GHSA-7JWJ-6G7W-4C9Q
Vulnerability from github – Published: 2025-05-01 15:31 – Updated: 2025-11-10 21:30In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix use-after-free bug of ns_writer on remount
If a nilfs2 filesystem is downgraded to read-only due to metadata corruption on disk and is remounted read/write, or if emergency read-only remount is performed, detaching a log writer and synchronizing the filesystem can be done at the same time.
In these cases, use-after-free of the log writer (hereinafter nilfs->ns_writer) can happen as shown in the scenario below:
Task1 Task2 -------------------------------- ------------------------------ nilfs_construct_segment nilfs_segctor_sync init_wait init_waitqueue_entry add_wait_queue schedule nilfs_remount (R/W remount case) nilfs_attach_log_writer nilfs_detach_log_writer nilfs_segctor_destroy kfree finish_wait _raw_spin_lock_irqsave __raw_spin_lock_irqsave do_raw_spin_lock debug_spin_lock_before <-- use-after-free
While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1 waked up, Task1 accesses nilfs->ns_writer which is already freed. This scenario diagram is based on the Shigeru Yoshida's post [1].
This patch fixes the issue by not detaching nilfs->ns_writer on remount so that this UAF race doesn't happen. Along with this change, this patch also inserts a few necessary read-only checks with superblock instance where only the ns_writer pointer was used to check if the filesystem is read-only.
{
"affected": [],
"aliases": [
"CVE-2022-49834"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-05-01T15:16:06Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnilfs2: fix use-after-free bug of ns_writer on remount\n\nIf a nilfs2 filesystem is downgraded to read-only due to metadata\ncorruption on disk and is remounted read/write, or if emergency read-only\nremount is performed, detaching a log writer and synchronizing the\nfilesystem can be done at the same time.\n\nIn these cases, use-after-free of the log writer (hereinafter\nnilfs-\u003ens_writer) can happen as shown in the scenario below:\n\n Task1 Task2\n -------------------------------- ------------------------------\n nilfs_construct_segment\n nilfs_segctor_sync\n init_wait\n init_waitqueue_entry\n add_wait_queue\n schedule\n nilfs_remount (R/W remount case)\n\t\t\t\t nilfs_attach_log_writer\n nilfs_detach_log_writer\n nilfs_segctor_destroy\n kfree\n finish_wait\n _raw_spin_lock_irqsave\n __raw_spin_lock_irqsave\n do_raw_spin_lock\n debug_spin_lock_before \u003c-- use-after-free\n\nWhile Task1 is sleeping, nilfs-\u003ens_writer is freed by Task2. After Task1\nwaked up, Task1 accesses nilfs-\u003ens_writer which is already freed. This\nscenario diagram is based on the Shigeru Yoshida\u0027s post [1].\n\nThis patch fixes the issue by not detaching nilfs-\u003ens_writer on remount so\nthat this UAF race doesn\u0027t happen. Along with this change, this patch\nalso inserts a few necessary read-only checks with superblock instance\nwhere only the ns_writer pointer was used to check if the filesystem is\nread-only.",
"id": "GHSA-7jwj-6g7w-4c9q",
"modified": "2025-11-10T21:30:28Z",
"published": "2025-05-01T15:31:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-49834"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/39a3ed68270b079c6b874d4e4727a512b9b4882c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4feedde5486c07ea79787839153a71ca71329c7d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8cccf05fe857a18ee26e20d11a8455a73ffd4efd"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9b162e81045266a2d5b44df9dffdf05c54de9cca"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/afbd1188382a75f6cfe22c0b68533f7f9664f182"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b152300d5a1ba4258dacf9916bff20e6a8c7603b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b2fbf10040216ef5ee270773755fc2f5da65b749"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b4736ab5542112fe0a40f140a0a0b072954f34da"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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