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Disable rootless mode except RootlessCgMgr when executed as the root in userns

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This PR decomposes `libcontainer/configs.Config.Rootless bool` into `RootlessEUID bool` and
`RootlessCgroups bool`, so as to make "runc-in-userns" to be more compatible with "rootful" runc.

`RootlessEUID` denotes that runc is being executed as a non-root user (euid != 0) in
the current user namespace. `RootlessEUID` is almost identical to the former `Rootless`
except cgroups stuff.

`RootlessCgroups` denotes that runc is unlikely to have the full access to cgroups.
`RootlessCgroups` is set to false if runc is executed as the root (euid == 0) in the initial namespace.
Otherwise `RootlessCgroups` is set to true.
(Hint: if `RootlessEUID` is true, `RootlessCgroups` becomes true as well)

When runc is executed as the root (euid == 0) in an user namespace (e.g. by Docker-in-LXD, Podman, Usernetes),
`RootlessEUID` is set to false but `RootlessCgroups` is set to true.
So, "runc-in-userns" behaves almost same as "rootful" runc except that cgroups errors are ignored.

This PR does not have any impact on CLI flags and `state.json`.

Note about CLI:
* Now `runc --rootless=(auto|true|false)` CLI flag is only used for setting `RootlessCgroups`.
* Now `runc spec --rootless` is only required when `RootlessEUID` is set to true.
  For runc-in-userns, `runc spec`  without `--rootless` should work, when sufficient numbers of
  UID/GID are mapped.

Note about `$XDG_RUNTIME_DIR` (e.g. `/run/user/1000`):
* `$XDG_RUNTIME_DIR` is ignored if runc is being executed as the root (euid == 0) in the initial namespace, for backward compatibility.
  (`/run/runc` is used)
* If runc is executed as the root (euid == 0) in an user namespace, `$XDG_RUNTIME_DIR` is honored if `$USER != "" && $USER != "root"`.
  This allows unprivileged users to allow execute runc as the root in userns, without mounting writable `/run/runc`.

Note about `state.json`:
* `rootless` is set to true when `RootlessEUID == true && RootlessCgroups == true`.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
This commit is contained in:
Akihiro Suda
2018-07-05 15:28:21 +09:00
parent 70ca035aa6
commit 06f789cf26
22 changed files with 231 additions and 198 deletions
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main.go
+3 -8
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@@ -63,13 +63,8 @@ func main() {
app.Version = strings.Join(v, "\n")
root := "/run/runc"
rootless, err := isRootless(nil)
if err != nil {
fatal(err)
}
if rootless {
runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
if runtimeDir != "" {
if shouldHonorXDGRuntimeDir() {
if runtimeDir := os.Getenv("XDG_RUNTIME_DIR"); runtimeDir != "" {
root = runtimeDir + "/runc"
// According to the XDG specification, we need to set anything in
// XDG_RUNTIME_DIR to have a sticky bit if we don't want it to get
@@ -115,7 +110,7 @@ func main() {
cli.StringFlag{
Name: "rootless",
Value: "auto",
Usage: "enable rootless mode ('true', 'false', or 'auto')",
Usage: "ignore cgroup permission errors ('true', 'false', or 'auto')",
},
}
app.Commands = []cli.Command{