CVE-2026-43420
Estado: AnalizadaMedia (4.7)—
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:
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.
Leer descripción completaMostrar menos
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:
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.
Detalles técnicos trazas, registros y código del informe original
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 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.
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 4.7
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.11%
- Percentil entre todas las CVEs puntuadas: 1
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (1)
CWE
- CWE-367
Referencias
- https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9
- https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415
- https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac
- 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
JSON original (NVD)
Mostrar
{
"id": "CVE-2026-43420",
"cveTags": [],
"metrics": {
"cvssMetricV31": [
{
"type": "Primary",
"source": "nvd@nist.gov",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 4.7,
"attackVector": "LOCAL",
"baseSeverity": "MEDIUM",
"vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
"integrityImpact": "NONE",
"userInteraction": "NONE",
"attackComplexity": "HIGH",
"availabilityImpact": "HIGH",
"privilegesRequired": "LOW",
"confidentialityImpact": "NONE"
},
"impactScore": 3.6,
"exploitabilityScore": 1
}
]
},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "6d5fd8bb574bef039eb3b738e523870433a2aeb9",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "fcc477a6e8856c8a42b3c9e171724d8d6dfadd06",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "aedd29386b23f3e1e6818943e11abfff2953732f",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "7db008e85a5d17b64bc5390b828bf457ae91a415",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "8975b85b0d45ca811ace6fac5907652f2310e5ac",
"versionType": "git"
},
{
"status": "affected",
"version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f",
"lessThan": "ce0123cbb4a40a2f1bbb815f292b26e96088639f",
"versionType": "git"
}
],
"programFiles": [
"fs/ceph/dir.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "5.7"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "5.7",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.253",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.203",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.167",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.130",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.78",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.19",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "6.19.9",
"versionType": "semver",
"lessThanOrEqual": "6.19.*"
},
{
"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"fs/ceph/dir.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-05-08T15:16:54.023",
"references": [
{
"url": "https://git.kernel.org/stable/c/6d5fd8bb574bef039eb3b738e523870433a2aeb9",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/7db008e85a5d17b64bc5390b828bf457ae91a415",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/8975b85b0d45ca811ace6fac5907652f2310e5ac",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/aedd29386b23f3e1e6818943e11abfff2953732f",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/ce0123cbb4a40a2f1bbb815f292b26e96088639f",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/fcc477a6e8856c8a42b3c9e171724d8d6dfadd06",
"tags": [
"Patch"
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Analyzed",
"weaknesses": [
{
"type": "Primary",
"source": "nvd@nist.gov",
"description": [
{
"lang": "en",
"value": "CWE-367"
}
]
}
],
"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."
}
],
"lastModified": "2026-06-17T10:49:33.837",
"configurations": [
{
"nodes": [
{
"negate": false,
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "0B1A046E-0C62-426C-8D6D-9BCC6EB56D6E",
"versionEndExcluding": "5.10.253",
"versionStartIncluding": "5.7"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045",
"versionEndExcluding": "5.15.203",
"versionStartIncluding": "5.11"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "2EDC6BAF-B710-4E26-B6AA-D68922EE7B43",
"versionEndExcluding": "6.1.167",
"versionStartIncluding": "5.16"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "C57BB918-DF28-46B3-94F7-144176841267",
"versionEndExcluding": "6.6.130",
"versionStartIncluding": "6.2"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "28D591F5-B196-4CC9-905C-DC80F116E7A8",
"versionEndExcluding": "6.12.78",
"versionStartIncluding": "6.7"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "D394AC60-6F28-435F-872A-CCDF384B8331",
"versionEndExcluding": "6.18.19",
"versionStartIncluding": "6.13"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "E825E7C3-FEAC-4FD3-8A81-78D7387948C9",
"versionEndExcluding": "6.19.9",
"versionStartIncluding": "6.19"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"
}
],
"operator": "OR"
}
]
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}