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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
