GHSA-29WC-2986-775F
Vulnerability from github – Published: 2026-09-16 09:30 – Updated: 2026-10-30 15:33In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix tree connection use-after-free in smb2_tree_connect()
ksmbd_tree_conn_connect() publishes a new tree connection in sess->tree_conns with a single reference and returns its pointer to smb2_tree_connect(). The handler continues to initialize the object and build the response after publication. A concurrent session logoff can erase the connection and drop that reference, freeing the object while the handler still uses it.
BUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90 smb2_tree_connect (fs/smb/server/smb2pdu.c:2872) handle_ksmbd_work process_one_work worker_thread kthread
After xa_store() succeeds, take a second reference before releasing tree_conns_lock. The original reference belongs to the xarray entry and the second belongs to the creating smb2_tree_connect() handler.
Keep the references balanced in every path:
- On normal exit or an error after publication, smb2_tree_connect() drops its creator reference. Error cleanup also calls ksmbd_tree_conn_disconnect(), which drops the xarray reference only if it removes the exact entry.
- SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop its xarray reference. The request's existing lookup reference remains owned by the request and is released by the existing cleanup.
- Session LOGOFF removes each entry and drops its xarray reference. If it wins the race, later cleanup sees that the entry is gone and does not drop that reference again.
To enforce this ownership, claim the disconnected state and erase the exact entry atomically under tree_conns_lock. This guarantees one drop for the xarray reference and one drop by each in-flight user, regardless of which teardown path wins. If logoff removes the entry before initialization completes, fail the connect instead of marking the detached object TREE_CONNECTED.
{
"affected": [],
"aliases": [
"CVE-2026-89788"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T09:17:09Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix tree connection use-after-free in smb2_tree_connect()\n\nksmbd_tree_conn_connect() publishes a new tree connection in\nsess-\u003etree_conns with a single reference and returns its pointer to\nsmb2_tree_connect(). The handler continues to initialize the object and\nbuild the response after publication. A concurrent session logoff can\nerase the connection and drop that reference, freeing the object while\nthe handler still uses it.\n\nBUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90\n smb2_tree_connect (fs/smb/server/smb2pdu.c:2872)\n handle_ksmbd_work\n process_one_work\n worker_thread\n kthread\n\nAfter xa_store() succeeds, take a second reference before releasing\ntree_conns_lock. The original reference belongs to the xarray entry and\nthe second belongs to the creating smb2_tree_connect() handler.\n\nKeep the references balanced in every path:\n\n- On normal exit or an error after publication, smb2_tree_connect()\n drops its creator reference. Error cleanup also calls\n ksmbd_tree_conn_disconnect(), which drops the xarray reference only if\n it removes the exact entry.\n- SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop\n its xarray reference. The request\u0027s existing lookup reference remains\n owned by the request and is released by the existing cleanup.\n- Session LOGOFF removes each entry and drops its xarray reference. If\n it wins the race, later cleanup sees that the entry is gone and does\n not drop that reference again.\n\nTo enforce this ownership, claim the disconnected state and erase the\nexact entry atomically under tree_conns_lock. This guarantees one drop\nfor the xarray reference and one drop by each in-flight user, regardless\nof which teardown path wins. If logoff removes the entry before\ninitialization completes, fail the connect instead of marking the\ndetached object TREE_CONNECTED.",
"id": "GHSA-29wc-2986-775f",
"modified": "2026-10-30T15:33:27Z",
"published": "2026-09-16T09:30:30Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89788"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4e30fbd26e84efa2e5cbec4eb11e126ac0c79313"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/63f5939b50470ef4d245c16d2098376b952beb51"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b5ec6c462aab1062cf5d1e667ba7c6442f737055"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bd58a52738f7576ee5f5eb74243df13f902c8051"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ca3a3984bf445aaec69f6937f11e560d4b849365"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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