user_namespace: use kmemdup_array() instead of kmemdup() for multiple allocation

Let the kmemdup_array() take care about multiplication and possible
overflows.

Link: https://lkml.kernel.org/r/20240828072340.1249310-1-ruanjinjie@huawei.com


Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Li zeming <zeming@nfschina.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>