proc: Convert proc_mount to use mount_ns.

Move the call of get_pid_ns, the call of proc_parse_options, and
the setting of s_iflags into proc_fill_super so that mount_ns
can be used.

Convert proc_mount to call mount_ns and remove the now unnecessary
code.

Acked-by: Seth Forshee <seth.forshee@canonical.com>
Reviewed-by: Djalal Harouni <tixxdz@gmail.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 78fa452..f4817ef 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -457,12 +457,17 @@
 	return inode;
 }
 
-int proc_fill_super(struct super_block *s)
+int proc_fill_super(struct super_block *s, void *data, int silent)
 {
+	struct pid_namespace *ns = get_pid_ns(s->s_fs_info);
 	struct inode *root_inode;
 	int ret;
 
-	s->s_iflags |= SB_I_USERNS_VISIBLE;
+	if (!proc_parse_options(data, ns))
+		return -EINVAL;
+
+	/* User space would break if executables appear on proc */
+	s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC;
 	s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC;
 	s->s_blocksize = 1024;
 	s->s_blocksize_bits = 10;