rootlessport: set source IP to slirp4netns device

set the source IP to the slirp4netns address instead of 127.0.0.1 when
using rootlesskit.

Closes: https://github.com/containers/podman/issues/5138

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

libpod/networking_linux.go

@@ -547,6 +547,7 @@ func (r *Runtime) setupRootlessPortMappingViaRLK(ctr *Container, netnsPath strin
 		ExitFD:    3,
 		ReadyFD:   4,
 		TmpDir:    ctr.runtime.config.Engine.TmpDir,
+		ChildIP:   "10.0.2.100",
 	}
 	cfgJSON, err := json.Marshal(cfg)
 	if err != nil {

pkg/rootlessport/rootlessport_linux.go

@@ -48,6 +48,7 @@ type Config struct {
 	ExitFD    int
 	ReadyFD   int
 	TmpDir    string
+	ChildIP   string
 }
 
 func init() {
@@ -227,7 +228,7 @@ outer:
 
 	// let parent expose ports
 	logrus.Infof("exposing ports %v", cfg.Mappings)
-	if err := exposePorts(driver, cfg.Mappings); err != nil {
+	if err := exposePorts(driver, cfg.Mappings, cfg.ChildIP); err != nil {
 		return err
 	}
 
@@ -248,7 +249,7 @@ outer:
 	return nil
 }
 
-func exposePorts(pm rkport.Manager, portMappings []ocicni.PortMapping) error {
+func exposePorts(pm rkport.Manager, portMappings []ocicni.PortMapping, childIP string) error {
 	ctx := context.TODO()
 	for _, i := range portMappings {
 		hostIP := i.HostIP
@@ -260,6 +261,7 @@ func exposePorts(pm rkport.Manager, portMappings []ocicni.PortMapping) error {
 			ParentIP:   hostIP,
 			ParentPort: int(i.HostPort),
 			ChildPort:  int(i.ContainerPort),
+			ChildIP:    childIP,
 		}
 		if err := rkportutil.ValidatePortSpec(spec, nil); err != nil {
 			return err

test/system/500-networking.bats

@@ -65,8 +65,13 @@ load helpers
     myport=54321
 
     # Container will exit as soon as 'nc' receives input
+    # We use '-n -v' to give us log messages showing an incoming connection
+    # and its IP address; the purpose of that is guaranteeing that the
+    # remote IP is not 127.0.0.1 (podman PR #9052).
+    # We could get more parseable output by using $NCAT_REMOTE_ADDR,
+    # but busybox nc doesn't support that.
     run_podman run -d --userns=keep-id -p 127.0.0.1:$myport:$myport \
-               $IMAGE nc -l -p $myport
+               $IMAGE nc -l -n -v -p $myport
     cid="$output"
 
     # emit random string, and check it
@@ -74,7 +79,17 @@ load helpers
     echo "$teststring" | nc 127.0.0.1 $myport
 
     run_podman logs $cid
-    is "$output" "$teststring" "test string received on container"
+    # Sigh. We can't check line-by-line, because 'nc' output order is
+    # unreliable. We usually get the 'connect to' line before the random
+    # string, but sometimes we get it after. So, just do substring checks.
+    is "$output" ".*listening on \[::\]:$myport .*" "nc -v shows right port"
+
+    # This is the truly important check: make sure the remote IP is
+    # in the 10.X range, not 127.X.
+    is "$output" \
+       ".*connect to \[::ffff:10\..*\]:$myport from \[::ffff:10\..*\]:.*" \
+       "nc -v shows remote IP address in 10.X space (not 127.0.0.1)"
+    is "$output" ".*${teststring}.*" "test string received on container"
 
     # Clean up
     run_podman rm $cid