Patch upstream issue where multus delegates to itself

and breaks pod networking by try multiple times to create the same interface.

Issue fixed: rancher/rke2#4568

Dockerfile

@@ -11,10 +11,14 @@ ARG ARCH
 ARG TAG
 ENV GOARCH ${ARCH}
 ENV GOOS "linux"
+# patch to solve https://github.com/rancher/rke2/issues/4568
+# to be removed once upstream merges the fix
+COPY self_delegation_bug.patch /tmp
 RUN git clone --depth=1 https://github.com/k8snetworkplumbingwg/multus-cni && \
     cd multus-cni && \
     git fetch --all --tags --prune && \
     git checkout tags/${TAG} -b ${TAG} && \
+    git apply /tmp/self_delegation_bug.patch && \
     ./hack/build-go.sh
 
 # Create the multus image

self_delegation_bug.patch

@@ -0,0 +1,36 @@
+diff --git a/cmd/thin_entrypoint/main.go b/cmd/thin_entrypoint/main.go
+index ac721518..3f0e835f 100644
+--- a/cmd/thin_entrypoint/main.go
++++ b/cmd/thin_entrypoint/main.go
+@@ -23,7 +23,9 @@ import (
+ 	"fmt"
+ 	"io"
+ 	"os"
++	"path"
+ 	"path/filepath"
++	"regexp"
+ 	"strings"
+ 	"text/template"
+ 	"time"
+@@ -294,7 +296,20 @@ func (o *Options) createMultusConfig() (string, error) {
+ 		return "", fmt.Errorf("cannot find master CNI config in %q: %v", o.MultusAutoconfigDir, err)
+ 	}
+
+-	masterConfigPath := files[0]
++	var masterConfigPath string
++	// skip existing multus configuration file to avoid creating a situation
++	// where multus delegates to itself and breaks pod networking
++	multusRegexp, err := regexp.Compile("multus")
++	if err != nil {
++		return "", fmt.Errorf("regexp compilation failed: %v", err)
++	}
++	for _, filename := range files {
++		if !multusRegexp.MatchString(path.Base(filename)) {
++			masterConfigPath = filename
++			break
++		}
++	}
++
+ 	masterConfigBytes, err := os.ReadFile(masterConfigPath)
+ 	if err != nil {
+ 		return "", fmt.Errorf("cannot read master CNI config file %q: %v", masterConfigPath, err)