Add support for --pid=container:<id>

Signed-off-by: Mrunal Patel <mrunalp@gmail.com>

contrib/completion/bash/docker

@@ -1832,6 +1832,21 @@ _docker_run() {
 			esac
 			return
 			;;
+		--pid)
+			case "$cur" in
+				*:*)
+					cur="${cur#*:}"
+					__docker_complete_containers_running
+					;;
+				*)
+					COMPREPLY=( $( compgen -W 'host container:' -- "$cur" ) )
+					if [ "$COMPREPLY" = "container:" ]; then
+						__docker_nospace
+					fi
+					;;
+			esac
+			return
+			;;
 		--security-opt)
 			COMPREPLY=( $( compgen -W "apparmor= label= no-new-privileges seccomp=" -- "$cur") )
 			if [ "${COMPREPLY[*]}" != "no-new-privileges" ] ; then

contrib/completion/zsh/_docker

@@ -699,7 +699,7 @@ __docker_subcommand() {
         "($help)--pids-limit[Tune container pids limit (set -1 for unlimited)]"
         "($help -P --publish-all)"{-P,--publish-all}"[Publish all exposed ports]"
         "($help)*"{-p=,--publish=}"[Expose a container's port to the host]:port:_ports"
-        "($help)--pid=[PID namespace to use]:PID: "
+        "($help)--pid=[PID namespace to use]:PID namespace: "
         "($help)--privileged[Give extended privileges to this container]"
         "($help)--read-only[Mount the container's root filesystem as read only]"
         "($help)*--security-opt=[Security options]:security option: "

daemon/container_operations_unix.go

@@ -169,6 +169,21 @@ func (daemon *Daemon) getIpcContainer(container *container.Container) (*containe
 	return c, nil
 }
 
+func (daemon *Daemon) getPidContainer(container *container.Container) (*container.Container, error) {
+	containerID := container.HostConfig.PidMode.Container()
+	c, err := daemon.GetContainer(containerID)
+	if err != nil {
+		return nil, err
+	}
+	if !c.IsRunning() {
+		return nil, fmt.Errorf("cannot join PID of a non running container: %s", containerID)
+	}
+	if c.IsRestarting() {
+		return nil, errContainerIsRestarting(container.ID)
+	}
+	return c, nil
+}
+
 func (daemon *Daemon) setupIpcDirs(c *container.Container) error {
 	var err error
 

daemon/create.go

@@ -142,13 +142,40 @@ func (daemon *Daemon) generateSecurityOpt(ipcMode containertypes.IpcMode, pidMod
 	if ipcMode.IsHost() || pidMode.IsHost() {
 		return label.DisableSecOpt(), nil
 	}
-	if ipcContainer := ipcMode.Container(); ipcContainer != "" {
+
+	var ipcLabel []string
+	var pidLabel []string
+	ipcContainer := ipcMode.Container()
+	pidContainer := pidMode.Container()
+	if ipcContainer != "" {
 		c, err := daemon.GetContainer(ipcContainer)
 		if err != nil {
 			return nil, err
 		}
+		ipcLabel = label.DupSecOpt(c.ProcessLabel)
+		if pidContainer == "" {
+			return ipcLabel, err
+		}
+	}
+	if pidContainer != "" {
+		c, err := daemon.GetContainer(pidContainer)
+		if err != nil {
+			return nil, err
+		}
 
-		return label.DupSecOpt(c.ProcessLabel), nil
+		pidLabel = label.DupSecOpt(c.ProcessLabel)
+		if ipcContainer == "" {
+			return pidLabel, err
+		}
+	}
+
+	if pidLabel != nil && ipcLabel != nil {
+		for i := 0; i < len(pidLabel); i++ {
+			if pidLabel[i] != ipcLabel[i] {
+				return nil, fmt.Errorf("--ipc and --pid containers SELinux labels aren't the same")
+			}
+		}
+		return pidLabel, nil
 	}
 	return nil, nil
 }

daemon/oci_linux.go

@@ -296,8 +296,25 @@ func setNamespaces(daemon *Daemon, s *specs.Spec, c *container.Container) error
 		setNamespace(s, ns)
 	}
 	// pid
-	if c.HostConfig.PidMode.IsHost() {
+	if c.HostConfig.PidMode.IsContainer() {
+		ns := specs.Namespace{Type: "pid"}
+		pc, err := daemon.getPidContainer(c)
+		if err != nil {
+			return err
+		}
+		ns.Path = fmt.Sprintf("/proc/%d/ns/pid", pc.State.GetPID())
+		setNamespace(s, ns)
+		if userNS {
+			// to share an PID namespace, they must also share a user namespace
+			nsUser := specs.Namespace{Type: "user"}
+			nsUser.Path = fmt.Sprintf("/proc/%d/ns/user", pc.State.GetPID())
+			setNamespace(s, nsUser)
+		}
+	} else if c.HostConfig.PidMode.IsHost() {
 		delNamespace(s, specs.NamespaceType("pid"))
+	} else {
+		ns := specs.Namespace{Type: "pid"}
+		setNamespace(s, ns)
 	}
 	// uts
 	if c.HostConfig.UTSMode.IsHost() {

docs/reference/run.md

@@ -193,7 +193,8 @@ the digest value is predictable and referenceable.
 ## PID settings (--pid)
 
     --pid=""  : Set the PID (Process) Namespace mode for the container,
-           'host': use the host's PID namespace inside the container
+                 'container:<name|id>': joins another container's PID namespace
+                 'host': use the host's PID namespace inside the container
 
 By default, all containers have the PID namespace enabled.
 
@@ -229,6 +230,23 @@ Use the following command to run `htop` inside a container:
 $ docker run -it --rm --pid=host myhtop
 ```
 
+Joining another container's pid namespace can be used for debugging that container.
+
+### Example
+
+Start a container running a redis server:
+
+```bash
+$ docker run --name my-redis -d redis
+```
+
+Debug the redis container by running another container that has strace in it:
+
+```bash
+$ docker run --it --pid=container:my-redis bash
+$ strace -p 1
+```
+
 ## UTS settings (--uts)
 
     --uts=""  : Set the UTS namespace mode for the container,

integration-cli/docker_cli_run_test.go

@@ -2443,6 +2443,53 @@ func (s *DockerSuite) TestRunModeIpcContainerNotRunning(c *check.C) {
 	}
 }
 
+func (s *DockerSuite) TestRunModePidContainer(c *check.C) {
+	// Not applicable on Windows as uses Unix-specific capabilities
+	testRequires(c, SameHostDaemon, DaemonIsLinux)
+
+	out, _ := dockerCmd(c, "run", "-d", "busybox", "sh", "-c", "top")
+
+	id := strings.TrimSpace(out)
+	state := inspectField(c, id, "State.Running")
+	if state != "true" {
+		c.Fatal("Container state is 'not running'")
+	}
+	pid1 := inspectField(c, id, "State.Pid")
+
+	parentContainerPid, err := os.Readlink(fmt.Sprintf("/proc/%s/ns/pid", pid1))
+	if err != nil {
+		c.Fatal(err)
+	}
+
+	out, _ = dockerCmd(c, "run", fmt.Sprintf("--pid=container:%s", id), "busybox", "readlink", "/proc/self/ns/pid")
+	out = strings.Trim(out, "\n")
+	if parentContainerPid != out {
+		c.Fatalf("PID different with --pid=container:%s %s != %s\n", id, parentContainerPid, out)
+	}
+}
+
+func (s *DockerSuite) TestRunModePidContainerNotExists(c *check.C) {
+	// Not applicable on Windows as uses Unix-specific capabilities
+	testRequires(c, DaemonIsLinux)
+	out, _, err := dockerCmdWithError("run", "-d", "--pid", "container:abcd1234", "busybox", "top")
+	if !strings.Contains(out, "abcd1234") || err == nil {
+		c.Fatalf("run PID from a non exists container should with correct error out")
+	}
+}
+
+func (s *DockerSuite) TestRunModePidContainerNotRunning(c *check.C) {
+	// Not applicable on Windows as uses Unix-specific capabilities
+	testRequires(c, SameHostDaemon, DaemonIsLinux)
+
+	out, _ := dockerCmd(c, "create", "busybox")
+
+	id := strings.TrimSpace(out)
+	out, _, err := dockerCmdWithError("run", fmt.Sprintf("--pid=container:%s", id), "busybox")
+	if err == nil {
+		c.Fatalf("Run container with pid mode container should fail with non running container: %s\n%s", out, err)
+	}
+}
+
 func (s *DockerSuite) TestRunMountShmMqueueFromHost(c *check.C) {
 	// Not applicable on Windows as uses Unix-specific capabilities
 	testRequires(c, SameHostDaemon, DaemonIsLinux, NotUserNamespace)

man/docker-create.1.md

@@ -57,7 +57,7 @@ docker-create - Create a new container
 [**--oom-score-adj**[=*0*]]
 [**-P**|**--publish-all**]
 [**-p**|**--publish**[=*[]*]]
-[**--pid**[=*[]*]]
+[**--pid**[=*[PID]*]]
 [**--userns**[=*[]*]]
 [**--pids-limit**[=*PIDS_LIMIT*]]
 [**--privileged**]
@@ -289,10 +289,11 @@ unit, `b` is used. Set LIMIT to `-1` to enable unlimited swap.
                                When specifying ranges for both, the number of container ports in the range must match the number of host ports in the range. (e.g., `-p 1234-1236:1234-1236/tcp`)
                                (use 'docker port' to see the actual mapping)
 
-**--pid**=*host*
+**--pid**=""
    Set the PID mode for the container
-     **host**: use the host's PID namespace inside the container.
-     Note: the host mode gives the container full access to local PID and is therefore considered insecure.
+   Default is to create a private PID namespace for the container
+                               'container:<name|id>': join another container's PID namespace
+                               'host': use the host's PID namespace for the container. Note: the host mode gives the container full access to local PID and is therefore considered insecure.
 
 **--userns**=""
    Set the usernamespace mode for the container when `userns-remap` option is enabled.

man/docker-run.1.md

@@ -59,7 +59,7 @@ docker-run - Run a command in a new container
 [**--oom-score-adj**[=*0*]]
 [**-P**|**--publish-all**]
 [**-p**|**--publish**[=*[]*]]
-[**--pid**[=*[]*]]
+[**--pid**[=*[PID]*]]
 [**--userns**[=*[]*]]
 [**--pids-limit**[=*PIDS_LIMIT*]]
 [**--privileged**]
@@ -420,10 +420,11 @@ but not `docker run -p 1230-1236:1230-1240 --name RangeContainerPortsBiggerThanR
 With ip: `docker run -p 127.0.0.1:$HOSTPORT:$CONTAINERPORT --name CONTAINER -t someimage`
 Use `docker port` to see the actual mapping: `docker port CONTAINER $CONTAINERPORT`
 
-**--pid**=*host*
+**--pid**=""
    Set the PID mode for the container
-     **host**: use the host's PID namespace inside the container.
-     Note: the host mode gives the container full access to local PID and is therefore considered insecure.
+   Default is to create a private PID namespace for the container
+                               'container:<name|id>': join another container's PID namespace
+                               'host': use the host's PID namespace for the container. Note: the host mode gives the container full access to local PID and is therefore considered insecure.
 
 **--userns**=""
    Set the usernamespace mode for the container when `userns-remap` option is enabled.