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Subject[PATCH] hugetlbfs: Fix off-by-one error in hugetlb_vmdelete_list()
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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.

Reported-by: syzbot+4e697fe80a31aa7efe21@syzkaller.appspotmail.com
Fixes: 1bfad99ab425 ("hugetlbfs: hugetlb_vmtruncate_list() needs to take a range to delete")
Cc: kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---

Not sure if this should go to stable@. It's mostly harmless, and likely
nothing more than a minor performance blip when it's not harmless.

fs/hugetlbfs/inode.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 49d2e686be74..a7c6c7498be0 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -409,10 +409,11 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end)
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;

--
2.34.1.448.ga2b2bfdf31-goog
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