fix: randomize lxc container names

In situations where concurrent stacker runs are happening on a system,
and they are building containers with the same name,
and they are being done inside a mount namespace,
and the path name given as the roots dir is the same,
but the actual mounted volume is different,

then both stackers will be able to acquire the file lock at
$rootdir/.lock, and will go ahead and start containers named $name,
which will then race to set up the lxc control socket, which is named
after the container name and the rootfs path, which are both the same
here.

The fix is to add some randomness to the lxc container name, which
ensures that the socket won't clash. This should not affect other uses
of the image name, which will still use the un-randomized name.

Signed-off-by: Michael McCracken <[email protected]>

pkg/container/container.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"syscall"
 
+	"github.com/google/uuid"
 	"github.com/lxc/go-lxc"
 	"github.com/pkg/errors"
 	embed_exec "stackerbuild.io/stacker/pkg/embed-exec"
@@ -36,7 +37,8 @@ func New(sc types.StackerConfig, name string) (*Container, error) {
 		return nil, errors.WithStack(err)
 	}
 
-	lxcC, err := lxc.NewContainer(name, sc.RootFSDir)
+	uniqname := fmt.Sprintf("%s-%s", name, uuid.NewString())
+	lxcC, err := lxc.NewContainer(uniqname, sc.RootFSDir)
 	if err != nil {
 		return nil, err
 	}

test/concurrent.bats

@@ -0,0 +1,37 @@
+load helpers
+
+function setup() {
+    stacker_setup
+}
+
+function teardown() {
+    cleanup
+}
+
+@test "concurrent w aliased rootdir" {
+    cat > stacker.yaml <<"EOF"
+robertos:
+    from:
+        type: oci
+        url: ${{BUSYBOX_OCI}}
+    run: |
+      sleep ${{SNOOZ}} # make sure they have time to conflict
+EOF
+
+    mkdir -p 1/roots 1/stacker 2/roots 2/stacker aliased-rootsdir
+    chmod -R 777 1 2
+
+    # simulate shared CI infra where name of sandbox dir is same despite backing store being different
+
+    mount --bind 1/roots aliased-rootsdir
+    ${ROOT_DIR}/stacker --debug --roots-dir=aliased-rootsdir --stacker-dir=1/stacker --oci-dir=1/oci --log-file=1.log build --substitute BUSYBOX_OCI=${BUSYBOX_OCI} --substitute SNOOZ=15 &
+
+    sleep 5
+
+    unshare -m bash <<EOF
+        mount --bind 2/roots aliased-rootsdir
+        ${ROOT_DIR}/stacker --debug --roots-dir=aliased-rootsdir --stacker-dir=2/stacker --oci-dir=2/oci --log-file=2.log \
+            build --substitute BUSYBOX_OCI=${BUSYBOX_OCI} --substitute SNOOZ=0
+EOF
+
+}