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Message-ID: <91b52aee40b0d6b4aeb94ea53e3e93a0504df5d8.camel@kernel.org>
Subject: Re: [PATCH v2 2/7] SUNRPC: Fix svcxdr_init_encode's buflen
 calculation
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Date:   Mon, 29 Aug 2022 08:51:41 -0400
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On Sun, 2022-08-28 at 14:50 -0400, Chuck Lever wrote:
> Commit 2825a7f90753 ("nfsd4: allow encoding across page boundaries")
> added an explicit computation of the remaining length in the rq_res
> XDR buffer.
>=20
> The computation appears to suffer from an "off-by-one" bug. Because
> buflen is too large by one page, XDR encoding can run off the end of
> the send buffer by eventually trying to use the struct page address
> in rq_page_end, which always contains NULL.
>=20
> Fixes: bddfdbcddbe2 ("NFSD: Extract the svcxdr_init_encode() helper")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/linux/sunrpc/svc.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 5a830b66f059..0ca8a8ffb47e 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -587,7 +587,7 @@ static inline void svcxdr_init_encode(struct svc_rqst=
 *rqstp)
>  	xdr->end =3D resv->iov_base + PAGE_SIZE - rqstp->rq_auth_slack;
>  	buf->len =3D resv->iov_len;
>  	xdr->page_ptr =3D buf->pages - 1;
> -	buf->buflen =3D PAGE_SIZE * (1 + rqstp->rq_page_end - buf->pages);
> +	buf->buflen =3D PAGE_SIZE * (rqstp->rq_page_end - buf->pages);
>  	buf->buflen -=3D rqstp->rq_auth_slack;
>  	xdr->rqst =3D NULL;
>  }
>=20
>=20

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