Message-ID: <b6d8a8b96581d4f468d9277237113cb7b9e7fb10.camel@kernel.org>
Subject: Re: [PATCH v2 2/2] sunrpc: add bounds checking to
 svc_rqst_replace_page
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "dcritch@redhat.com" <dcritch@redhat.com>,
        "d.lesca@solinos.it" <d.lesca@solinos.it>,
        Al Viro <viro@zeniv.linux.org.uk>
Date:   Fri, 17 Mar 2023 18:10:15 -0400
In-Reply-To: <27346F71-367D-42DF-85AB-D168012F5C41@oracle.com>
References: <20230317171309.73607-1-jlayton@kernel.org>
         <20230317171309.73607-2-jlayton@kernel.org>
         <6F8F3C24-A043-443A-BBB7-E4788FBE29C9@oracle.com>
         <827d46876b57bec309164d4c9513bac523ad5843.camel@kernel.org>
         <F6CE9F70-628B-44D3-A8B1-D4EEBBA28B87@oracle.com>
         <c78fff223129f289214ceada0d82f6952e0d3a82.camel@kernel.org>
         <27346F71-367D-42DF-85AB-D168012F5C41@oracle.com>
Content-Type: text/plain; charset="ISO-8859-15"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) 
MIME-Version: 1.0
Precedence: bulk

On Fri, 2023-03-17 at 20:55 +0000, Chuck Lever III wrote:
>=20
> > On Mar 17, 2023, at 2:59 PM, Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > On Fri, 2023-03-17 at 18:08 +0000, Chuck Lever III wrote:
> > >=20
> > > > On Mar 17, 2023, at 2:04 PM, Jeff Layton <jlayton@kernel.org> wrote=
:
> > > >=20
> > > > On Fri, 2023-03-17 at 17:51 +0000, Chuck Lever III wrote:
> > > > > > On Mar 17, 2023, at 1:13 PM, Jeff Layton <jlayton@kernel.org> w=
rote:
> > > > > >=20
> > > > > > If rq_next_page ends up pointing outside the array, then we can
> > > > > > corrupt
> > > > > > memory when we go to change its value. Ensure that it hasn't st=
rayed
> > > > > > outside the array, and have svc_rqst_replace_page return -EIO
> > > > > > without
> > > > > > changing anything if it has.
> > > > > >=20
> > > > > > Fix up nfsd_splice_actor (the only caller) to handle this case =
by
> > > > > > either
> > > > > > returning an error or a short splice when this happens.
> > > > >=20
> > > > > IMO it's not worth the extra complexity to return a short splice.
> > > > > This is a "should never happen" scenario in a hot I/O path. Let's
> > > > > keep this code as simple as possible, and use unlikely() for the
> > > > > error cases in both nfsd_splice_actor and svc_rqst_replace_page()=
.
> > > > >=20
> > > >=20
> > > > Are there any issues with just returning an error even though we ha=
ve
> > > > successfully spliced some of the data into the buffer? I guess the
> > > > caller will just see an EIO or whatever instead of the short read i=
n
> > > > that case?
> > >=20
> > > NFSv4 READ is probably going to truncate the XDR buffer. I'm not
> > > sure NFSv3 is so clever, so you should test it.
> >=20
> > Honestly, I don't have the cycles to do that sort of fault injection
> > testing for this.
>=20
> nfsd_splice_actor() has never returned an error, so IMO it is
> necessary to confirm that when svc_rqst_replace_page() returns
> an error, it doesn't create further problems. I don't see how
> we can avoid some kind of simple fault injection while developing
> the fix.
>=20
> Tell you what, I can take it from here if you'd like.
>=20

Sure! All yours!

>=20
> > If you think handling it as a short read is overblown,
> > then tell me what you would like see here.
>=20
> It's not the short reads that bugs me, it's the additional
> code in a hot path that is worrisome.
>=20

I wouldn't think tracking some extra stuff on the stack would show up
much in profiles, but it's your call.

--=20
Jeff Layton <jlayton@kernel.org>