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Subject: Re: [PATCH v3 3/6] NFSD: Protect against send buffer overflow in
 NFSv2 READDIR
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Date:   Fri, 02 Sep 2022 09:09:01 -0400
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         <166205940565.1435.7170548905174362083.stgit@manet.1015granger.net>
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On Thu, 2022-09-01 at 15:10 -0400, Chuck Lever wrote:
> Restore the previous limit on the @count argument to prevent a
> buffer overflow attack.
>=20
> Fixes: 53b1119a6e50 ("NFSD: Fix READDIR buffer overflow")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfsproc.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>=20
> diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
> index 7381972f1677..ddb1902c0a18 100644
> --- a/fs/nfsd/nfsproc.c
> +++ b/fs/nfsd/nfsproc.c
> @@ -567,12 +567,11 @@ static void nfsd_init_dirlist_pages(struct svc_rqst=
 *rqstp,
>  	struct xdr_buf *buf =3D &resp->dirlist;
>  	struct xdr_stream *xdr =3D &resp->xdr;
> =20
> -	count =3D clamp(count, (u32)(XDR_UNIT * 2), svc_max_payload(rqstp));
> -
>  	memset(buf, 0, sizeof(*buf));
> =20
>  	/* Reserve room for the NULL ptr & eof flag (-2 words) */
> -	buf->buflen =3D count - XDR_UNIT * 2;
> +	buf->buflen =3D clamp(count, (u32)(XDR_UNIT * 2), (u32)PAGE_SIZE);


> +	buf->buflen -=3D XDR_UNIT * 2;
>  	buf->pages =3D rqstp->rq_next_page;
>  	rqstp->rq_next_page++;
> =20
>=20
>=20

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