From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrei Vagin Subject: Re: [PATCH] fs: add an ioctl to get an owning userns for a superblock Date: Wed, 10 May 2017 17:15:27 -0700 Message-ID: <20170511001526.GA7992@outlook.office365.com> References: <20170509231938.6467-1-avagin@openvz.org> <87k25psg7b.fsf@xmission.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <87k25psg7b.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: "Eric W. Biederman" Cc: Andrei Vagin , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux Containers , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, criu-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Alexander Viro , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.vger.kernel.org On Tue, May 09, 2017 at 07:34:00PM -0500, Eric W. Biederman wrote: > 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. Sure, we can. Do you know any place where to read more information about open_fs? I think I have heared a few times about this idea, but it would be good to get more details. Thanks, Andrei > > 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)