The patch titled
Subject: mm/mremap: fail map duplication attempts for private mappings
has been added to the -mm tree. Its filename is
mm-mremap-fail-map-duplication-attempts-for-private-mappings.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-mremap-fail-map-duplication-attempts-for-private-mappings.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-mremap-fail-map-duplication-attempts-for-private-mappings.patch
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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Aaron Lu <aaron.lu@xxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mremap.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff -puN mm/mremap.c~mm-mremap-fail-map-duplication-attempts-for-private-mappings mm/mremap.c
--- a/mm/mremap.c~mm-mremap-fail-map-duplication-attempts-for-private-mappings
+++ a/mm/mremap.c
@@ -384,6 +384,19 @@ static struct vm_area_struct *vma_to_res
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);
_
Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
mm-mremap-fail-map-duplication-attempts-for-private-mappings.patch
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