CVE-2025-37949: xenbus: Use kref to track req lifetime

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-05-20 · updated 2026-10-15
Weakness: CWE-476

Description

In 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: <TASK> __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 products

Debian Linux: 11.0
Linux kernel: from 4.11 before 5.4.294; from 5.5 before 5.10.238; from 5.11 before 5.15.183; from 5.16 before 6.1.139; from 6.2 before 6.6.91; from 6.7 before 6.12.29 — fixed in 5.10.238, 5.15.183, 5.4.294, 6.1.139, 6.12.29, 6.14.7

How to fix

Upgrade to a fixed version: Linux kernel 5.10.238, 5.15.183, 5.4.294, 6.1.139. Check the vendor advisory for mitigations.

References

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