• Eric W. Biederman's avatar
    userns: Support fuse interacting with multiple user namespaces · 499dcf20
    Eric W. Biederman authored
    
    
    Use kuid_t and kgid_t in struct fuse_conn and struct fuse_mount_data.
    
    The connection between between a fuse filesystem and a fuse daemon is
    established when a fuse filesystem is mounted and provided with a file
    descriptor the fuse daemon created by opening /dev/fuse.
    
    For now restrict the communication of uids and gids between the fuse
    filesystem and the fuse daemon to the initial user namespace.  Enforce
    this by verifying the file descriptor passed to the mount of fuse was
    opened in the initial user namespace.  Ensuring the mount happens in
    the initial user namespace is not necessary as mounts from non-initial
    user namespaces are not yet allowed.
    
    In fuse_req_init_context convert the currrent fsuid and fsgid into the
    initial user namespace for the request that will be sent to the fuse
    daemon.
    
    In fuse_fill_attr convert the uid and gid passed from the fuse daemon
    from the initial user namespace into kuids and kgids.
    
    In iattr_to_fattr called from fuse_setattr convert kuids and kgids
    into the uids and gids in the initial user namespace before passing
    them to the fuse filesystem.
    
    In fuse_change_attributes_common called from fuse_dentry_revalidate,
    fuse_permission, fuse_geattr, and fuse_setattr, and fuse_iget convert
    the uid and gid from the fuse daemon into a kuid and a kgid to store
    on the fuse inode.
    
    By default fuse mounts are restricted to task whose uid, suid, and
    euid matches the fuse user_id and whose gid, sgid, and egid matches
    the fuse group id.  Convert the user_id and group_id mount options
    into kuids and kgids at mount time, and use uid_eq and gid_eq to
    compare the in fuse_allow_task.
    
    Cc: Miklos Szeredi <miklos@szeredi.hu>
    Acked-by: default avatarSerge Hallyn <serge.hallyn@canonical.com>
    Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
    499dcf20