GHSA-WR3H-QP2H-X6VF
Vulnerability from github – Published: 2026-09-04 18:31 – Updated: 2026-09-04 18:31In the Linux kernel, the following vulnerability has been resolved:
ext4: stop retrying saturated xattr cache entries
ext4_xattr_block_set() retries when a cache entry selected for reuse has a saturated reference count after taking the buffer lock. The retry returns to the mbcache lookup without making that entry ineligible, so it can select the same unusable entry indefinitely. A task spinning there can hold the parent directory's i_rwsem and leave concurrent rmdir callers blocked.
Normally a reusable entry has a reference count below EXT4_XATTR_REFCOUNT_MAX because the count and MBE_REUSABLE_B are updated under the same buffer lock. A corrupted filesystem can violate that invariant. The syzbot reproducer reports allocator and xattr corruption before triggering this retry loop.
Check the untrusted on-disk count before incrementing it, avoiding overflow, and clear MBE_REUSABLE_B when it is already saturated. The next lookup then skips the entry that was just proven unusable. This mirrors the normal transition at EXT4_XATTR_REFCOUNT_MAX; the release path marks the entry reusable again on the exact 1024-to-1023 transition.
Using the same QEMU harness and guest parameters, current unpatched Linux hung in 6 of 8 420-second trials with the do_rmdir signature; representative NMI backtraces caught the owner spinning in ext4_xattr_block_set(). The patched kernel completed 28 of 28 trials without a hung-task report; the final twelve trials exercised the reviewed overflow-safe form of the change. syzbot's patch testing also completed without reproducing the hang.
{
"affected": [],
"aliases": [
"CVE-2026-80808"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-04T16:18:07Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: stop retrying saturated xattr cache entries\n\next4_xattr_block_set() retries when a cache entry selected for reuse\nhas a saturated reference count after taking the buffer lock. The retry\nreturns to the mbcache lookup without making that entry ineligible, so\nit can select the same unusable entry indefinitely. A task spinning\nthere can hold the parent directory\u0027s i_rwsem and leave concurrent\nrmdir callers blocked.\n\nNormally a reusable entry has a reference count below\nEXT4_XATTR_REFCOUNT_MAX because the count and MBE_REUSABLE_B are\nupdated under the same buffer lock. A corrupted filesystem can violate\nthat invariant. The syzbot reproducer reports allocator and xattr\ncorruption before triggering this retry loop.\n\nCheck the untrusted on-disk count before incrementing it, avoiding\noverflow, and clear MBE_REUSABLE_B when it is already saturated. The\nnext lookup then skips the entry that was just proven unusable. This\nmirrors the normal transition at EXT4_XATTR_REFCOUNT_MAX; the release\npath marks the entry reusable again on the exact 1024-to-1023\ntransition.\n\nUsing the same QEMU harness and guest parameters, current unpatched\nLinux hung in 6 of 8 420-second trials with the do_rmdir signature;\nrepresentative NMI backtraces caught the owner spinning in\next4_xattr_block_set(). The patched kernel completed 28 of 28 trials\nwithout a hung-task report; the final twelve trials exercised the\nreviewed overflow-safe form of the change. syzbot\u0027s patch testing also\ncompleted without reproducing the hang.",
"id": "GHSA-wr3h-qp2h-x6vf",
"modified": "2026-09-04T18:31:27Z",
"published": "2026-09-04T18:31:27Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80808"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/119a2f053242ed75bdd2ebc95baf3ae7db6ccacf"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4902a5cba21aeaf91e6b29e20e0967a5f6abdcd9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/54b6bd40898de7906acb2bccc9a96d1b8e6b4323"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/55ee6533c1db7f7656fa8dd19637f3f8b8c08dc5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/61631352a5b405c89be579de00903b72e6888aa4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8865cd664484517703df5c18a965dc3227572b87"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/889ec86464d261f026f6c334040cfc6c58c99d58"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a40c45268f4358207aa9c53764fed2e05f62986a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dbd4aea175ad3c46436acb251e817b4374628072"
}
],
"schema_version": "1.4.0",
"severity": []
}
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