linux-kernel - [PATCH 5.16 0833/1039] hugetlbfs: fix off-by-one error in hugetlb_vmdelete

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Message-Id: <20220124184153.284397402@linuxfoundation.org>
Date:   Mon, 24 Jan 2022 19:43:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        syzbot+4e697fe80a31aa7efe21@...kaller.appspotmail.com,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 0833/1039] hugetlbfs: fix off-by-one error in hugetlb_vmdelete_list()

From: Sean Christopherson <seanjc@...gle.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@...gle.com>
Reported-by: syzbot+4e697fe80a31aa7efe21@...kaller.appspotmail.com
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.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;