On Fri 21-07-17 14:18:31, Mike Kravetz wrote:
[...]
> >From 5c4a1602bd6a942544ed011dc0a72fd258e874b2 Mon Sep 17 00:00:00 2001
> From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Date: Wed, 12 Jul 2017 13:52:47 -0700
> Subject: [PATCH] mm/mremap: Fail map duplication attempts for private mappings
>
> mremap will attempt to create a 'duplicate' mapping if old_size
> == 0 is specified. In the case of private mappings, mremap
> will actually create a fresh separate private mapping unrelated
> to the original. This does not fit with the design semantics of
> mremap as the intention is to create a new mapping based on the
> original.
>
> Therefore, return EINVAL in the case where an attempt is made
> to duplicate a private mapping. Also, print a warning message
> (once) if such an attempt is made.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> mm/mremap.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index cd8a1b1..75b167d 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -383,6 +383,19 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> if (!vma || vma->vm_start > addr)
> return ERR_PTR(-EFAULT);
>
> + /*
> + * !old_len is a special case where an attempt is made to 'duplicate'
> + * a mapping. This makes no sense for private mappings as it will
> + * instead create a fresh/new mapping unrelated to the original. This
> + * is contrary to the basic idea of mremap which creates new mappings
> + * based on the original. There are no known use cases for this
> + * behavior. As a result, fail such attempts.
> + */
> + if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
> + pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap. This is not supported.\n", current->comm, current->pid);
> + return ERR_PTR(-EINVAL);
> + }
> +
> if (is_vm_hugetlb_page(vma))
> return ERR_PTR(-EINVAL);
>
> --
> 2.7.5
--
Michal Hocko
SUSE Labs
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