Patch "blk-mq: fix use-after-free in blk_mq_free_tag_set()" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

blk-mq: fix use-after-free in blk_mq_free_tag_set()

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
blk-mq-fix-use-after-free-in-blk_mq_free_tag_set.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Junichi Nomura <[email protected]>
Date: Wed, 14 Oct 2015 05:02:15 +0000
Subject: blk-mq: fix use-after-free in blk_mq_free_tag_set()

From: Junichi Nomura <[email protected]>

commit f42d79ab67322e51b92dd7aa965e310c71352a64 upstream.

tags is freed in blk_mq_free_rq_map() and should not be used after that. The problem doesn't manifest if CONFIG_CPUMASK_OFFSTACK is false because free_cpumask_var() is nop.

tags->cpumask is allocated in blk_mq_init_tags() so it's natural to free cpumask in its counter part, blk_mq_free_tags().

---
 block/blk-mq-tag.c |    1 +
 block/blk-mq.c     |    4 +---
 2 files changed, 2 insertions(+), 3 deletions(-)

@@ -628,6 +628,7 @@ void blk_mq_free_tags(struct blk_mq_tags
 {
 	bt_free(&tags->bitmap_tags);
 	bt_free(&tags->breserved_tags);
+	free_cpumask_var(tags->cpumask);
 	kfree(tags);
 }
 

@@ -2263,10 +2263,8 @@ void blk_mq_free_tag_set(struct blk_mq_t
 	int i;
 
 	for (i = 0; i < set->nr_hw_queues; i++) {
-		if (set->tags[i]) {
+		if (set->tags[i])
 			blk_mq_free_rq_map(set, set->tags[i], i);
-			free_cpumask_var(set->tags[i]->cpumask);
-		}
 	}
 
 	kfree(set->tags);

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/blk-mq-fix-use-after-free-in-blk_mq_free_tag_set.patch