nfsd: containerize NFSd filesystem

This patch makes NFSD file system superblock to be created per net.
This makes possible to get proper network namespace from superblock instead of
using hard-coded "init_net".

Note: NFSd fs super-block holds network namespace. This garantees, that
network namespace won't disappear from underneath of it.
This, obviously, means, that in case of kill of a container's "init" (which is not a mount
namespace, but network namespace creator) netowrk namespace won't be
destroyed.
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

(cherry picked from commit 11f77942)
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

fs/nfsd/nfsctl.c

@@ -220,6 +220,7 @@ static ssize_t write_unlock_ip(struct file *file, char *buf, size_t size)
 	struct sockaddr *sap = (struct sockaddr *)&address;
 	size_t salen = sizeof(address);
 	char *fo_path;
+	struct net *net = file->f_dentry->d_sb->s_fs_info;
 
 	/* sanity check */
 	if (size == 0)
@@ -232,7 +233,7 @@ static ssize_t write_unlock_ip(struct file *file, char *buf, size_t size)
 	if (qword_get(&buf, fo_path, size) < 0)
 		return -EINVAL;
 
-	if (rpc_pton(&init_net, fo_path, size, sap, salen) == 0)
+	if (rpc_pton(net, fo_path, size, sap, salen) == 0)
 		return -EINVAL;
 
 	return nlmsvc_unlock_all_by_ip(sap);
@@ -396,7 +397,7 @@ static ssize_t write_threads(struct file *file, char *buf, size_t size)
 {
 	char *mesg = buf;
 	int rv;
-	struct net *net = &init_net;
+	struct net *net = file->f_dentry->d_sb->s_fs_info;
 
 	if (size > 0) {
 		int newthreads;
@@ -447,7 +448,7 @@ static ssize_t write_pool_threads(struct file *file, char *buf, size_t size)
 	int len;
 	int npools;
 	int *nthreads;
-	struct net *net = &init_net;
+	struct net *net = file->f_dentry->d_sb->s_fs_info;
 
 	mutex_lock(&nfsd_mutex);
 	npools = nfsd_nrpools(net);
@@ -797,7 +798,7 @@ static ssize_t __write_ports(struct file *file, char *buf, size_t size,
 static ssize_t write_ports(struct file *file, char *buf, size_t size)
 {
 	ssize_t rv;
-	struct net *net = &init_net;
+	struct net *net = file->f_dentry->d_sb->s_fs_info;
 
 	mutex_lock(&nfsd_mutex);
 	rv = __write_ports(file, buf, size, net);
@@ -1042,20 +1043,35 @@ static int nfsd_fill_super(struct super_block * sb, void * data, int silent)
 #endif
 		/* last one */ {""}
 	};
-	return simple_fill_super(sb, 0x6e667364, nfsd_files);
+	struct net *net = data;
+	int ret;
+
+	ret = simple_fill_super(sb, 0x6e667364, nfsd_files);
+	if (ret)
+		return ret;
+	sb->s_fs_info = get_net(net);
+	return 0;
 }
 
 static struct dentry *nfsd_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
-	return mount_single(fs_type, flags, data, nfsd_fill_super);
+	return mount_ns(fs_type, flags, current->nsproxy->net_ns, nfsd_fill_super);
+}
+
+static void nfsd_umount(struct super_block *sb)
+{
+	struct net *net = sb->s_fs_info;
+
+	kill_litter_super(sb);
+	put_net(net);
 }
 
 static struct file_system_type nfsd_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "nfsd",
 	.mount		= nfsd_mount,
-	.kill_sb	= kill_litter_super,
+	.kill_sb	= nfsd_umount,
 };
 
 #ifdef CONFIG_PROC_FS

fs/nfsd/nfssvc.c

@@ -724,7 +724,7 @@ int nfsd_pool_stats_open(struct inode *inode, struct file *file)
 int nfsd_pool_stats_release(struct inode *inode, struct file *file)
 {
 	int ret = seq_release(inode, file);
-	struct net *net = &init_net;
+	struct net *net = inode->i_sb->s_fs_info;
 
 	mutex_lock(&nfsd_mutex);
 	/* this function really, really should have been called svc_put() */