[PATCH] mm/z3fold.c: don't try to use buddy slots after free

[Vitaly Wool <vitalywool@gmail.com>]

From fd87fdc38ea195e5a694102a57bd4d59fc177433 Mon Sep 17 00:00:00 2001
From: Vitaly Wool <vitalywool@gmail.com>
Date: Mon, 8 Jul 2019 13:41:02 +0200
[PATCH] mm/z3fold: don't try to use buddy slots after free

As reported by Henry Burns:

Running z3fold stress testing with address sanitization
showed zhdr->slots was being used after it was freed.

z3fold_free(z3fold_pool, handle)
  free_handle(handle)
    kmem_cache_free(pool->c_handle, zhdr->slots)
  release_z3fold_page_locked_list(kref)
    __release_z3fold_page(zhdr, true)
      zhdr_to_pool(zhdr)
        slots_to_pool(zhdr->slots)  *BOOM*

To fix this, add pointer to the pool back to z3fold_header and modify
zhdr_to_pool to return zhdr->pool.

Fixes: 7c2b8baa61fe  ("mm/z3fold.c: add structure for buddy handles")

Reported-by: Henry Burns <henryburns@google.com>
Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
---
 mm/z3fold.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 985732c8b025..e1686bf6d689 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -101,6 +101,7 @@ struct z3fold_buddy_slots {
  * @refcount:		reference count for the z3fold page
  * @work:		work_struct for page layout optimization
  * @slots:		pointer to the structure holding buddy slots
+ * @pool:		pointer to the containing pool
  * @cpu:		CPU which this page "belongs" to
  * @first_chunks:	the size of the first buddy in chunks, 0 if free
  * @middle_chunks:	the size of the middle buddy in chunks, 0 if free
@@ -114,6 +115,7 @@ struct z3fold_header {
 	struct kref refcount;
 	struct work_struct work;
 	struct z3fold_buddy_slots *slots;
+	struct z3fold_pool *pool;
 	short cpu;
 	unsigned short first_chunks;
 	unsigned short middle_chunks;
@@ -320,6 +322,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page,
 	zhdr->start_middle = 0;
 	zhdr->cpu = -1;
 	zhdr->slots = slots;
+	zhdr->pool = pool;
 	INIT_LIST_HEAD(&zhdr->buddy);
 	INIT_WORK(&zhdr->work, compact_page_work);
 	return zhdr;
@@ -426,7 +429,7 @@ static enum buddy handle_to_buddy(unsigned long handle)
 
 static inline struct z3fold_pool *zhdr_to_pool(struct z3fold_header *zhdr)
 {
-	return slots_to_pool(zhdr->slots);
+	return zhdr->pool;
 }
 
 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
-- 
2.17.1