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vuln-cve/data/2026/43xxx/CVE-2026-43420.json
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{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"cveMetadata": {
"cveId": "CVE-2026-43420",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2026-05-01T14:12:56.008Z",
"datePublished": "2026-05-08T14:21:55.717Z",
"dateUpdated": "2026-11-06T15:42:52.894Z"
},
"containers": {
"cna": {
"providerMetadata": {
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux",
"dateUpdated": "2026-05-11T22:24:14.623Z"
},
"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."
}
],
"affected": [
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"fs/ceph/dir.c"
],
"versions": [
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "6d5fd8bb574bef039eb3b738e523870433a2aeb9",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "fcc477a6e8856c8a42b3c9e171724d8d6dfadd06",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "aedd29386b23f3e1e6818943e11abfff2953732f",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "7db008e85a5d17b64bc5390b828bf457ae91a415",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "8975b85b0d45ca811ace6fac5907652f2310e5ac",
"status": "affected",
"versionType": "git"
},
{
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "ce0123cbb4a40a2f1bbb815f292b26e96088639f",
"status": "affected",
"versionType": "git"
}
]
},
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "affected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"fs/ceph/dir.c"
],
"versions": [
{
"version": "5.7",
"status": "affected"
},
{
"version": "0",
"lessThan": "5.7",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "5.10.253",
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "5.15.203",
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.1.167",
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.6.130",
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.12.78",
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.18.19",
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "6.19.9",
"lessThanOrEqual": "6.19.*",
"status": "unaffected",
"versionType": "semver"
},
{
"version": "7.0",
"lessThanOrEqual": "*",
"status": "unaffected",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"operator": "OR",
"negate": false,
"cpeMatch": [
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "5.10.253"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "5.15.203"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "6.1.167"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "6.6.130"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "6.12.78"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "6.18.19"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "6.19.9"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.7",
"versionEndExcluding": "7.0"
}
]
}
]
}
],
"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"
},
{
"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",
"x_generator": {
"engine": "bippy-1.2.0"
}
},
"adp": [
{
"metrics": [
{
"other": {
"type": "ssvc",
"content": {
"id": "CVE-2026-43420",
"role": "CISA Coordinator",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"version": "2.0.3",
"timestamp": "2026-11-06T15:37:58.335576Z"
}
}
}
],
"title": "CISA ADP Vulnrichment",
"providerMetadata": {
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP",
"dateUpdated": "2026-11-06T15:42:52.894Z"
}
}
]
}
}
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