CVE-2025-37949 Information
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:
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.\n… 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
Reference
https://git.kernel.org/stable/c/1f0304dfd9d217c2f8b04a9ef4b3258a66eedd27 https://git.kernel.org/stable/c/2466b0f66795c3c426cacc8998499f38031dbb59 https://git.kernel.org/stable/c/4d260a5558df4650eb87bc41b2c9ac2d6b2ba447 https://git.kernel.org/stable/c/8b02f85e84dc6f7c150cef40ddb69af5a25659e5 https://git.kernel.org/stable/c/8e9c8a0393b5f85f1820c565ab8105660f4e8f92 https://git.kernel.org/stable/c/cbfaf46b88a4c01b64c4186cdccd766c19ae644c
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