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Message-ID: <3dc4e3e0a730795bb803ce4cde66b45ed428765a.camel@kernel.org>
Subject: Re: [PATCH] NFSD: nfsctl: remove read permission of filehandle
From: Jeff Layton <jlayton@kernel.org>
To: Chen Hanxiao <chenhx.fnst@fujitsu.com>, Chuck Lever
 <chuck.lever@oracle.com>,  Neil Brown <neilb@suse.de>, Olga Kornievskaia
 <kolga@netapp.com>, Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey
 <tom@talpey.com>
Cc: linux-nfs@vger.kernel.org
Date: Tue, 19 Mar 2024 09:09:12 -0400
In-Reply-To: <20240319104714.1178-1-chenhx.fnst@fujitsu.com>
References: <20240319104714.1178-1-chenhx.fnst@fujitsu.com>
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On Tue, 2024-03-19 at 18:47 +0800, Chen Hanxiao wrote:
> As write_filehandle can't accept zero-bytes writting,=20
> remove read permission of /proc/fs/nfsd/filehandle
>=20
> Signed-off-by: Chen Hanxiao <chenhx.fnst@fujitsu.com>
> ---
>  fs/nfsd/nfsctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index ecd18bffeebc..da1387f1e30a 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -1346,7 +1346,7 @@ static int nfsd_fill_super(struct super_block *sb, =
struct fs_context *fc)
>  					&transaction_ops, S_IWUSR|S_IRUSR},
>  		[NFSD_FO_UnlockFS] =3D {"unlock_filesystem",
>  					&transaction_ops, S_IWUSR|S_IRUSR},
> -		[NFSD_Fh] =3D {"filehandle", &transaction_ops, S_IWUSR|S_IRUSR},
> +		[NFSD_Fh] =3D {"filehandle", &transaction_ops, S_IWUSR},
>  		[NFSD_Threads] =3D {"threads", &transaction_ops, S_IWUSR|S_IRUSR},
>  		[NFSD_Pool_Threads] =3D {"pool_threads", &transaction_ops, S_IWUSR|S_I=
RUSR},
>  		[NFSD_Pool_Stats] =3D {"pool_stats", &pool_stats_operations, S_IRUGO},


I don't think we can do this. mountd does this to get the rootfh for an
exported fs and it'll probably start failing if it can't open that file
for read:

    f =3D open("/proc/fs/nfsd/filehandle", O_RDWR);

That write_filehandle interface sure is weird though. Could we get rid
of it by teaching cache_get_filehandle how to use name_to_handle_at
instead? That would be a lot cleaner and would get rid of yet another
dependency on /proc/fs/nfsd.
--=20
Jeff Layton <jlayton@kernel.org>