The object of this series is to replace shiftfs with a proper uid/gid shifting bind mount instead of the shiftfs hack of introducing something that looks similar to an overlay filesystem to do it. The VFS still has the problem that in order to tell what vfsmount a dentry belongs to, struct path would have to be threaded everywhere struct dentry currently is. However, this patch is structured only to require a rethreading of notify_change. The rest of the knowledge that a shift is in operation is carried in the task structure by caching the unshifted credentials. Note that although it is currently dependent on the new configfd interface for bind mounts, only patch 3/3 relies on this, and the whole thing could be redone as a syscall or any other mechanism (depending on how people eventually want to fix the problem with the new fsconfig mechanism being unable to reconfigure bind mounts). The changes from v2 are I've added Amir's reviewed-by for the notify_change rethreading and I've implemented Serge's request for a base offset shift for the image. It turned out to be much harder to implement a simple linear shift than simply to do it through a different userns, so that's how I've done it. The userns you need to set up for the offset shifted image is one where the interior uid would see the shifted image as fake root. I've introduced an additional "ns" config parameter, which must be specified when building the allow shift mount point (so it's done by the admin, not by the unprivileged user). I've also taken care that the image shifted to zero (real root) is never visible in the filesystem. Patch 3/3 explains how to use the additional "ns" parameter. James --- James Bottomley (3): fs: rethread notify_change to take a path instead of a dentry fs: introduce uid/gid shifting bind mount fs: expose shifting bind mount to userspace drivers/base/devtmpfs.c | 8 ++- fs/attr.c | 131 ++++++++++++++++++++++++++++++++++++++-------- fs/bind.c | 105 +++++++++++++++++++++++++++++++++---- fs/cachefiles/interface.c | 6 ++- fs/coredump.c | 4 +- fs/ecryptfs/inode.c | 9 ++-- fs/exec.c | 3 +- fs/inode.c | 17 +++--- fs/internal.h | 2 + fs/mount.h | 3 ++ fs/namei.c | 114 +++++++++++++++++++++++++++++++++------- fs/namespace.c | 6 +++ fs/nfsd/vfs.c | 13 +++-- fs/open.c | 44 ++++++++++++---- fs/overlayfs/copy_up.c | 40 ++++++++------ fs/overlayfs/dir.c | 10 +++- fs/overlayfs/inode.c | 6 ++- fs/overlayfs/overlayfs.h | 2 +- fs/overlayfs/super.c | 3 +- fs/posix_acl.c | 4 +- fs/proc_namespace.c | 4 ++ fs/stat.c | 32 +++++++++-- fs/utimes.c | 2 +- include/linux/cred.h | 12 +++++ include/linux/fs.h | 7 ++- include/linux/mount.h | 4 +- include/linux/sched.h | 5 ++ kernel/capability.c | 9 +++- kernel/cred.c | 20 +++++++ 29 files changed, 507 insertions(+), 118 deletions(-) -- 2.16.4
