radix-tree: fix oops after radix_tree_iter_retry

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 00b17c526c1f4edf2dd1e256ab78f5cda4755363..f54be708220760f9a367f4a29ca1cbe7cfb7fba2 100644 (file)
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -400,7 +400,7 @@ 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;
@@ -434,9 +434,9 @@ 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))