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.
> 
> Signed-off-by: Roman Penyaev <rpeny...@suse.de>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Michal Hocko <mho...@suse.com>
> Cc: Andrey Ryabinin <aryabi...@virtuozzo.com>
> Cc: Joe Perches <j...@perches.com>
> Cc: "Luis R. Rodriguez" <mcg...@kernel.org>
> Cc: linux...@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: sta...@vger.kernel.org

Forgot to add
Acked-by: Michal Hocko <mho...@suse.com>
Although I am not really sure the stable backport is really needed as I
haven't seen any explicit example of a buggy kernel code to trigger the
issue.

> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 871e41c55e23..2cd24186ba84 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2248,7 +2248,7 @@ int remap_vmalloc_range_partial(struct vm_area_struct 
> *vma, unsigned long uaddr,
>       if (!(area->flags & VM_USERMAP))
>               return -EINVAL;
>  
> -     if (kaddr + size > area->addr + area->size)
> +     if (kaddr + size > area->addr + get_vm_area_size(area))
>               return -EINVAL;
>  
>       do {
> -- 
> 2.19.1

-- 
Michal Hocko
SUSE Labs

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