Commit 943fb61d authored by Miaohe Lin's avatar Miaohe Lin Committed by Andrew Morton
Browse files

mm/z3fold: fix z3fold_page_migrate races with z3fold_map 

Think about the below scenario:

CPU1				CPU2
 z3fold_page_migrate		z3fold_map
  z3fold_page_trylock
  ...
  z3fold_page_unlock
  /* slots still points to old zhdr*/
				 get_z3fold_header
				  get slots from handle
				  get old zhdr from slots
				  z3fold_page_trylock
				  return *old* zhdr
  encode_handle(new_zhdr, FIRST|LAST|MIDDLE)
  put_page(page) /* zhdr is freed! */
				 but zhdr is still used by caller!

z3fold_map can map freed z3fold page and lead to use-after-free bug.  To
fix it, we add PAGE_MIGRATED to indicate z3fold page is migrated and soon
to be released.  So get_z3fold_header won't return such page.

Link: https://lkml.kernel.org/r/20220429064051.61552-10-linmiaohe@huawei.com


Fixes: 1f862989 ("mm/z3fold.c: support page migration")
Signed-off-by: default avatarMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: default avatarVitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 04094226

mm/z3fold.c

+12 −4
Original line number Diff line number Diff line
@@ -181,6 +181,7 @@ enum z3fold_page_flags { 
	NEEDS_COMPACTING,

	PAGE_STALE,

	PAGE_CLAIMED, /* by either reclaim or free */

	PAGE_MIGRATED, /* page is migrated and soon to be released */

};



/*
@@ -270,8 +271,13 @@ static inline struct z3fold_header *get_z3fold_header(unsigned long handle) 
			zhdr = (struct z3fold_header *)(addr & PAGE_MASK);

			locked = z3fold_page_trylock(zhdr);

			read_unlock(&slots->lock);

			if (locked)

			if (locked) {

				struct page *page = virt_to_page(zhdr);



				if (!test_bit(PAGE_MIGRATED, &page->private))

					break;

				z3fold_page_unlock(zhdr);

			}

			cpu_relax();

		} while (true);

	} else {
@@ -389,6 +395,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page, bool headless, 
	clear_bit(NEEDS_COMPACTING, &page->private);

	clear_bit(PAGE_STALE, &page->private);

	clear_bit(PAGE_CLAIMED, &page->private);

	clear_bit(PAGE_MIGRATED, &page->private);

	if (headless)

		return zhdr;
@@ -1576,7 +1583,7 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa 
	new_zhdr = page_address(newpage);

	memcpy(new_zhdr, zhdr, PAGE_SIZE);

	newpage->private = page->private;

	page->private = 0;

	set_bit(PAGE_MIGRATED, &page->private);

	z3fold_page_unlock(zhdr);

	spin_lock_init(&new_zhdr->page_lock);

	INIT_WORK(&new_zhdr->work, compact_page_work);
@@ -1606,7 +1613,8 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa 


	queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);



	clear_bit(PAGE_CLAIMED, &page->private);

	/* PAGE_CLAIMED and PAGE_MIGRATED are cleared now. */

	page->private = 0;

	put_page(page);

	return 0;

}