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References: <20210609210729.254578-1-Anna.Schumaker@Netapp.com>
 <20210614231440.GD16500@fieldses.org> <20210812203248.GA907@fieldses.org>
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From:   Anna Schumaker <schumaker.anna@gmail.com>
Date:   Thu, 26 Aug 2021 15:44:32 -0400
Message-ID: <CAFX2Jf=b1JwPRaC35rKbX5bD821h1dsEj6opYW9eZET171Zd6A@mail.gmail.com>
Subject: Re: [PATCH] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     Trond Myklebust <Trond.Myklebust@hammerspace.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Thu, Aug 12, 2021 at 4:32 PM J. Bruce Fields <bfields@fieldses.org> wrote:
>
> On Mon, Jun 14, 2021 at 07:14:40PM -0400, bfields wrote:
> > On Wed, Jun 09, 2021 at 05:07:29PM -0400, schumaker.anna@gmail.com wrote:
> > > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > >
> > > This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
> >
> > Yep, I hit a KASAN warning here every time, and this fixes it,
> > thanks.--b.
>
> By the way, config NFS_V4_2_READ_PLUS still says:
>
>         This is intended for developers only. The READ_PLUS operation
>         has been shown to have issues under specific conditions and
>         should not be used in production.
>
> But this warning was the only thing I was seeing.  Is there another
> known issue remaining?

I think it was an issue around using lseek to generate the reply. The
file contents could change between each call, leading to inconsistent
results (and a new failing xfstest that previously passed)

Anna

>
> --b.
>
> >
> > > I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
> > > greater than the number of pages in the array. So let's just return
> > > early if we're setting base to a point at the end of the page data and
> > > let xdr_set_tail_base() handle setting up the buffer pointers instead.
> > >
> > > Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > > ---
> > >  net/sunrpc/xdr.c | 7 +++----
> > >  1 file changed, 3 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> > > index 3964ff74ee51..ca10ba2626f2 100644
> > > --- a/net/sunrpc/xdr.c
> > > +++ b/net/sunrpc/xdr.c
> > > @@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
> > >     void *kaddr;
> > >
> > >     maxlen = xdr->buf->page_len;
> > > -   if (base >= maxlen) {
> > > -           base = maxlen;
> > > -           maxlen = 0;
> > > -   } else
> > > +   if (base >= maxlen)
> > > +           return 0;
> > > +   else
> > >             maxlen -= base;
> > >     if (len > maxlen)
> > >             len = maxlen;
> > > --
> > > 2.32.0