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
Metrics
Affected Vendors & Products
| Source | ID | Title |
|---|---|---|
Debian DLA |
DLA-4271-1 | linux-6.1 security update |
Debian DLA |
DLA-4327-1 | linux security update |
Debian DSA |
DSA-5925-1 | linux security update |
EUVD |
EUVD-2025-15894 | 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 |
Ubuntu USN |
USN-7654-1 | Linux kernel vulnerabilities |
Ubuntu USN |
USN-7654-2 | Linux kernel (Real-time) vulnerabilities |
Ubuntu USN |
USN-7654-3 | Linux kernel (FIPS) vulnerabilities |
Ubuntu USN |
USN-7654-4 | Linux kernel (KVM) vulnerabilities |
Ubuntu USN |
USN-7654-5 | Linux kernel (Xilinx ZynqMP) vulnerabilities |
Ubuntu USN |
USN-7655-1 | Linux kernel (Intel IoTG) vulnerabilities |
Ubuntu USN |
USN-7686-1 | Linux kernel (Raspberry Pi) vulnerabilities |
Ubuntu USN |
USN-7699-1 | Linux kernel vulnerabilities |
Ubuntu USN |
USN-7699-2 | Linux kernel (HWE) vulnerabilities |
Ubuntu USN |
USN-7711-1 | Linux kernel (Azure) vulnerabilities |
Ubuntu USN |
USN-7712-1 | Linux kernel (Azure FIPS) vulnerabilities |
Ubuntu USN |
USN-7712-2 | Linux kernel (Azure) vulnerabilities |
Ubuntu USN |
USN-7721-1 | Linux kernel (Azure) vulnerabilities |
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
Wed, 17 Dec 2025 20:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Debian
Debian debian Linux |
|
| Weaknesses | CWE-476 | |
| CPEs | cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.15:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.15:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.15:rc3:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.15:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.15:rc5:*:*:*:*:*:* |
|
| Vendors & Products |
Debian
Debian debian Linux |
|
| Metrics |
cvssV3_1
|
cvssV3_1
|
Mon, 03 Nov 2025 20:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
Mon, 03 Nov 2025 18:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
Mon, 14 Jul 2025 13:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
epss
|
epss
|
Fri, 13 Jun 2025 19:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
cvssV3_1
|
cvssV3_1
|
Wed, 04 Jun 2025 13:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
Thu, 22 May 2025 02:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Tue, 20 May 2025 16:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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 | |
| Title | xenbus: Use kref to track req lifetime | |
| References |
|
|
Projects
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Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2025-11-03T19:57:40.135Z
Reserved: 2025-04-16T04:51:23.972Z
Link: CVE-2025-37949
No data.
Status : Analyzed
Published: 2025-05-20T16:15:32.920
Modified: 2025-12-17T20:05:13.020
Link: CVE-2025-37949
OpenCVE Enrichment
Updated: 2025-06-27T09:26:50Z
Debian DLA
Debian DSA
EUVD
Ubuntu USN