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Subject[PATCH 5.15 095/262] 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(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index cdfb1ae78a3f8..54c4e0b0dda4a 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


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