ksmbd: fix UAF of struct file_lock in SMB2_LOCK deferred-lock cancellation

When a blocking byte-range lock request is deferred in the
FILE_LOCK_DEFERRED path, ksmbd registers the asynchronous work into
the connection's async_requests list via setup_async_work(). The cancel
callback smb2_remove_blocked_lock() holds a reference to the flock.

If the lock waiter is subsequently woken up but the work state is no
longer KSMBD_WORK_ACTIVE (e.g., due to a concurrent cancellation), the
cleanup path calls locks_free_lock(flock) without dequeuing the work from
the async_requests list. Concurrently, smb2_cancel() walks the list
under conn->request_lock and invokes the cancel callback, which then
dereferences the already freed 'flock'. This leads to a slab-use-after-free
inside __wake_up_common.

Fix this by restructuring the cleanup logic after the worker returns
from ksmbd_vfs_posix_lock_wait(). Move list_del(&smb_lock->llist) and
release_async_work(work) to the top of the cleanup block. This guarantees
that the async work is completely dequeued and serialized under
conn->request_lock before locks_free_lock(flock) is called, rendering
the flock unreachable for any concurrent smb2_cancel().

Cc: stable@vger.kernel.org
Signed-off-by: Davide Ornaghi <d.ornaghi97@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 16 insertions, 18 deletions

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 00e63debcbe9..82f93b191c6c 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -7755,29 +7755,27 @@ skip:
 				list_del(&work->fp_entry);
 				spin_unlock(&fp->f_lock);
 
-				if (work->state != KSMBD_WORK_ACTIVE) {
-					list_del(&smb_lock->llist);
-					locks_free_lock(flock);
+				list_del(&smb_lock->llist);
+				release_async_work(work);
 
-					if (work->state == KSMBD_WORK_CANCELLED) {
-						rsp->hdr.Status =
-							STATUS_CANCELLED;
-						kfree(smb_lock);
-						smb2_send_interim_resp(work,
-								       STATUS_CANCELLED);
-						work->send_no_response = 1;
-						goto out;
-					}
+				if (work->state == KSMBD_WORK_ACTIVE)
+					goto retry;
+
+				locks_free_lock(flock);
 
-					rsp->hdr.Status =
-						STATUS_RANGE_NOT_LOCKED;
+				if (work->state == KSMBD_WORK_CANCELLED) {
+					rsp->hdr.Status = STATUS_CANCELLED;
 					kfree(smb_lock);
-					goto out2;
+					smb2_send_interim_resp(work,
+							STATUS_CANCELLED);
+					work->send_no_response = 1;
+					goto out;
 				}
 
-				list_del(&smb_lock->llist);
-				release_async_work(work);
-				goto retry;
+				rsp->hdr.Status =
+					STATUS_RANGE_NOT_LOCKED;
+				kfree(smb_lock);
+				goto out2;
 			} else if (!rc) {
 				list_add(&smb_lock->llist, &rollback_list);
 				spin_lock(&work->conn->llist_lock);