[dm-devel] fix an integer overflow in __blkdev_sectors_to_bio_pages
Mike Snitzer
snitzer at redhat.com
Mon Sep 11 14:58:33 UTC 2017
On Mon, Aug 14 2017 at 8:01pm -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:
>
>
> On Mon, 14 Aug 2017, Damien Le Moal wrote:
>
> > On Sun, 2017-08-13 at 22:47 -0400, Mikulas Patocka wrote:
> > >
> > > On Wed, 9 Aug 2017, hch at lst.de wrote:
> > >
> > > > Does commit 615d22a51c04856efe62af6e1d5b450aaf5cc2c0
> > > > "block: Fix __blkdev_issue_zeroout loop" fix the issue for you?
> > > >
> > > > --
> > > > dm-devel mailing list
> > > > dm-devel at redhat.com
> > > > https://www.redhat.com/mailman/listinfo/dm-devel
> > >
> > > I think that patch is incorrect. sector_t may be a 32-bit type and
> > > nr_sects << 9 may overflow.
> > >
> > > static unsigned int __blkdev_sectors_to_bio_pages(sector_t nr_sects)
> > > {
> > > sector_t bytes = (nr_sects << 9) + PAGE_SIZE - 1;
> > >
> > > return min(bytes >> PAGE_SHIFT, (sector_t)BIO_MAX_PAGES);
> > > }
> > >
> > > Mikulas
> >
> > Mikulas,
> >
> > Does the follwing patch fix the problem ?
> >
> > From 947b3cf41e759b2b23f684e215e651d0c8037f88 Mon Sep 17 00:00:00 2001
> > From: Damien Le Moal <damien.lemoal at wdc.com>
> > Date: Mon, 14 Aug 2017 13:01:16 +0900
> > Subject: [PATCH] block: Fix __blkdev_sectors_to_bio_pages()
> >
> > On 32bit systems where sector_t is a 32bits type, the calculation of
> > bytes may overflow. Use the u64 type for the local calculation to avoid
> > overflows.
> >
> > Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
> > ---
> > block/blk-lib.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > index 3fe0aec90597..ccf22dba21f0 100644
> > --- a/block/blk-lib.c
> > +++ b/block/blk-lib.c
> > @@ -269,9 +269,9 @@ static int __blkdev_issue_write_zeroes(struct block_device
> > *bdev,
> > */
> > static unsigned int __blkdev_sectors_to_bio_pages(sector_t nr_sects)
> > {
> > - sector_t bytes = (nr_sects << 9) + PAGE_SIZE - 1;
> > + u64 bytes = ((u64)nr_sects << 9) + PAGE_SIZE - 1;
> >
> > - return min(bytes >> PAGE_SHIFT, (sector_t)BIO_MAX_PAGES);
> > + return min(bytes >> PAGE_SHIFT, (u64)BIO_MAX_PAGES);
> > }
> >
>
> It's OK, but it is not needed to use 64-bit arithmetic here if all we need
> is to shift the value right. Here I submit a simplified patch, using the
> macro DIV_ROUND_UP_SECTOR_T (the macro gets optimized to just an addition
> and right shift).
>
>
>
> From: Mikulas Patocka <mpatocka at redhat.com>
>
> Fix possible integer overflow in __blkdev_sectors_to_bio_pages if sector_t
> is 32-bit.
>
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> Fixes: 615d22a51c04 ("block: Fix __blkdev_issue_zeroout loop")
>
> ---
> block/blk-lib.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/block/blk-lib.c
> ===================================================================
> --- linux-2.6.orig/block/blk-lib.c
> +++ linux-2.6/block/blk-lib.c
> @@ -269,9 +269,9 @@ static int __blkdev_issue_write_zeroes(s
> */
> static unsigned int __blkdev_sectors_to_bio_pages(sector_t nr_sects)
> {
> - sector_t bytes = (nr_sects << 9) + PAGE_SIZE - 1;
> + sector_t pages = DIV_ROUND_UP_SECTOR_T(nr_sects, PAGE_SIZE / 512);
>
> - return min(bytes >> PAGE_SHIFT, (sector_t)BIO_MAX_PAGES);
> + return min(pages, (sector_t)BIO_MAX_PAGES);
> }
>
> /**
>
Jens can you pick this up?
Also here:
https://patchwork.kernel.org/patch/9900407/
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