[PATCH 6.6 67/72] ksmbd: fix recursive locking in RPC handle list access

Greg Kroah-Hartman
2026-02-04T15:22:43Z

From: Marios Makassikis <mmakassikis@freebox.fr>

[ Upstream commit 88f170814fea74911ceab798a43cbd7c5599bed4 ]

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.

Fixes: 305853cce3794 ("ksmbd: Fix race condition in RPC handle list access")
Signed-off-by: Marios Makassikis <mmakassikis@freebox.fr>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Li hongliang <1468888505@139.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/server/mgmt/user_session.c | 7 ++-----
fs/smb/server/smb2pdu.c | 9 ++++++++-
fs/smb/server/transport_ipc.c | 12 ++++++++++++
3 files changed, 22 insertions(+), 6 deletions(-)

--- a/fs/smb/server/mgmt/user_session.c
+++ b/fs/smb/server/mgmt/user_session.c
@@ -147,14 +147,11 @@ void ksmbd_session_rpc_close(struct ksmb
int ksmbd_session_rpc_method(struct ksmbd_session *sess, int id)
{
struct ksmbd_session_rpc *entry;
- int method;

- down_read(&sess->rpc_lock);
+ lockdep_assert_held(&sess->rpc_lock);
entry = xa_load(&sess->rpc_handle_list, id);
- method = entry ? entry->method : 0;
- up_read(&sess->rpc_lock);

- return method;
+ return entry ? entry->method : 0;
}

void ksmbd_session_destroy(struct ksmbd_session *sess)
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -4614,8 +4614,15 @@ static int smb2_get_info_file_pipe(struc
* pipe without opening it, checking error condition here
*/
id = req->VolatileFileId;
- if (!ksmbd_session_rpc_method(sess, id))
+
+ lockdep_assert_not_held(&sess->rpc_lock);
+
+ down_read(&sess->rpc_lock);
+ if (!ksmbd_session_rpc_method(sess, id)) {
+ up_read(&sess->rpc_lock);
return -ENOENT;
+ }
+ up_read(&sess->rpc_lock);

ksmbd_debug(SMB, "FileInfoClass %u, FileId 0x%llx\n",
req->FileInfoClass, req->VolatileFileId);
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -778,6 +778,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_writ
if (!msg)
return NULL;

+ lockdep_assert_not_held(&sess->rpc_lock);
+
+ down_read(&sess->rpc_lock);
msg->type = KSMBD_EVENT_RPC_REQUEST;
req = (struct ksmbd_rpc_command *)msg->payload;
req->handle = handle;
@@ -786,6 +789,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_writ
req->flags |= KSMBD_RPC_WRITE_METHOD;
req->payload_sz = payload_sz;
memcpy(req->payload, payload, payload_sz);
+ up_read(&sess->rpc_lock);

resp = ipc_msg_send_request(msg, req->handle);
ipc_msg_free(msg);
@@ -802,6 +806,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_read
if (!msg)
return NULL;

+ lockdep_assert_not_held(&sess->rpc_lock);
+
+ down_read(&sess->rpc_lock);
msg->type = KSMBD_EVENT_RPC_REQUEST;
req = (struct ksmbd_rpc_command *)msg->payload;
req->handle = handle;
@@ -809,6 +816,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_read
req->flags |= rpc_context_flags(sess);
req->flags |= KSMBD_RPC_READ_METHOD;
req->payload_sz = 0;
+ up_read(&sess->rpc_lock);

resp = ipc_msg_send_request(msg, req->handle);
ipc_msg_free(msg);
@@ -829,6 +837,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioct
if (!msg)
return NULL;

+ lockdep_assert_not_held(&sess->rpc_lock);
+
+ down_read(&sess->rpc_lock);
msg->type = KSMBD_EVENT_RPC_REQUEST;
req = (struct ksmbd_rpc_command *)msg->payload;
req->handle = handle;
@@ -837,6 +848,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioct
req->flags |= KSMBD_RPC_IOCTL_METHOD;
req->payload_sz = payload_sz;
memcpy(req->payload, payload, payload_sz);
+ up_read(&sess->rpc_lock);

resp = ipc_msg_send_request(msg, req->handle);
ipc_msg_free(msg);