Allow additional groups to be overridden in exec

Signed-off-by: Julian Friedman <julz.friedman@uk.ibm.com>
Signed-off-by: Petar Petrov <pppepito86@gmail.com>
Signed-off-by: Georgi Sabev <georgethebeatle@gmail.com>

utils_linux.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strconv"
 	"syscall"
 
 	"github.com/Sirupsen/logrus"
@@ -83,6 +84,9 @@ func newProcess(p specs.Process) (*libcontainer.Process, error) {
 		NoNewPrivileges: &p.NoNewPrivileges,
 		AppArmorProfile: p.ApparmorProfile,
 	}
+	for _, gid := range p.User.AdditionalGids {
+		lp.AdditionalGroups = append(lp.AdditionalGroups, strconv.FormatUint(uint64(gid), 10))
+	}
 	for _, rlimit := range p.Rlimits {
 		rl, err := createLibContainerRlimit(rlimit)
 		if err != nil {