GHSA-V8MR-FRX6-J364
Vulnerability from github – Published: 2025-05-20 18:30 – Updated: 2025-12-17 21:30In the Linux kernel, the following vulnerability has been resolved:
xenbus: Use kref to track req lifetime
Marek reported seeing a NULL pointer fault in the xenbus_thread callstack: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: e030:__wake_up_common+0x4c/0x180 Call Trace: __wake_up_common_lock+0x82/0xd0 process_msg+0x18e/0x2f0 xenbus_thread+0x165/0x1c0
process_msg+0x18e is req->cb(req). req->cb is set to xs_wake_up(), a thin wrapper around wake_up(), or xenbus_dev_queue_reply(). It seems like it was xs_wake_up() in this case.
It seems like req may have woken up the xs_wait_for_reply(), which kfree()ed the req. When xenbus_thread resumes, it faults on the zero-ed data.
Linux Device Drivers 2nd edition states: "Normally, a wake_up call can cause an immediate reschedule to happen, meaning that other processes might run before wake_up returns." ... which would match the behaviour observed.
Change to keeping two krefs on each request. One for the caller, and one for xenbus_thread. Each will kref_put() when finished, and the last will free it.
This use of kref matches the description in Documentation/core-api/kref.rst
{
"affected": [],
"aliases": [
"CVE-2025-37949"
],
"database_specific": {
"cwe_ids": [
"CWE-476"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-05-20T16:15:32Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nxenbus: Use kref to track req lifetime\n\nMarek reported seeing a NULL pointer fault in the xenbus_thread\ncallstack:\nBUG: kernel NULL pointer dereference, address: 0000000000000000\nRIP: e030:__wake_up_common+0x4c/0x180\nCall Trace:\n \u003cTASK\u003e\n __wake_up_common_lock+0x82/0xd0\n process_msg+0x18e/0x2f0\n xenbus_thread+0x165/0x1c0\n\nprocess_msg+0x18e is req-\u003ecb(req). req-\u003ecb is set to xs_wake_up(), a\nthin wrapper around wake_up(), or xenbus_dev_queue_reply(). It seems\nlike it was xs_wake_up() in this case.\n\nIt seems like req may have woken up the xs_wait_for_reply(), which\nkfree()ed the req. When xenbus_thread resumes, it faults on the zero-ed\ndata.\n\nLinux Device Drivers 2nd edition states:\n\"Normally, a wake_up call can cause an immediate reschedule to happen,\nmeaning that other processes might run before wake_up returns.\"\n... which would match the behaviour observed.\n\nChange to keeping two krefs on each request. One for the caller, and\none for xenbus_thread. Each will kref_put() when finished, and the last\nwill free it.\n\nThis use of kref matches the description in\nDocumentation/core-api/kref.rst",
"id": "GHSA-v8mr-frx6-j364",
"modified": "2025-12-17T21:30:29Z",
"published": "2025-05-20T18:30:56Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-37949"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0e94a246bb6d9538010b6c02d2b1d4717a97b2e5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1f0304dfd9d217c2f8b04a9ef4b3258a66eedd27"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2466b0f66795c3c426cacc8998499f38031dbb59"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4d260a5558df4650eb87bc41b2c9ac2d6b2ba447"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8b02f85e84dc6f7c150cef40ddb69af5a25659e5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8e9c8a0393b5f85f1820c565ab8105660f4e8f92"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cbfaf46b88a4c01b64c4186cdccd766c19ae644c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f1bcac367bc95631afbb918348f30dec887d0e1b"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2025/08/msg00010.html"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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