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    Subject[PATCH 4.2.y-ckt 110/273] radix-tree: fix oops after radix_tree_iter_retry
    Date
    4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Konstantin Khlebnikov <koct9i@gmail.com>

    commit 732042821cfa106b3c20b9780e4c60fee9d68900 upstream.

    Helper radix_tree_iter_retry() resets next_index to the current index.
    In following radix_tree_next_slot current chunk size becomes zero. This
    isn't checked and it tries to dereference null pointer in slot.

    Tagged iterator is fine because retry happens only at slot 0 where tag
    bitmask in iter->tags is filled with single bit.

    Fixes: 46437f9a554f ("radix-tree: fix race in gang lookup")
    Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
    Cc: Matthew Wilcox <willy@linux.intel.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Ohad Ben-Cohen <ohad@wizery.com>
    Cc: Jeremiah Mahler <jmmahler@gmail.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    include/linux/radix-tree.h | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
    index 1a2b227..5d5174b 100644
    --- a/include/linux/radix-tree.h
    +++ b/include/linux/radix-tree.h
    @@ -391,7 +391,7 @@ void **radix_tree_iter_retry(struct radix_tree_iter *iter)
    * @iter: pointer to radix tree iterator
    * Returns: current chunk size
    */
    -static __always_inline unsigned
    +static __always_inline long
    radix_tree_chunk_size(struct radix_tree_iter *iter)
    {
    return iter->next_index - iter->index;
    @@ -425,9 +425,9 @@ radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
    return slot + offset + 1;
    }
    } else {
    - unsigned size = radix_tree_chunk_size(iter) - 1;
    + long size = radix_tree_chunk_size(iter);

    - while (size--) {
    + while (--size > 0) {
    slot++;
    iter->index++;
    if (likely(*slot))
    --
    2.7.0
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