Commit dba58d3b authored Sep 06, 2017 by Mike Kravetz Committed by Linus Torvalds Sep 06, 2017

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.

Link: http://lkml.kernel.org/r/cb9d9f6a-7095-582f-15a5-62643d65c736@oracle.com


Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 10903027

mm/mremap.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -384,6 +384,19 @@ 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);

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