references (5)
DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.
- https://attackerkb.com/topics/CVE-2026-43420 rapid7:attackerkb.com
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-28726 rapid7:euvd.enisa.europa.eu
- https://www.first.org/epss/ tenable:www.first.org
- https://nvd.nist.gov/vuln/detail/CVE-2026-43420 tenable:nvd.nist.gov
- https://www.cve.org/CVERecord?id=CVE-2026-43420 tenable:www.cve.org
NVD-tagged references (8)
Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.
- https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/aedd29386b23f3e1e6818943e11abfff2953732f 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/ce0123cbb4a40a2f1bbb815f292b26e96088639f 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- https://git.kernel.org/stable/c/fcc477a6e8856c8a42b3c9e171724d8d6dfadd06 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Remediations (17)
Remediations are stored against the linked Threat row; the list below is deduplicated across both pages.
-
web:blog.qualys.com
With Qualys Policy Audit's out-of-the-box mitigation or Compensatory Controls, which reduce the risk of a vulnerability being exploited because the remediation ( fix / patch ) cannot be done immediately, these security controls are not recommended by any industry standards, such as CIS and DISA-STIG.
2026-05-23 21:05 UTC -
web:cyberpress.org
The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added two actively exploited Microsoft Defender vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog, issuing an urgent remediation directive for federal agencies with a due date of June 3, 2026 .
2026-05-23 21:05 UTC -
web:krebsonsecurity.com
Microsoft today pushed software updates to fix a staggering 167 security vulnerabilities in its Windows operating systems and related software, including a SharePoint Server zero-day and a ...
2026-05-23 21:05 UTC -
web:oradba.ch
19c 26ai cve oracle-cpu patch -management release-update security Oracle CPU April 2026 : Delayed RUs & First Analysis On April 21, 2026 , Oracle released the Critical Patch Update (CPU) for April 2026 — 481 new security fixes across the entire Oracle product stack. For Oracle Database, this means another round of mandatory patching.
2026-05-23 21:05 UTC -
web:portal.msrc.microsoft.com
The Security Update Guide provides information on the latest Microsoft security updates, helping users understand and address potential vulnerabilities effectively.
2026-05-23 21:05 UTC -
web:www.crowdstrike.com
Microsoft's April 2026 Patch Tuesday addresses 164 CVEs , featuring 8 Critical vulnerabilities, one exploited zero-day, and one disclosed zero-day.
2026-05-23 21:05 UTC -
web:www.oracle.com
This Critical Patch Update contains 481 new security patches across the product families listed below. Please note that an MOS note summarizing the content of this Critical Patch Update and other Oracle Software Security Assurance activities is located at April 2026 Critical Patch Update: Executive Summary and Analysis.
2026-05-23 21:05 UTC -
web:www.picussecurity.com
CVE - 2026 -41940 explained: how a CRLF injection bypassed cPanel & WHM authentication on 1.5M servers. Root cause, exploit chain, IOCs, and patch guidance.
2026-05-23 21:05 UTC -
web:www.techrepublic.com
Microsoft's April 2026 Patch Tuesday fixes 165 vulnerabilities, including two zero-days, in one of the company's largest monthly security updates.
2026-05-23 21:05 UTC -
web:www.windowslatest.com
Windows 11 April 2026 update adds Narrator Copilot support, faster Settings, File Explorer fixes, and key security improvements.
2026-05-23 21:05 UTC -
web:blog.talosintelligence.com
Microsoft has released its monthly security update for April 2026 , which includes 165 vulnerabilities affecting a wide range of products, including eight Microsoft marked as "critical." CVE - 2026 -23666 is a critical Denial of Service (DoS) vulnerability that affects the .NET framework. Successful exploitation could allow the attacker to deny service over the network. CVE - 2026 -32157 is a ...
2026-06-03 22:29 UTC -
web:blogs.oracle.com
For more information about the Critical Patch Update program, see the security vulnerability remediation practices page located on the Oracle Trust Center.
2026-06-03 22:29 UTC -
web:carthageelectronics.com
Status: Actively exploited — CISA KEV listed — patch by May 12, 2026 What Happened On April 28, 2026 , CISA added CVE - 2026 -32202 to its Known Exploited Vulnerabilities (KEV) catalog with a federal remediation deadline of May 12, 2026 . This vulnerability is the result of an incomplete patch Microsoft released in February for CVE - 2026 -21510.
2026-06-03 22:29 UTC -
web:msrc.microsoft.com
Access Microsoft Security Response Center's guide to address vulnerabilities, manage security risks, and keep your systems protected with the latest updates.
2026-06-03 22:29 UTC -
web:threatprotect.qualys.com
With Qualys Policy Audit's out-of-the-box mitigation or Compensatory Controls, which reduce the risk of a vulnerability being exploited because the remediation ( fix / patch ) cannot be done immediately, these security controls are not recommended by any industry standards, such as CIS and DISA-STIG.
2026-06-03 22:29 UTC -
web:www.malwarebytes.com
This month's Patch Tuesday addresses 167 vulnerabilities, including two zero-days that could lead to system compromise, data exposure, and privilege escalation.
2026-06-03 22:29 UTC -
web:zecurit.com
Get the complete breakdown of Microsoft's June 2026 Patch Tuesday. We analyze the latest security updates and all critical CVEs .
2026-06-03 22:29 UTC
AI Forensic Analysis
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Raw JSON
The full cvelistV5 record. Download as CVE-2026-43420.json.
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/ceph/dir.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "6d5fd8bb574bef039eb3b738e523870433a2aeb9",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "fcc477a6e8856c8a42b3c9e171724d8d6dfadd06",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "aedd29386b23f3e1e6818943e11abfff2953732f",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "7db008e85a5d17b64bc5390b828bf457ae91a415",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "8975b85b0d45ca811ace6fac5907652f2310e5ac",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
},
{
"lessThan": "ce0123cbb4a40a2f1bbb815f292b26e96088639f",
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/ceph/dir.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "5.7"
},
{
"lessThan": "5.7",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.253",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.203",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.167",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix i_nlink underrun during async unlink\n\nDuring async unlink, we drop the `i_nlink` counter before we receive\nthe completion (that will eventually update the `i_nlink`) because \"we\nassume that the unlink will succeed\". That is not a bad idea, but it\nraces against deletions by other clients (or against the completion of\nour own unlink) and can lead to an underrun which emits a WARNING like\nthis one:\n\n WARNING: CPU: 85 PID: 25093 at fs/inode.c:407 drop_nlink+0x50/0x68\n Modules linked in:\n CPU: 85 UID: 3221252029 PID: 25093 Comm: php-cgi8.1 Not tainted 6.14.11-cm4all1-ampere #655\n Hardware name: Supermicro ARS-110M-NR/R12SPD-A, BIOS 1.1b 10/17/2023\n pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)\n pc : drop_nlink+0x50/0x68\n lr : ceph_unlink+0x6c4/0x720\n sp : ffff80012173bc90\n x29: ffff80012173bc90 x28: ffff086d0a45aaf8 x27: ffff0871d0eb5680\n x26: ffff087f2a64a718 x25: 0000020000000180 x24: 0000000061c88647\n x23: 0000000000000002 x22: ffff07ff9236d800 x21: 0000000000001203\n x20: ffff07ff9237b000 x19: ffff088b8296afc0 x18: 00000000f3c93365\n x17: 0000000000070000 x16: ffff08faffcbdfe8 x15: ffff08faffcbdfec\n x14: 0000000000000000 x13: 45445f65645f3037 x12: 34385f6369706f74\n x11: 0000a2653104bb20 x10: ffffd85f26d73290 x9 : ffffd85f25664f94\n x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000002\n x5 : 0000000000000081 x4 : 0000000000000481 x3 : 0000000000000000\n x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff08727d3f91e8\n Call trace:\n drop_nlink+0x50/0x68 (P)\n vfs_unlink+0xb0/0x2e8\n do_unlinkat+0x204/0x288\n __arm64_sys_unlinkat+0x3c/0x80\n invoke_syscall.constprop.0+0x54/0xe8\n do_el0_svc+0xa4/0xc8\n el0_svc+0x18/0x58\n el0t_64_sync_handler+0x104/0x130\n el0t_64_sync+0x154/0x158\n\nIn ceph_unlink(), a call to ceph_mdsc_submit_request() submits the\nCEPH_MDS_OP_UNLINK to the MDS, but does not wait for completion.\n\nMeanwhile, between this call and the following drop_nlink() call, a\nworker thread may process a CEPH_CAP_OP_IMPORT, CEPH_CAP_OP_GRANT or\njust a CEPH_MSG_CLIENT_REPLY (the latter of which could be our own\ncompletion). These will lead to a set_nlink() call, updating the\n`i_nlink` counter to the value received from the MDS. If that new\n`i_nlink` value happens to be zero, it is illegal to decrement it\nfurther. But that is exactly what ceph_unlink() will do then.\n\nThe WARNING can be reproduced this way:\n\n1. Force async unlink; only the async code path is affected. Having\n no real clue about Ceph internals, I was unable to find out why the\n MDS wouldn't give me the \"Fxr\" capabilities, so I patched\n get_caps_for_async_unlink() to always succeed.\n\n (Note that the WARNING dump above was found on an unpatched kernel,\n without this kludge - this is not a theoretical bug.)\n\n2. Add a sleep call after ceph_mdsc_submit_request() so the unlink\n completion gets handled by a worker thread before drop_nlink() is\n called. This guarantees that the `i_nlink` is already zero before\n drop_nlink() runs.\n\nThe solution is to skip the counter decrement when it is already zero,\nbut doing so without a lock is still racy (TOCTOU). Since\nceph_fill_inode() and handle_cap_grant() both hold the\n`ceph_inode_info.i_ceph_lock` spinlock while set_nlink() runs, this\nseems like the proper lock to protect the `i_nlink` updates.\n\nI found prior art in NFS and SMB (using `inode.i_lock`) and AFS (using\n`afs_vnode.cb_lock`). All three have the zero check as well."
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"providerMetadata": {
"dateUpdated": "2026-05-11T22:24:14.623Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"references": [
{
"url": "https://git.kernel.org/stable/c/9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c"
},
{
"url": "https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9"
},
{
"url": "https://git.kernel.org/stable/c/fcc477a6e8856c8a42b3c9e171724d8d6dfadd06"
},
{
"url": "https://git.kernel.org/stable/c/b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859"
},
{
"url": "https://git.kernel.org/stable/c/aedd29386b23f3e1e6818943e11abfff2953732f"
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{
"url": "https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415"
},
{
"url": "https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac"
},
{
"url": "https://git.kernel.org/stable/c/ce0123cbb4a40a2f1bbb815f292b26e96088639f"
}
],
"title": "ceph: fix i_nlink underrun during async unlink",
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"assignerShortName": "Linux",
"cveId": "CVE-2026-43420",
"datePublished": "2026-05-08T14:21:55.717Z",
"dateReserved": "2026-05-01T14:12:56.008Z",
"dateUpdated": "2026-05-11T22:24:14.623Z",
"state": "PUBLISHED"
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