CVE-2025-40090

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.