Hi Mathieu,

On (10/16/18 15:17), Mathieu Desnoyers wrote:

Therefore, only an internal kernel bug between vm_map_user_ram() and
vm_unmap_user_ram() should trigger the BUG_ON(). No user input is passed
to vm_unmap_user_ram().

Now, let's look at vm_map_user_ram(). It calls alloc_vmap_area(), which returns
a vmap_area. Then if vmap_page_range failed, vm_unmap_user_ram is called on the
memory that has just been returned by vm_map_user_ram. Again, only an internal
bug between map/unmap can trigger the BUG_ON() in vm_unmap_user_ram.

Thanks for spending time on this.
Just wanted someone to have extra look at syscall->BUG_ON().

	-ss