dotcloud/docker

package mountopts

import (
    "golang.org/x/sys/unix"
)

// UnprivilegedMountFlags gets the set of mount flags that are set on the mount that contains the given
// path and are locked by CL_UNPRIVILEGED. This is necessary to ensure that
// bind-mounting "with options" will not fail with user namespaces, due to
// kernel restrictions that require user namespace mounts to preserve
// CL_UNPRIVILEGED locked flags.
//
// TODO: Move to github.com/moby/sys/mount, and update BuildKit copy of this code as well (https://github.com/moby/buildkit/blob/v0.13.0/util/rootless/mountopts/mountopts_linux.go#L11-L18)
func UnprivilegedMountFlags(path string) ([]string, error) {
    var statfs unix.Statfs_t
    if err := unix.Statfs(path, &statfs); err != nil {
        return nil, err
    }

    // The set of keys come from https://github.com/torvalds/linux/blob/v4.13/fs/namespace.c#L1034-L1048.
    unprivilegedFlags := map[uint64]string{
        unix.MS_RDONLY:     "ro",
        unix.MS_NODEV:      "nodev",
        unix.MS_NOEXEC:     "noexec",
        unix.MS_NOSUID:     "nosuid",
        unix.MS_NOATIME:    "noatime",
        unix.MS_RELATIME:   "relatime",
        unix.MS_NODIRATIME: "nodiratime",
    }

    var flags []string
    for mask, flag := range unprivilegedFlags {
        if uint64(statfs.Flags)&mask == mask {
            flags = append(flags, flag)
        }
    }

    return flags, nil
}