libpod: bind ports before network setup

We bind ports to ensure there are no conflicts and we leak them into
conmon to keep them open. However we bound the ports after the network
was set up so it was possible for a second network setup to overwrite
the firewall configs of a previous container as it failed only later
when binding the port. As such we must ensure we bind before the network
is set up.

This is not so simple because we still have to take care of
PostConfigureNetNS bool in which case the network set up happens after
we launch conmon. Thus we end up with two different conditions.

Also it is possible that we "leak" the ports that are set on the
container until the garbage collector will close them. This is not
perfect but the alternative is adding special error handling on each
function exit after prepare until we start conmon which is a lot of work
to do correctly.

Fixes https://issues.redhat.com/browse/RHEL-50746

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/container.go

@@ -118,6 +118,10 @@ type Container struct {
 	rootlessPortSyncR *os.File
 	rootlessPortSyncW *os.File
 
+	// reservedPorts contains the fds for the bound ports when using the
+	// bridge network mode as root.
+	reservedPorts []*os.File
+
 	// perNetworkOpts should be set when you want to use special network
 	// options when calling network setup/teardown. This should be used for
 	// container restore or network reload for example. Leave this nil if

libpod/container_internal_freebsd.go

@@ -50,6 +50,10 @@ func (c *Container) prepare() error {
 		// Set up network namespace if not already set up
 		noNetNS := c.state.NetNS == ""
 		if c.config.CreateNetNS && noNetNS && !c.config.PostConfigureNetNS {
+			c.reservedPorts, createNetNSErr = c.bindPorts()
+			if createNetNSErr != nil {
+				return
+			}
 			ctrNS, networkStatus, createNetNSErr = c.runtime.createNetNS(c)
 			if createNetNSErr != nil {
 				return
@@ -112,6 +116,11 @@ func (c *Container) prepare() error {
 			logrus.Errorf("Preparing container %s: %v", c.ID(), createErr)
 			createErr = fmt.Errorf("cleaning up container %s network after setup failure: %w", c.ID(), err)
 		}
+		for _, f := range c.reservedPorts {
+			// make sure to close all ports again on errors
+			f.Close()
+		}
+		c.reservedPorts = nil
 		return createErr
 	}
 

libpod/container_internal_linux.go

@@ -82,6 +82,11 @@ func (c *Container) prepare() error {
 		// Set up network namespace if not already set up
 		noNetNS := c.state.NetNS == ""
 		if c.config.CreateNetNS && noNetNS && !c.config.PostConfigureNetNS {
+			c.reservedPorts, createNetNSErr = c.bindPorts()
+			if createNetNSErr != nil {
+				return
+			}
+
 			netNS, networkStatus, createNetNSErr = c.runtime.createNetNS(c)
 			if createNetNSErr != nil {
 				return
@@ -148,6 +153,11 @@ func (c *Container) prepare() error {
 	}
 
 	if createErr != nil {
+		for _, f := range c.reservedPorts {
+			// make sure to close all ports again on errors
+			f.Close()
+		}
+		c.reservedPorts = nil
 		return createErr
 	}
 

libpod/networking_common.go

@@ -5,6 +5,7 @@ package libpod
 import (
 	"errors"
 	"fmt"
+	"os"
 	"regexp"
 	"slices"
 	"sort"
@@ -21,6 +22,16 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
+// bindPorts ports to keep them open via conmon so no other process can use them and we can check if they are in use.
+// Note in all cases it is important that we bind before setting up the network to avoid issues were we add firewall
+// rules before we even "own" the port.
+func (c *Container) bindPorts() ([]*os.File, error) {
+	if !c.runtime.config.Engine.EnablePortReservation || rootless.IsRootless() || !c.config.NetMode.IsBridge() {
+		return nil, nil
+	}
+	return bindPorts(c.convertPortMappings())
+}
+
 // convertPortMappings will remove the HostIP part from the ports when running inside podman machine.
 // This is needed because a HostIP of 127.0.0.1 would now allow the gvproxy forwarder to reach to open ports.
 // For machine the HostIP must only be used by gvproxy and never in the VM.

libpod/oci_conmon_common.go

@@ -1216,17 +1216,22 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 	cmd.Env = append(cmd.Env, conmonEnv...)
 	cmd.ExtraFiles = append(cmd.ExtraFiles, childSyncPipe, childStartPipe)
 
-	if r.reservePorts && !rootless.IsRootless() && !ctr.config.NetMode.IsSlirp4netns() {
+	if ctr.config.PostConfigureNetNS {
-		ports, err := bindPorts(ctr.convertPortMappings())
+		// netns was not setup yet but we have to bind ports now so we can leak the fd to conmon
+		ports, err := ctr.bindPorts()
 		if err != nil {
 			return 0, err
 		}
 		filesToClose = append(filesToClose, ports...)
-
 		// Leak the port we bound in the conmon process.  These fd's won't be used
 		// by the container and conmon will keep the ports busy so that another
 		// process cannot use them.
 		cmd.ExtraFiles = append(cmd.ExtraFiles, ports...)
+	} else {
+		// ports were bound in ctr.prepare() as we must do it before the netns setup
+		filesToClose = append(filesToClose, ctr.reservedPorts...)
+		cmd.ExtraFiles = append(cmd.ExtraFiles, ctr.reservedPorts...)
+		ctr.reservedPorts = nil
 	}
 
 	if ctr.config.NetMode.IsSlirp4netns() || rootless.IsRootless() {

libpod/oci_util.go

@@ -46,7 +46,12 @@ func bindPorts(ports []types.PortMapping) ([]*os.File, error) {
 			for i := uint16(0); i < port.Range; i++ {
 				f, err := bindPort(protocol, port.HostIP, port.HostPort+i, isV6, &sctpWarning)
 				if err != nil {
-					return files, err
+					// close all open ports in case of early error so we do not
+					// rely garbage  collector to close them
+					for _, f := range files {
+						f.Close()
+					}
+					return nil, err
 				}
 				if f != nil {
 					files = append(files, f)

test/system/500-networking.bats

@@ -54,6 +54,15 @@ load helpers.network
             $IMAGE /bin/busybox-extras httpd -f -p 80
     cid=$output
 
+    # Try to bind the same port again, this must fail.
+    # regression test for https://issues.redhat.com/browse/RHEL-50746
+    # which caused this command to overwrite the firewall rules as root
+    # causing the curl commands below to fail
+    run_podman 126 run --rm -p "$HOST_PORT:80" $IMAGE true
+    # Note error messages differ between root/rootless, so only check port
+    # and the part of the error text that is common.
+    assert "$output" =~ "$HOST_PORT.*ddress already in use" "port in use"
+
     # In that container, create a second file, using exec and redirection
     run_podman exec -i myweb sh -c "cat > index2.txt" <<<"$random_2"
     # ...verify its contents as seen from container.
@@ -61,9 +70,9 @@ load helpers.network
     is "$output" "$random_2" "exec cat index2.txt"
 
     # Verify http contents: curl from localhost
-    run curl -s -S $SERVER/index.txt
+    run curl --max-time 3 -s -S $SERVER/index.txt
     is "$output" "$random_1" "curl 127.0.0.1:/index.txt"
-    run curl -s -S $SERVER/index2.txt
+    run curl --max-time 3 -s -S $SERVER/index2.txt
     is "$output" "$random_2" "curl 127.0.0.1:/index2.txt"
 
     # Verify http contents: wget from a second container