[4.2.y-ckt stable] Patch "radix-tree: fix oops after radix_tree_iter_retry" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    radix-tree: fix oops after radix_tree_iter_retry

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From 11db327740da88a685efd01c7ea71462a199bb33 Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <koct9i at gmail.com>
Date: Fri, 5 Feb 2016 15:37:01 -0800
Subject: radix-tree: fix oops after radix_tree_iter_retry

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 at gmail.com>
Cc: Matthew Wilcox <willy at linux.intel.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Ohad Ben-Cohen <ohad at wizery.com>
Cc: Jeremiah Mahler <jmmahler at gmail.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at 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