Re: [PATCH 1/3] zram: fix operator precedence to get offset

From	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/3] zram: fix operator precedence to get offset
Date	2017-04-17 03:30 +0200
Message-ID	<tx3El-2zi-1@gated-at.bofh.it> (permalink)
References	<tvAEp-3qZ-3@gated-at.bofh.it> <tw1EC-5pR-5@gated-at.bofh.it> <twbuh-2Mv-19@gated-at.bofh.it>
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Hello,

On (04/15/17 00:33), Minchan Kim wrote:
> On Fri, Apr 14, 2017 at 02:07:47PM +0900, Sergey Senozhatsky wrote:
> > On (04/13/17 09:17), Minchan Kim wrote:
> > [..]
> > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > > index 9e2199060040..83c38a123242 100644
> > > --- a/drivers/block/zram/zram_drv.c
> > > +++ b/drivers/block/zram/zram_drv.c
> > > @@ -930,7 +930,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
> > >  	}
> > >  
> > >  	index = sector >> SECTORS_PER_PAGE_SHIFT;
> > > -	offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT;
> > > +	offset = (sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
> > 
> > sorry, can it actually produce different results?
> 
> I got your point. Actually, offset was wrong but rw_page is called
> with PAGE_SIZE io while that offset is related to only partial io
> (non-PAGEE size io). IOW, although the wrong offset it is never used
> in functions.
> 
> To find subtle corruption in ppc64, I added some debug code to
> catch up wrong buffer overflow and found it with other bugs but
> didn't prove the specific case is valid case or not. Good catch, Sergey!
> 
> However, it should be *fixed* to prevent confusion in future but surely,
> no need to go to the stable. I will send reply to Greg to prevent merging
> it to *stable* when he send review asking to merge.

cool. thanks!

> And next week I will send another fix which *maybe* removes code to get the
> offset in zram_rw_page.

sounds interesting!

	-ss

Thread

[PATCH 1/3] zram: fix operator precedence to get offset Minchan Kim <minchan@kernel.org> - 2017-04-13 02:20 +0200
  [PATCH 3/3] zsmalloc: expand class bit Minchan Kim <minchan@kernel.org> - 2017-04-13 02:20 +0200
  [PATCH 2/3] zram: do not use copy_page with non-page alinged address Minchan Kim <minchan@kernel.org> - 2017-04-13 02:20 +0200
    Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged  address Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-14 07:50 +0200
      Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged  address Minchan Kim <minchan@kernel.org> - 2017-04-14 17:50 +0200
    Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged  address Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 03:50 +0200
  Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-14 07:10 +0200
    Re: [PATCH 1/3] zram: fix operator precedence to get offset Minchan Kim <minchan@kernel.org> - 2017-04-14 17:40 +0200
      Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 03:30 +0200
        Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 04:00 +0200
          Re: [PATCH 1/3] zram: fix operator precedence to get offset Minchan Kim <minchan@kernel.org> - 2017-04-17 04:20 +0200
            Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 13:00 +0200
              Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 13:00 +0200
              Re: [PATCH 1/3] zram: fix operator precedence to get offset Minchan Kim <minchan@kernel.org> - 2017-04-18 02:00 +0200
                Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-18 04:00 +0200
                Re: [PATCH 1/3] zram: fix operator precedence to get offset Minchan Kim <minchan@kernel.org> - 2017-04-18 04:50 +0200
  Re: [PATCH 1/3] zram: fix operator precedence to get offset Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-04-17 03:30 +0200

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