linux-kernel - Re: [PATCH v4 1/4] lib/scatterlist: Fix mapping iterator when sg->offset is greater than PAGE

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Message-ID: <20190625012059.albyfaca73uoaoxr@gondor.apana.org.au>
Date:   Tue, 25 Jun 2019 09:20:59 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Imre Deak <imre.deak@...el.com>
Cc:     Christophe Leroy <christophe.leroy@....fr>,
        "David S. Miller" <davem@...emloft.net>, horia.geanta@....com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 1/4] lib/scatterlist: Fix mapping iterator when
 sg->offset is greater than PAGE_SIZE

On Mon, Jun 24, 2019 at 08:35:33PM +0300, Imre Deak wrote:
> Hi,
> 
> On Thu, Jun 20, 2019 at 02:02:21PM +0800, Herbert Xu wrote:
> > On Mon, Jun 17, 2019 at 09:15:02PM +0000, Christophe Leroy wrote:
> > > All mapping iterator logic is based on the assumption that sg->offset
> > > is always lower than PAGE_SIZE.
> > > 
> > > But there are situations where sg->offset is such that the SG item
> > > is on the second page.
> 
> could you explain how sg->offset becomes >= PAGE_SIZE?

The network stack can produce SG list elements that are longer
than PAGE_SIZE.  If you the iterate over it one page at a time
then the offset can exceed PAGE_SIZE.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt