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authorMiaohe Lin <linmiaohe@huawei.com>2022-04-29 14:40:43 +0800
committerakpm <akpm@linux-foundation.org>2022-05-27 09:33:44 -0700
commit943fb61dd66f475c25b1ef5dddb647070f2e89a1 (patch)
tree0f867eb3f6ae071634813a1284fa8833eb2eec4d
parent04094226d6ce8c0cb590891e13872109aa6722f1 (diff)
downloadlinux-943fb61dd66f475c25b1ef5dddb647070f2e89a1.tar.bz2
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: 1f862989b04a ("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>
-rw-r--r--mm/z3fold.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/mm/z3fold.c b/mm/z3fold.c
index a7769befd74e..f41f8b0d9e9a 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -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;
}