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    Subject[01/70] vm: fix vm_pgoff wrap in stack expansion
    2.6.38-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Linus Torvalds <torvalds@linux-foundation.org>

    commit a626ca6a656450e9f4df91d0dda238fff23285f4 upstream.

    Commit 982134ba6261 ("mm: avoid wrapping vm_pgoff in mremap()") fixed
    the case of a expanding mapping causing vm_pgoff wrapping when you used
    mremap. But there was another case where we expand mappings hiding in
    plain sight: the automatic stack expansion.

    This fixes that case too.

    This one also found by Robert Święcki, using his nasty system call
    fuzzer tool. Good job.

    Reported-and-tested-by: Robert Święcki <robert@swiecki.net>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    mm/mmap.c | 13 ++++++++-----
    1 file changed, 8 insertions(+), 5 deletions(-)

    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -1814,11 +1814,14 @@ static int expand_downwards(struct vm_ar
    size = vma->vm_end - address;
    grow = (vma->vm_start - address) >> PAGE_SHIFT;

    - error = acct_stack_growth(vma, size, grow);
    - if (!error) {
    - vma->vm_start = address;
    - vma->vm_pgoff -= grow;
    - perf_event_mmap(vma);
    + error = -ENOMEM;
    + if (grow <= vma->vm_pgoff) {
    + error = acct_stack_growth(vma, size, grow);
    + if (!error) {
    + vma->vm_start = address;
    + vma->vm_pgoff -= grow;
    + perf_event_mmap(vma);
    + }
    }
    }
    vma_unlock_anon_vma(vma);

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