[PATCH 5.15 134/159] ksmbd: fix race condition from parallel smb2 lock requests

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Namjae Jeon <linkinjeon@xxxxxxxxxx>

[ Upstream commit 75ac9a3dd65f7eab4d12b0a0f744234b5300a491 ]

There is a race condition issue between parallel smb2 lock request.

                                            Time
                                             +
Thread A                                     | Thread A
smb2_lock                                    | smb2_lock
                                             |
 insert smb_lock to lock_list                |
 spin_unlock(&work->conn->llist_lock)        |
                                             |
                                             |   spin_lock(&conn->llist_lock);
                                             |   kfree(cmp_lock);
                                             |
 // UAF!                                     |
 list_add(&smb_lock->llist, &rollback_list)  +

This patch swaps the line for adding the smb lock to the rollback list and
adding the lock list of connection to fix the race issue.

Reported-by: luosili <rootlab@xxxxxxxxxx>
Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/ksmbd/smb2pdu.c |   12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -7040,10 +7040,6 @@ skip:
 
 				ksmbd_debug(SMB,
 					    "would have to wait for getting lock\n");
-				spin_lock(&work->conn->llist_lock);
-				list_add_tail(&smb_lock->clist,
-					      &work->conn->lock_list);
-				spin_unlock(&work->conn->llist_lock);
 				list_add(&smb_lock->llist, &rollback_list);
 
 				argv = kmalloc(sizeof(void *), GFP_KERNEL);
@@ -7075,9 +7071,6 @@ skip:
 
 				if (work->state != KSMBD_WORK_ACTIVE) {
 					list_del(&smb_lock->llist);
-					spin_lock(&work->conn->llist_lock);
-					list_del(&smb_lock->clist);
-					spin_unlock(&work->conn->llist_lock);
 					locks_free_lock(flock);
 
 					if (work->state == KSMBD_WORK_CANCELLED) {
@@ -7097,19 +7090,16 @@ skip:
 				}
 
 				list_del(&smb_lock->llist);
-				spin_lock(&work->conn->llist_lock);
-				list_del(&smb_lock->clist);
-				spin_unlock(&work->conn->llist_lock);
 				release_async_work(work);
 				goto retry;
 			} else if (!rc) {
+				list_add(&smb_lock->llist, &rollback_list);
 				spin_lock(&work->conn->llist_lock);
 				list_add_tail(&smb_lock->clist,
 					      &work->conn->lock_list);
 				list_add_tail(&smb_lock->flist,
 					      &fp->lock_list);
 				spin_unlock(&work->conn->llist_lock);
-				list_add(&smb_lock->llist, &rollback_list);
 				ksmbd_debug(SMB, "successful in taking lock\n");
 			} else {
 				goto out;