Re: [PATCH] mm/pagewalk.c: report holes in hugetlb ranges

[Greg KH <greg@kroah.com>]

On Wed, Nov 22, 2017 at 02:58:59PM +0100, Jann Horn wrote:
> commit 373c4557d2aa362702c4c2d41288fb1e54990b7c upstream.
> 
> This matters at least for the mincore syscall, which will otherwise copy
> uninitialized memory from the page allocator to userspace.  It is
> probably also a correctness error for /proc/$pid/pagemap, but I haven't
> tested that.
> 
> Removing the `walk->hugetlb_entry` condition in walk_hugetlb_range() has
> no effect because the caller already checks for that.
> 
> This only reports holes in hugetlb ranges to callers who have specified
> a hugetlb_entry callback.
> 
> This issue was found using an AFL-based fuzzer.
> 
> v2:
>  - don't crash on ->pte_hole==NULL (Andrew Morton)
>  - add Cc stable (Andrew Morton)
> 
> Changed for 4.4/4.9 stable backport:
>  - fix up conflict in the huge_pte_offset() call
> 
> Fixes: 1e25a271c8ac ("mincore: apply page table walker on do_mincore()")
> Signed-off-by: Jann Horn <jannh@google.com>
> ---
> Please apply this patch to <=4.9 stable trees instead of the
> original patch.

Thanks for the backport!

greg k-h