GHSA-H7C8-WRGV-C7F2
Vulnerability from github – Published: 2026-07-19 12:30 – Updated: 2026-07-29 21:30In the Linux kernel, the following vulnerability has been resolved:
gfs2: fix use-after-free in gfs2_qd_dealloc
gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(), accesses the superblock object sdp through qd->qd_sbd after freeing qd. It does so to decrement sd_quota_count and wake up sd_kill_wait.
However, by the time the RCU callback runs, gfs2_put_super() may have already freed sdp via free_sbd(). This can happen when gfs2_quota_cleanup() is called during unmount: it disposes of quota objects via call_rcu() and then waits on sd_kill_wait with a 60-second timeout. If the timeout expires, or if gfs2_gl_hash_clear() triggers additional qd_put() calls that schedule more RCU callbacks after the wait completes, gfs2_put_super() will proceed to free the superblock while RCU callbacks referencing it are still pending.
Add an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure all pending RCU callbacks (including gfs2_qd_dealloc) have completed before the superblock is freed.
{
"affected": [],
"aliases": [
"CVE-2026-63804"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-19T12:16:53Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ngfs2: fix use-after-free in gfs2_qd_dealloc\n\ngfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(),\naccesses the superblock object sdp through qd-\u003eqd_sbd after freeing qd.\nIt does so to decrement sd_quota_count and wake up sd_kill_wait.\n\nHowever, by the time the RCU callback runs, gfs2_put_super() may have\nalready freed sdp via free_sbd(). This can happen when\ngfs2_quota_cleanup() is called during unmount: it disposes of quota\nobjects via call_rcu() and then waits on sd_kill_wait with a 60-second\ntimeout. If the timeout expires, or if gfs2_gl_hash_clear() triggers\nadditional qd_put() calls that schedule more RCU callbacks after the\nwait completes, gfs2_put_super() will proceed to free the superblock\nwhile RCU callbacks referencing it are still pending.\n\nAdd an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure\nall pending RCU callbacks (including gfs2_qd_dealloc) have completed\nbefore the superblock is freed.",
"id": "GHSA-h7c8-wrgv-c7f2",
"modified": "2026-07-29T21:30:54Z",
"published": "2026-07-19T12:30:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63804"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4fe388218826df8607ae41a6305df67db08a9093"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8745d9f7e1682c39f0a1578895ac74205e2a6757"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f9c9ec2c319f843b70ecdf939d48b52d189bc081"
}
],
"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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