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Date:   Tue, 10 Dec 2019 10:12:10 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Andreas Gruenbacher <agruenba@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Junichi Nomura <j-nomura@ce.jp.nec.com>,
        Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH] block: fix "check bi_size overflow before merge"
Message-ID: <20191210021210.GB25022@ming.t460p>
References: <20191209191114.17266-1-agruenba@redhat.com>
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On Mon, Dec 09, 2019 at 08:11:14PM +0100, Andreas Gruenbacher wrote:
> This partially reverts commit e3a5d8e386c3fb973fa75f2403622a8f3640ec06.
>=20
> Commit e3a5d8e386c3 ("check bi_size overflow before merge") adds a bio_fu=
ll
> check to __bio_try_merge_page.  This will cause __bio_try_merge_page to f=
ail
> when the last bi_io_vec has been reached.  Instead, what we want here is =
only
> the bi_size overflow check.
>=20
> Fixes: e3a5d8e386c3 ("block: check bi_size overflow before merge")
> Cc: stable@vger.kernel.org # v5.4+
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> ---
>  block/bio.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>=20
> diff --git a/block/bio.c b/block/bio.c
> index 9d54aa37ce6c..a5d75f6bf4c7 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -754,10 +754,12 @@ bool __bio_try_merge_page(struct bio *bio, struct p=
age *page,
>  =09if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
>  =09=09return false;
> =20
> -=09if (bio->bi_vcnt > 0 && !bio_full(bio, len)) {
> +=09if (bio->bi_vcnt > 0) {
>  =09=09struct bio_vec *bv =3D &bio->bi_io_vec[bio->bi_vcnt - 1];
> =20
>  =09=09if (page_is_mergeable(bv, page, len, off, same_page)) {
> +=09=09=09if (bio->bi_iter.bi_size > UINT_MAX - len)
> +=09=09=09=09return false;
>  =09=09=09bv->bv_len +=3D len;
>  =09=09=09bio->bi_iter.bi_size +=3D len;
>  =09=09=09return true;

page merging doesn't consume new bvec, so this patch is correct:

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming