+ hugetlbfs-fix-off-by-one-error-in-hugetlb_vmdelete_list.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: hugetlbfs: fix off-by-one error in hugetlb_vmdelete_list()
has been added to the -mm tree.  Its filename is
     hugetlbfs-fix-off-by-one-error-in-hugetlb_vmdelete_list.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/hugetlbfs-fix-off-by-one-error-in-hugetlb_vmdelete_list.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/hugetlbfs-fix-off-by-one-error-in-hugetlb_vmdelete_list.patch

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------------------------------------------------------
From: Sean Christopherson <seanjc@google.com>
Subject: hugetlbfs: fix off-by-one error in hugetlb_vmdelete_list()

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>
---

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

--- a/fs/hugetlbfs/inode.c~hugetlbfs-fix-off-by-one-error-in-hugetlb_vmdelete_list
+++ a/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;
 
_

Patches currently in -mm which might be from seanjc@google.com are

hugetlbfs-fix-off-by-one-error-in-hugetlb_vmdelete_list.patch