From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: [PATCH] fs: add an ioctl to get an owning userns for a superblock Date: Tue, 09 May 2017 19:34:00 -0500 Message-ID: <87k25psg7b.fsf@xmission.com> References: <20170509231938.6467-1-avagin@openvz.org> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <20170509231938.6467-1-avagin-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org> (Andrei Vagin's message of "Tue, 9 May 2017 16:19:38 -0700") Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrei Vagin Cc: Alexander Viro , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, criu-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Linux Containers List-Id: linux-api@vger.kernel.org Andrei Vagin writes: > 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. This will probably work. And the capability check eases any concerns I might have that this would be a trivial information leak. That said can we hold off just a little bit. If open_fs work actually turns into a real interface that would seem to be the perfect place to stick this functionality. Eric > > 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)