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mm/z3fold: fix z3fold_page_migrate races with z3fold_map

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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: 1f862989b0 ("mm/z3fold.c: support page migration")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Miaohe Lin 2022-04-29 14:40:43 +08:00 committed by akpm
parent 04094226d6
commit 943fb61dd6
1 changed files with 12 additions and 4 deletions
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16
mm/z3fold.c
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@ -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)
break;
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;
}