GHSA-WWVQ-J7G5-3QRF
Vulnerability from github – Published: 2026-04-22 15:31 – Updated: 2026-07-14 15:31In the Linux kernel, the following vulnerability has been resolved:
ext4: fix use-after-free in update_super_work when racing with umount
Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups reads during unmount. However, this introduced a use-after-free because update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which accesses the kobject's kernfs_node after it has been freed by kobject_del() in ext4_unregister_sysfs():
update_super_work ext4_put_super ----------------- -------------- ext4_unregister_sysfs(sb) kobject_del(&sbi->s_kobj) __kobject_del() sysfs_remove_dir() kobj->sd = NULL sysfs_put(sd) kernfs_put() // RCU free ext4_notify_error_sysfs(sbi) sysfs_notify(&sbi->s_kobj) kn = kobj->sd // stale pointer kernfs_get(kn) // UAF on freed kernfs_node ext4_journal_destroy() flush_work(&sbi->s_sb_upd_work)
Instead of reordering the teardown sequence, fix this by making ext4_notify_error_sysfs() detect that sysfs has already been torn down by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call in that case. A dedicated mutex (s_error_notify_mutex) serializes ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs() to prevent TOCTOU races where the kobject could be deleted between the state_in_sysfs check and the sysfs_notify() call.
{
"affected": [],
"aliases": [
"CVE-2026-31446"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-04-22T14:16:38Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: fix use-after-free in update_super_work when racing with umount\n\nCommit b98535d09179 (\"ext4: fix bug_on in start_this_handle during umount\nfilesystem\") moved ext4_unregister_sysfs() before flushing s_sb_upd_work\nto prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups\nreads during unmount. However, this introduced a use-after-free because\nupdate_super_work calls ext4_notify_error_sysfs() -\u003e sysfs_notify() which\naccesses the kobject\u0027s kernfs_node after it has been freed by kobject_del()\nin ext4_unregister_sysfs():\n\n update_super_work ext4_put_super\n ----------------- --------------\n ext4_unregister_sysfs(sb)\n kobject_del(\u0026sbi-\u003es_kobj)\n __kobject_del()\n sysfs_remove_dir()\n kobj-\u003esd = NULL\n sysfs_put(sd)\n kernfs_put() // RCU free\n ext4_notify_error_sysfs(sbi)\n sysfs_notify(\u0026sbi-\u003es_kobj)\n kn = kobj-\u003esd // stale pointer\n kernfs_get(kn) // UAF on freed kernfs_node\n ext4_journal_destroy()\n flush_work(\u0026sbi-\u003es_sb_upd_work)\n\nInstead of reordering the teardown sequence, fix this by making\next4_notify_error_sysfs() detect that sysfs has already been torn down\nby checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call\nin that case. A dedicated mutex (s_error_notify_mutex) serializes\next4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()\nto prevent TOCTOU races where the kobject could be deleted between the\nstate_in_sysfs check and the sysfs_notify() call.",
"id": "GHSA-wwvq-j7g5-3qrf",
"modified": "2026-07-14T15:31:51Z",
"published": "2026-04-22T15:31:40Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31446"
},
{
"type": "WEB",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
},
{
"type": "WEB",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-082556.html"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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