NFS: Fix /proc/fs/nfsfs/servers and /proc/fs/nfsfs/volumes

The usage of pid_ns->child_reaper->nsproxy->net_ns in
nfs_server_list_open and nfs_client_list_open is not safe.

/proc for a pid namespace can remain mounted after the all of the
process in that pid namespace have exited.  There are also times
before the initial process in a pid namespace has started or after the
initial process in a pid namespace has exited where
pid_ns->child_reaper can be NULL or stale.  Making the idiom
pid_ns->child_reaper->nsproxy a double whammy of problems.

Luckily all that needs to happen is to move /proc/fs/nfsfs/servers and
/proc/fs/nfsfs/volumes under /proc/net to /proc/net/nfsfs/servers and
/proc/net/nfsfs/volumes and add a symlink from the original location,
and to use seq_open_net as it has been designed.

Cc: stable@vger.kernel.org
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index f415cbf9f6c3..2d2ebdfb0723 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -195,7 +195,16 @@ extern struct rpc_clnt *nfs4_find_or_create_ds_client(struct nfs_client *,
 #ifdef CONFIG_PROC_FS
 extern int __init nfs_fs_proc_init(void);
 extern void nfs_fs_proc_exit(void);
+extern int nfs_fs_proc_net_init(struct net *net);
+extern void nfs_fs_proc_net_exit(struct net *net);
 #else
+static inline int nfs_fs_proc_net_init(struct net *net)
+{
+	return 0;
+}
+static inline void nfs_fs_proc_net_exit(struct net *net)
+{
+}
 static inline int nfs_fs_proc_init(void)
 {
 	return 0;