| From bippy-1.2.0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@kernel.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2025-37949: xenbus: Use kref to track req lifetime |
| |
| 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 |
| |
| The Linux kernel CVE team has assigned CVE-2025-37949 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 5.4.294 with commit 0e94a246bb6d9538010b6c02d2b1d4717a97b2e5 |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 5.10.238 with commit f1bcac367bc95631afbb918348f30dec887d0e1b |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 5.15.183 with commit 4d260a5558df4650eb87bc41b2c9ac2d6b2ba447 |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 6.1.139 with commit 8b02f85e84dc6f7c150cef40ddb69af5a25659e5 |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 6.6.91 with commit cbfaf46b88a4c01b64c4186cdccd766c19ae644c |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 6.12.29 with commit 8e9c8a0393b5f85f1820c565ab8105660f4e8f92 |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 6.14.7 with commit 2466b0f66795c3c426cacc8998499f38031dbb59 |
| Issue introduced in 4.11 with commit fd8aa9095a95c02dcc35540a263267c29b8fda9d and fixed in 6.15 with commit 1f0304dfd9d217c2f8b04a9ef4b3258a66eedd27 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2025-37949 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| drivers/xen/xenbus/xenbus.h |
| drivers/xen/xenbus/xenbus_comms.c |
| drivers/xen/xenbus/xenbus_dev_frontend.c |
| drivers/xen/xenbus/xenbus_xs.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/0e94a246bb6d9538010b6c02d2b1d4717a97b2e5 |
| https://git.kernel.org/stable/c/f1bcac367bc95631afbb918348f30dec887d0e1b |
| https://git.kernel.org/stable/c/4d260a5558df4650eb87bc41b2c9ac2d6b2ba447 |
| https://git.kernel.org/stable/c/8b02f85e84dc6f7c150cef40ddb69af5a25659e5 |
| https://git.kernel.org/stable/c/cbfaf46b88a4c01b64c4186cdccd766c19ae644c |
| https://git.kernel.org/stable/c/8e9c8a0393b5f85f1820c565ab8105660f4e8f92 |
| https://git.kernel.org/stable/c/2466b0f66795c3c426cacc8998499f38031dbb59 |
| https://git.kernel.org/stable/c/1f0304dfd9d217c2f8b04a9ef4b3258a66eedd27 |
