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Message-ID: <13dd5b2a5d90ebf4dd782d89a34cb2d7ce62f7e2.camel@kernel.org>
Subject: Re: [PATCH v3 5/6] NFSD: Protect against send buffer overflow in
 NFSv2 READ
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Date:   Fri, 02 Sep 2022 09:14:24 -0400
In-Reply-To: <166205941847.1435.15080240781458940273.stgit@manet.1015granger.net>
References: <166204973526.1435.6068003336048840051.stgit@manet.1015granger.net>
         <166205941847.1435.15080240781458940273.stgit@manet.1015granger.net>
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On Thu, 2022-09-01 at 15:10 -0400, Chuck Lever wrote:
> Since before the git era, NFSD has conserved the number of pages
> held by each nfsd thread by combining the RPC receive and send
> buffers into a single array of pages. This works because there are
> no cases where an operation needs a large RPC Call message and a
> large RPC Reply at the same time.
>=20
> Once an RPC Call has been received, svc_process() updates
> svc_rqst::rq_res to describe the part of rq_pages that can be
> used for constructing the Reply. This means that the send buffer
> (rq_res) shrinks when the received RPC record containing the RPC
> Call is large.
>=20
> A client can force this shrinkage on TCP by sending a correctly-
> formed RPC Call header contained in an RPC record that is
> excessively large. The full maximum payload size cannot be
> constructed in that case.
>=20
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfsproc.c |    1 +
>  1 file changed, 1 insertion(+)
>=20
> diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
> index ddb1902c0a18..4b19cc727ea5 100644
> --- a/fs/nfsd/nfsproc.c
> +++ b/fs/nfsd/nfsproc.c
> @@ -185,6 +185,7 @@ nfsd_proc_read(struct svc_rqst *rqstp)
>  		argp->count, argp->offset);
> =20
>  	argp->count =3D min_t(u32, argp->count, NFSSVC_MAXBLKSIZE_V2);
> +	argp->count =3D min_t(u32, argp->count, rqstp->rq_res.buflen);
> =20
>  	v =3D 0;
>  	len =3D argp->count;
>=20
>=20

Reviewed-by: Jeff Layton <jlayton@kernel.org>