Re: [PATCH] NFSD: nfsctl: remove read permission of filehandle

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2024-03-19 at 18:47 +0800, Chen Hanxiao wrote:
> As write_filehandle can't accept zero-bytes writting, 
> remove read permission of /proc/fs/nfsd/filehandle
> 
> Signed-off-by: Chen Hanxiao <chenhx.fnst@fujitsu.com>
> ---
>  fs/nfsd/nfsctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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] = {"unlock_filesystem",
>  					&transaction_ops, S_IWUSR|S_IRUSR},
> -		[NFSD_Fh] = {"filehandle", &transaction_ops, S_IWUSR|S_IRUSR},
> +		[NFSD_Fh] = {"filehandle", &transaction_ops, S_IWUSR},
>  		[NFSD_Threads] = {"threads", &transaction_ops, S_IWUSR|S_IRUSR},
>  		[NFSD_Pool_Threads] = {"pool_threads", &transaction_ops, S_IWUSR|S_IRUSR},
>  		[NFSD_Pool_Stats] = {"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 = 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.
-- 
Jeff Layton <jlayton@kernel.org>