linux-cve-announce - CVE-2025-40090: ksmbd: fix recursive locking in RPC handle list access

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Message-ID: <2025103015-CVE-2025-40090-d560@gregkh>
Date: Thu, 30 Oct 2025 10:48:17 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40090: ksmbd: fix recursive locking in RPC handle list access

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix recursive locking in RPC handle list access

Since commit 305853cce3794 ("ksmbd: Fix race condition in RPC handle list
access"), ksmbd_session_rpc_method() attempts to lock sess->rpc_lock.

This causes hung connections / tasks when a client attempts to open
a named pipe. Using Samba's rpcclient tool:

 $ rpcclient //192.168.1.254 -U user%password
 $ rpcclient $> srvinfo
 <connection hung here>

Kernel side:
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  task:kworker/0:0 state:D stack:0 pid:5021 tgid:5021 ppid:2 flags:0x00200000
  Workqueue: ksmbd-io handle_ksmbd_work
  Call trace:
  __schedule from schedule+0x3c/0x58
  schedule from schedule_preempt_disabled+0xc/0x10
  schedule_preempt_disabled from rwsem_down_read_slowpath+0x1b0/0x1d8
  rwsem_down_read_slowpath from down_read+0x28/0x30
  down_read from ksmbd_session_rpc_method+0x18/0x3c
  ksmbd_session_rpc_method from ksmbd_rpc_open+0x34/0x68
  ksmbd_rpc_open from ksmbd_session_rpc_open+0x194/0x228
  ksmbd_session_rpc_open from create_smb2_pipe+0x8c/0x2c8
  create_smb2_pipe from smb2_open+0x10c/0x27ac
  smb2_open from handle_ksmbd_work+0x238/0x3dc
  handle_ksmbd_work from process_scheduled_works+0x160/0x25c
  process_scheduled_works from worker_thread+0x16c/0x1e8
  worker_thread from kthread+0xa8/0xb8
  kthread from ret_from_fork+0x14/0x38
  Exception stack(0x8529ffb0 to 0x8529fff8)

The task deadlocks because the lock is already held:
  ksmbd_session_rpc_open
    down_write(&sess->rpc_lock)
    ksmbd_rpc_open
      ksmbd_session_rpc_method
        down_read(&sess->rpc_lock)   <-- deadlock

Adjust ksmbd_session_rpc_method() callers to take the lock when necessary.

The Linux kernel CVE team has assigned CVE-2025-40090 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.12.53 with commit 5cc679ba0f4505936124cd4179ba66bb0a4bd9f3 and fixed in 6.12.55 with commit 4602b8cee1481dbb896182e5cb1e8cf12910e9e7
	Issue introduced in 6.17.3 with commit 6bd7e0e55dcea2cf0d391bbc21c2eb069b4be3e1 and fixed in 6.17.5 with commit 3412fbd81b46b9cfae013817b61d4bbd27e09e36
	Issue introduced in 6.18-rc1 with commit 305853cce379407090a73b38c5de5ba748893aee and fixed in 6.18-rc2 with commit 88f170814fea74911ceab798a43cbd7c5599bed4

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-2025-40090
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:
	fs/smb/server/mgmt/user_session.c
	fs/smb/server/smb2pdu.c
	fs/smb/server/transport_ipc.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/4602b8cee1481dbb896182e5cb1e8cf12910e9e7
	https://git.kernel.org/stable/c/3412fbd81b46b9cfae013817b61d4bbd27e09e36
	https://git.kernel.org/stable/c/88f170814fea74911ceab798a43cbd7c5599bed4