FROMLIST: binder: check offset alignment in binder_get_object()

Commit 6d98eb95b450 ("binder: avoid potential data leakage when copying
txn") introduced changes to how binder objects are copied. In doing so,
it unintentionally removed an offset alignment check done through calls
to binder_alloc_copy_from_buffer() -> check_buffer().

These calls were replaced in binder_get_object() with copy_from_user(),
so now an explicit offset alignment check is needed here. This avoids
later complications when unwinding the objects gets harder.

It is worth noting this check existed prior to commit 7a67a393
("binder: add function to copy binder object from buffer"), likely
removed due to redundancy at the time.

Fixes: 6d98eb95b450 ("binder: avoid potential data leakage when copying txn")
Cc:  <stable@vger.kernel.org>
Acked-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>

Bug: 320661088
Link: https://lore.kernel.org/all/20240330190115.1877819-1-cmllamas@google.com/


Change-Id: Iaddabaa28de7ba7b7d35dbb639d38ca79dbc5077
Signed-off-by: Carlos Llamas <cmllamas@google.com>