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    Subject[PATCH 5.16 0833/1039] hugetlbfs: fix off-by-one error in hugetlb_vmdelete_list()
    Date
    From: Sean Christopherson <seanjc@google.com>

    [ Upstream commit d6aba4c8e20d4d2bf65d589953f6d891c178f3a3 ]

    Pass "end - 1" instead of "end" when walking the interval tree in
    hugetlb_vmdelete_list() to fix an inclusive vs. exclusive bug. The two
    callers that pass a non-zero "end" treat it as exclusive, whereas the
    interval tree iterator expects an inclusive "last". E.g. punching a
    hole in a file that precisely matches the size of a single hugepage,
    with a vma starting right on the boundary, will result in
    unmap_hugepage_range() being called twice, with the second call having
    start==end.

    The off-by-one error doesn't cause functional problems as
    __unmap_hugepage_range() turns into a massive nop due to
    short-circuiting its for-loop on "address < end". But, the mmu_notifier
    invocations to invalid_range_{start,end}() are passed a bogus zero-sized
    range, which may be unexpected behavior for secondary MMUs.

    The bug was exposed by commit ed922739c919 ("KVM: Use interval tree to
    do fast hva lookup in memslots"), currently queued in the KVM tree for
    5.17, which added a WARN to detect ranges with start==end.

    Link: https://lkml.kernel.org/r/20211228234257.1926057-1-seanjc@google.com
    Fixes: 1bfad99ab425 ("hugetlbfs: hugetlb_vmtruncate_list() needs to take a range to delete")
    Signed-off-by: Sean Christopherson <seanjc@google.com>
    Reported-by: syzbot+4e697fe80a31aa7efe21@syzkaller.appspotmail.com
    Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/hugetlbfs/inode.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/fs/hugetlbfs/inode.c
    +++ b/fs/hugetlbfs/inode.c
    @@ -409,10 +409,11 @@ hugetlb_vmdelete_list(struct rb_root_cac
    struct vm_area_struct *vma;

    /*
    - * end == 0 indicates that the entire range after
    - * start should be unmapped.
    + * end == 0 indicates that the entire range after start should be
    + * unmapped. Note, end is exclusive, whereas the interval tree takes
    + * an inclusive "last".
    */
    - vma_interval_tree_foreach(vma, root, start, end ? end : ULONG_MAX) {
    + vma_interval_tree_foreach(vma, root, start, end ? end - 1 : ULONG_MAX) {
    unsigned long v_offset;
    unsigned long v_end;


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