On Thu 03-01-19 20:27:26, Roman Penyaev wrote:
On 2019-01-03 16:13, Michal Hocko wrote:
On Thu 03-01-19 15:59:52, Roman Penyaev wrote:
area->size can include adjacent guard page but get_vm_area_size() returns actual size of the area.
This fixes possible kernel crash when userspace tries to map area on 1 page bigger: size check passes but the following vmalloc_to_page() returns NULL on last guard (non-existing) page.
Can this actually happen? I am not really familiar with all the callers of this API but VM_NO_GUARD is not really used wildly in the kernel.
Exactly, by default (VM_NO_GUARD is not set) each area has guard page, thus the area->size will be bigger. The bug is not reproduced if VM_NO_GUARD is set.
All I can see is kasan na arm64 which doesn't really seem to use it for vmalloc.
So is the problem real or this is a mere cleanup?
This is the real problem, try this hunk for any file descriptor which provides mapping, or say modify epoll as example:
OK, my response was more confusing than I intended. I meant to say. Is there any in kernel code that would allow the bug have had in mind? In other words can userspace trick any existing code?