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mm/z3fold: avoid possible underflow in z3fold_alloc()

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It is not enough to just make sure the z3fold header is not larger than
the page size.  When z3fold header is equal to PAGE_SIZE, we would
underflow when check alloc size against PAGE_SIZE - ZHDR_SIZE_ALIGNED -
CHUNK_SIZE in z3fold_alloc().  Make sure there has remaining spaces for
its buddy to fix this theoretical issue.

Link: https://lkml.kernel.org/r/20210619093151.1492174-3-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Hillf Danton <hdanton@sina.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Miaohe Lin 2021-06-30 18:50:27 -07:00 • committed by Linus Torvalds
parent e3c0db4fec
commit 014284a081
1 changed files with 5 additions and 2 deletions
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7
mm/z3fold.c
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@ -1803,8 +1803,11 @@ static int __init init_z3fold(void)
{ {
int ret; int ret;
/* Make sure the z3fold header is not larger than the page size */ /*
BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE); * Make sure the z3fold header is not larger than the page size and
* there has remaining spaces for its buddy.
*/
BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
ret = z3fold_mount(); ret = z3fold_mount();
if (ret) if (ret)
return ret; return ret;