On Tue, May 09, 2017 at 07:34:00PM -0500, Eric W. Biederman wrote: > Andrei Vagin <[email protected]> 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 <[email protected]> > > Cc: Eric W. Biederman <[email protected]> > > Signed-off-by: Andrei Vagin <[email protected]> > > --- > > 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 <linux/buffer_head.h> > > #include <linux/falloc.h> > > #include <linux/sched/signal.h> > > +#include <linux/proc_fs.h> > > +#include <linux/user_namespace.h> > > > > #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)
