GHSA-F2Q5-7Q65-XQX7
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-14 15:32In the Linux kernel, the following vulnerability has been resolved:
NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check
The header for commit e75b23f9e323 ("nfsd: check d_can_lookup in fh_verify of directories") details the assumption that justified adding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is invalid (in the case of NFS reexport).
When NFSD exports an NFS filesystem it is very possible for nfsd_mode_check() to encounter a @dentry that doesn't have i_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and NFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()).
So remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir return on that branch must stay. It guards the subsequent lookup_one_unlocked() -> __lookup_slow() path, which calls inode->i_op->lookup() with no NULL check, so returning nfserr_notdir is what keeps a client LOOKUP into such a @dentry from dereferencing a NULL method pointer.
{
"affected": [],
"aliases": [
"CVE-2026-89711"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:19:58Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check\n\nThe header for commit e75b23f9e323 (\"nfsd: check d_can_lookup in\nfh_verify of directories\") details the assumption that justified\nadding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is\ninvalid (in the case of NFS reexport).\n\nWhen NFSD exports an NFS filesystem it is very possible for\nnfsd_mode_check() to encounter a @dentry that doesn\u0027t have\ni_op-\u003elookup (see nfs_fhget()\u0027s NFS_ATTR_FATTR_MOUNTPOINT and\nNFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()).\n\nSo remove nfsd_mode_check()\u0027s WARN_ON_ONCE(). The nfserr_notdir\nreturn on that branch must stay. It guards the subsequent\nlookup_one_unlocked() -\u003e __lookup_slow() path, which calls\ninode-\u003ei_op-\u003elookup() with no NULL check, so returning nfserr_notdir\nis what keeps a client LOOKUP into such a @dentry from dereferencing\na NULL method pointer.",
"id": "GHSA-f2q5-7q65-xqx7",
"modified": "2026-09-14T15:32:34Z",
"published": "2026-09-11T21:31:37Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89711"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2ef131323999539038e306773c8256403834361b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7ef182a8fe9c12b0d936880b1e504840639aa009"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9f4434893a2783f7384d993cea883aff3fb7a52d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a275de3bac5635514ca830f2e46b5ff0e66b5c4c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ae251937c6f0237e5b555a5e4ba4595b8206e865"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b55b4d880bb080fa10eb08ba21a5d8679b8102fe"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e145e8d67a5d41c72d322e7f87ab474d39d9dfb7"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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