ksmbd: fix memory leaks and NULL deref in smb2_lock()

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

ksmbd: fix memory leaks and NULL deref in smb2_lock()

smb2_lock() has three error handling issues after list_del() detaches

smb_lock from lock_list at no_check_cl:

1) If vfs_lock_file() returns an unexpected error in the non-UNLOCK

path, goto out leaks smb_lock and its flock because the out:

handler only iterates lock_list and rollback_list, neither of

which contains the detached smb_lock.

2) If vfs_lock_file() returns -ENOENT in the UNLOCK path, goto out

leaks smb_lock and flock for the same reason. The error code

returned to the dispatcher is also stale.

3) In the rollback path, smb_flock_init() can return NULL on

allocation failure. The result is dereferenced unconditionally,

causing a kernel NULL pointer dereference. Add a NULL check to

prevent the crash and clean up the bookkeeping; the VFS lock

itself cannot be rolled back without the allocation and will be

released at file or connection teardown.

Fix cases 1 and 2 by hoisting the locks_free_lock()/kfree() to before

the if(!rc) check in the UNLOCK branch so all exit paths share one

free site, and by freeing smb_lock and flock before goto out in the

non-UNLOCK branch. Propagate the correct error code in both cases.

Fix case 3 by wrapping the VFS unlock in an if(rlock) guard and adding

a NULL check for locks_free_lock(rlock) in the shared cleanup.

Found via call-graph analysis using sqry.