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    SubjectRe: [RFC] invalidate_mmap_range() misses remap_file_pages()-affected targets
    William Lee Irwin III <wli@holomorphy.com> wrote:
    >
    > invalidate_mmap_range(), and hence vmtruncate(), can miss its targets
    > due to remap_file_pages() disturbing the former invariant of file
    > offsets only being mapped within vmas tagged as mapping file offset
    > ranges containing them.

    I was going to just not bother about this wart. After all, we get to write
    the standard on remap_file_pages(), and we can say "the
    truncate-causes-SIGBUS thing doesn't work". After all, it is not very
    useful.

    But I wonder if this effect could be used maliciously. Say, user A has
    read-only access to user B's file, and uses that access to set up a
    nonlinear mapping thereby causing user B's truncate to not behave
    correctly. But this example is OK, isn't it? User A will just receive an
    anonymous page for his troubles.

    Can you think of any stability or security scenario which says that we
    _should_ implement the conventional truncate behaviour?

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