Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH] mm/swapfile: unuse_pte can map random data if swap read fails | From | Miaohe Lin <> | Date | Wed, 6 Apr 2022 16:47:52 +0800 |
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On 2022/4/4 22:11, Matthew Wilcox wrote: > On Mon, Apr 04, 2022 at 03:37:36PM +0200, David Hildenbrand wrote: >> On 01.04.22 09:29, Miaohe Lin wrote: >>> There is a bug in unuse_pte(): when swap page happens to be unreadable, >>> page filled with random data is mapped into user address space. The fix >>> is to check for PageUptodate and fail swapoff in case of error. >>> >>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >>> --- >>> mm/swapfile.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>> index 63c61f8b2611..e72a35de7a0f 100644 >>> --- a/mm/swapfile.c >>> +++ b/mm/swapfile.c >>> @@ -1795,6 +1795,10 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, >>> ret = 0; >>> goto out; >>> } >>> + if (unlikely(!PageUptodate(page))) { >>> + ret = -EIO; >>> + goto out; >>> + } >> >> Yeah, we have the same handling in do_swap_page(), whereby we send a >> SIGBUS because we're dealing with an actual access. >> >> Interestingly, folio_test_uptodate() states: >> >> "Anonymous and CoW folios are always uptodate." >> >> @Willy, is that true or is the swapin case not documented there? > > Why do we keep a !Uptodate page in the swap cache? If it can't be > read in from swap, I thought we just freed the page. Since Miaohe
We could free the bad page. But we still need a way to prevent user from accessing the wrong data.
> has observed that not happening, I guess it doesn't work that way, > but why not make it work that way?
How could we make it work that way? Could you please tell me in more detail? Or any suggestions?
Many thanks!
> > . >
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