Clear all caps, except the bounding set, when --user is specified.

Currently we are giving all caps to users when running with podman run --user,
They should get none by default.  If the command line includes --cap-add, then
we need to run with those capabilties.  Similarly we need to drop caps from
bounding set, if user specifies --cap-drop

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #851
Approved by: mheon

pkg/spec/spec.go

@@ -388,8 +388,19 @@ func addRlimits(config *CreateConfig, g *generate.Generator) error {
 }
 
 func setupCapabilities(config *CreateConfig, configSpec *spec.Spec) error {
+	useNotRoot := func(user string) bool {
+		if user == "" || user == "root" || user == "0" {
+			return false
+		}
+		return true
+	}
+
 	var err error
 	var caplist []string
+	bounding := configSpec.Process.Capabilities.Bounding
+	if useNotRoot(config.User) {
+		configSpec.Process.Capabilities.Bounding = caplist
+	}
 	caplist, err = caps.TweakCapabilities(configSpec.Process.Capabilities.Bounding, config.CapAdd, config.CapDrop)
 	if err != nil {
 		return err
@@ -399,6 +410,14 @@ func setupCapabilities(config *CreateConfig, configSpec *spec.Spec) error {
 	configSpec.Process.Capabilities.Permitted = caplist
 	configSpec.Process.Capabilities.Inheritable = caplist
 	configSpec.Process.Capabilities.Effective = caplist
+	configSpec.Process.Capabilities.Ambient = caplist
+	if useNotRoot(config.User) {
+		caplist, err = caps.TweakCapabilities(bounding, config.CapAdd, config.CapDrop)
+		if err != nil {
+			return err
+		}
+	}
+	configSpec.Process.Capabilities.Bounding = caplist
 	return nil
 }
 

test/e2e/run_test.go

@@ -5,6 +5,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/mrunalp/fileutils"
 	. "github.com/onsi/ginkgo"
@@ -369,6 +370,14 @@ var _ = Describe("Podman run", func() {
 		Expect(session.OutputToString()).To(Equal("uid=8(mail) gid=21(ftp)"))
 	})
 
+	It("podman run with user, verify caps dropped", func() {
+		session := podmanTest.Podman([]string{"run", "--rm", "--user=1234", ALPINE, "grep", "CapEff", "/proc/self/status"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+		capEff := strings.Split(session.OutputToString(), " ")
+		Expect("0000000000000000").To(Equal(capEff[1]))
+	})
+
 	It("podman run with attach stdin outputs container ID", func() {
 		session := podmanTest.Podman([]string{"run", "--attach", "stdin", ALPINE, "printenv"})
 		session.WaitWithDefaultTimeout()