From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751035AbdEIXTp (ORCPT ); Tue, 9 May 2017 19:19:45 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:35245 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750767AbdEIXTn (ORCPT ); Tue, 9 May 2017 19:19:43 -0400 From: Andrei Vagin To: "Eric W . Biederman" Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, criu@openvz.org, Linux Containers , Andrei Vagin Subject: [PATCH] fs: add an ioctl to get an owning userns for a superblock Date: Tue, 9 May 2017 16:19:38 -0700 Message-Id: <20170509231938.6467-1-avagin@openvz.org> X-Mailer: git-send-email 2.9.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The introduced ioctl returns a file descriptor that refers to a owning user namespace for a superblock which is associated with a target file descriptor. EPERM is returned if the current process doesn't have CAP_SYS_ADMIN in the returned user namespace. This information is required to dump and restore mount namespaces. We need to know to which user namespace a superblock is belonged to. We already have the SIOCGSKNS ioctl for sockets to get a network namespace, so it looks reasonable to use the same interface for superblocks too. This functionality can be useful for users in order to understand a running system. Cc: Alexander Viro Cc: Eric W. Biederman Signed-off-by: Andrei Vagin --- fs/ioctl.c | 23 +++++++++++++++++++++++ include/uapi/linux/fs.h | 2 ++ 2 files changed, 25 insertions(+) diff --git a/fs/ioctl.c b/fs/ioctl.c index 569db68..22bbf37 100644 --- a/fs/ioctl.c +++ b/fs/ioctl.c @@ -16,6 +16,8 @@ #include #include #include +#include +#include #include "internal.h" @@ -614,6 +616,25 @@ static int ioctl_file_dedupe_range(struct file *file, void __user *arg) return ret; } +static struct ns_common *get_sb_userns(struct ns_common *ns_common) +{ + struct user_namespace *ns; + + ns = container_of(ns_common, struct user_namespace, ns); + + return &get_user_ns(ns)->ns; +} + +static int ioctl_fs_sb_userns(struct file *filp) +{ + struct super_block *sb = file_inode(filp)->i_sb; + + if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) + return -EPERM; + + return open_related_ns(&sb->s_user_ns->ns, get_sb_userns); +} + /* * When you add any new common ioctls to the switches above and below * please update compat_sys_ioctl() too. @@ -677,6 +698,8 @@ int do_vfs_ioctl(struct file *filp, unsigned int fd, unsigned int cmd, case FIDEDUPERANGE: return ioctl_file_dedupe_range(filp, argp); + case FS_IOC_SB_USERNS: + return ioctl_fs_sb_userns(filp); default: if (S_ISREG(inode->i_mode)) diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 33423aa..26ef2d5 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -246,6 +246,8 @@ struct fsxattr { #define FICLONE _IOW(0x94, 9, int) #define FICLONERANGE _IOW(0x94, 13, struct file_clone_range) #define FIDEDUPERANGE _IOWR(0x94, 54, struct file_dedupe_range) +/* Get a file descriptor to an owning userns for a superblock */ +#define FS_IOC_SB_USERNS _IOR('X', 55, int) #define FS_IOC_GETFLAGS _IOR('f', 1, long) #define FS_IOC_SETFLAGS _IOW('f', 2, long) -- 2.9.3