| Message ID | 20211228234257.1926057-1-seanjc@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | hugetlbfs: Fix off-by-one error in hugetlb_vmdelete_list() | expand |
+Cc Andrew if he wants to take it though his tree. On 12/28/21 15:42, Sean Christopherson wrote: > 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> Thanks Sean! Reviewed-by: Mike Kravetz <mike.kravetz@oracle.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. I am also unsure about the need to send to stable. It is possible automation will pick it up and make that decision for us.
On Tue, 28 Dec 2021 19:52:37 -0800 Mike Kravetz <mike.kravetz@oracle.com> wrote: > +Cc Andrew if he wants to take it though his tree. Sure. > > > > 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. > > I am also unsure about the need to send to stable. It is possible automation > will pick it up and make that decision for us. Automation shouldn't do that for mm/ patches because we asked. But fs/ material might sneak through. But it does appear that -stable won't need this.
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;
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(-)