[docker compat] Don't overwrite the NetworkMode from "default" to "bridge" if containers.conf specifies a non-default configuration.

pkg/api/handlers/compat/containers_create.go

@@ -262,10 +262,17 @@ func cliOpts(cc handlers.CreateContainerConfig, rtc *config.Config) (*entities.C
 	}
 
 	// special case for NetworkMode, the podman default is slirp4netns for
-	// rootless but for better docker compat we want bridge.
+	// rootless but for better docker compat we want bridge. Do this only if
+	// the default config in containers.conf wasn't overridden to use another
+	// value than the default "private" one.
 	netmode := string(cc.HostConfig.NetworkMode)
+	configDefaultNetNS := rtc.Containers.NetNS
 	if netmode == "" || netmode == "default" {
-		netmode = "bridge"
+		if configDefaultNetNS == "" || configDefaultNetNS == string(specgen.Default) || configDefaultNetNS == string(specgen.Private) {
+			netmode = "bridge"
+		} else {
+			netmode = configDefaultNetNS
+		}
 	}
 
 	nsmode, networks, netOpts, err := specgen.ParseNetworkFlag([]string{netmode}, false)

test/apiv2/20-containers.at

@@ -417,6 +417,24 @@ t GET containers/$cid/json 200 \
 
 t DELETE containers/$cid?v=true 204
 
+# test create with default netns="host"
+stop_service
+CONTAINERS_CONF=$TESTS_DIR/containers.host-netns.conf start_service
+
+# check that the default docker netns "default" is rewritten to "host"
+# when the containers.conf explicitly uses "host"
+t POST containers/create Image=$IMAGE HostConfig='{"NetworkMode":"default"}' 201 \
+  .Id~[0-9a-f]\\{64\\}
+cid=$(jq -r '.Id' <<<"$output")
+t GET containers/$cid/json 200 \
+  .HostConfig.NetworkMode="host"
+
+t DELETE containers/$cid?v=true 204
+
+# Restart with the default containers.conf for next tests.
+stop_service
+start_service
+
 # Test Compat Create with healthcheck, check default values
 t POST containers/create Image=$IMAGE Cmd='["top"]' Healthcheck='{"Test":["true"]}' 201 \
   .Id~[0-9a-f]\\{64\\}

test/apiv2/containers.host-netns.conf

@@ -0,0 +1,2 @@
+[containers]
+netns="host"