Add cap-add and cap-drop to build man page

Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>

Closes: #968
Approved by: mheon

vendor/github.com/projectatomic/buildah/util/util.go

@@ -1,11 +1,13 @@
 package util
 
 import (
+	"bufio"
 	"fmt"
 	"io"
 	"net/url"
 	"os"
 	"path"
+	"strconv"
 	"strings"
 
 	"github.com/containers/image/directory"
@@ -17,7 +19,9 @@ import (
 	"github.com/containers/image/tarball"
 	"github.com/containers/image/types"
 	"github.com/containers/storage"
+	"github.com/containers/storage/pkg/idtools"
 	"github.com/docker/distribution/registry/api/errcode"
+	"github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -243,3 +247,184 @@ func Runtime() string {
 	}
 	return DefaultRuntime
 }
+
+// StringInSlice returns a boolean indicating if the exact value s is present
+// in the slice slice.
+func StringInSlice(s string, slice []string) bool {
+	for _, v := range slice {
+		if v == s {
+			return true
+		}
+	}
+	return false
+}
+
+// GetHostIDs uses ID mappings to compute the host-level IDs that will
+// correspond to a UID/GID pair in the container.
+func GetHostIDs(uidmap, gidmap []specs.LinuxIDMapping, uid, gid uint32) (uint32, uint32, error) {
+	uidMapped := true
+	for _, m := range uidmap {
+		uidMapped = false
+		if uid >= m.ContainerID && uid < m.ContainerID+m.Size {
+			uid = (uid - m.ContainerID) + m.HostID
+			uidMapped = true
+			break
+		}
+	}
+	if !uidMapped {
+		return 0, 0, errors.Errorf("container uses ID mappings, but doesn't map UID %d", uid)
+	}
+	gidMapped := true
+	for _, m := range gidmap {
+		gidMapped = false
+		if gid >= m.ContainerID && gid < m.ContainerID+m.Size {
+			gid = (gid - m.ContainerID) + m.HostID
+			gidMapped = true
+			break
+		}
+	}
+	if !gidMapped {
+		return 0, 0, errors.Errorf("container uses ID mappings, but doesn't map GID %d", gid)
+	}
+	return uid, gid, nil
+}
+
+// GetHostRootIDs uses ID mappings in spec to compute the host-level IDs that will
+// correspond to UID/GID 0/0 in the container.
+func GetHostRootIDs(spec *specs.Spec) (uint32, uint32, error) {
+	if spec.Linux == nil {
+		return 0, 0, nil
+	}
+	return GetHostIDs(spec.Linux.UIDMappings, spec.Linux.GIDMappings, 0, 0)
+}
+
+// getHostIDMappings reads mappings from the named node under /proc.
+func getHostIDMappings(path string) ([]specs.LinuxIDMapping, error) {
+	var mappings []specs.LinuxIDMapping
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, errors.Wrapf(err, "error reading ID mappings from %q", path)
+	}
+	defer f.Close()
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+		fields := strings.Fields(line)
+		if len(fields) != 3 {
+			return nil, errors.Errorf("line %q from %q has %d fields, not 3", line, path, len(fields))
+		}
+		cid, err := strconv.ParseUint(fields[0], 10, 32)
+		if err != nil {
+			return nil, errors.Wrapf(err, "error parsing container ID value %q from line %q in %q", fields[0], line, path)
+		}
+		hid, err := strconv.ParseUint(fields[1], 10, 32)
+		if err != nil {
+			return nil, errors.Wrapf(err, "error parsing host ID value %q from line %q in %q", fields[1], line, path)
+		}
+		size, err := strconv.ParseUint(fields[2], 10, 32)
+		if err != nil {
+			return nil, errors.Wrapf(err, "error parsing size value %q from line %q in %q", fields[2], line, path)
+		}
+		mappings = append(mappings, specs.LinuxIDMapping{ContainerID: uint32(cid), HostID: uint32(hid), Size: uint32(size)})
+	}
+	return mappings, nil
+}
+
+// GetHostIDMappings reads mappings for the current process from the kernel.
+func GetHostIDMappings(pid string) ([]specs.LinuxIDMapping, []specs.LinuxIDMapping, error) {
+	if pid == "" {
+		pid = "self"
+	}
+	uidmap, err := getHostIDMappings(fmt.Sprintf("/proc/%s/uid_map", pid))
+	if err != nil {
+		return nil, nil, err
+	}
+	gidmap, err := getHostIDMappings(fmt.Sprintf("/proc/%s/gid_map", pid))
+	if err != nil {
+		return nil, nil, err
+	}
+	return uidmap, gidmap, nil
+}
+
+// GetSubIDMappings reads mappings from /etc/subuid and /etc/subgid.
+func GetSubIDMappings(user, group string) ([]specs.LinuxIDMapping, []specs.LinuxIDMapping, error) {
+	mappings, err := idtools.NewIDMappings(user, group)
+	if err != nil {
+		return nil, nil, errors.Wrapf(err, "error reading subuid mappings for user %q and subgid mappings for group %q", user, group)
+	}
+	var uidmap, gidmap []specs.LinuxIDMapping
+	for _, m := range mappings.UIDs() {
+		uidmap = append(uidmap, specs.LinuxIDMapping{
+			ContainerID: uint32(m.ContainerID),
+			HostID:      uint32(m.HostID),
+			Size:        uint32(m.Size),
+		})
+	}
+	for _, m := range mappings.GIDs() {
+		gidmap = append(gidmap, specs.LinuxIDMapping{
+			ContainerID: uint32(m.ContainerID),
+			HostID:      uint32(m.HostID),
+			Size:        uint32(m.Size),
+		})
+	}
+	return uidmap, gidmap, nil
+}
+
+// ParseIDMappings parses mapping triples.
+func ParseIDMappings(uidmap, gidmap []string) ([]idtools.IDMap, []idtools.IDMap, error) {
+	nonDigitsToWhitespace := func(r rune) rune {
+		if strings.IndexRune("0123456789", r) == -1 {
+			return ' '
+		} else {
+			return r
+		}
+	}
+	parseTriple := func(spec []string) (container, host, size uint32, err error) {
+		cid, err := strconv.ParseUint(spec[0], 10, 32)
+		if err != nil {
+			return 0, 0, 0, fmt.Errorf("error parsing id map value %q: %v", spec[0], err)
+		}
+		hid, err := strconv.ParseUint(spec[1], 10, 32)
+		if err != nil {
+			return 0, 0, 0, fmt.Errorf("error parsing id map value %q: %v", spec[1], err)
+		}
+		sz, err := strconv.ParseUint(spec[2], 10, 32)
+		if err != nil {
+			return 0, 0, 0, fmt.Errorf("error parsing id map value %q: %v", spec[2], err)
+		}
+		return uint32(cid), uint32(hid), uint32(sz), nil
+	}
+	parseIDMap := func(mapSpec []string, mapSetting string) (idmap []idtools.IDMap, err error) {
+		for _, idMapSpec := range mapSpec {
+			idSpec := strings.Fields(strings.Map(nonDigitsToWhitespace, idMapSpec))
+			if len(idSpec)%3 != 0 {
+				return nil, errors.Errorf("error initializing ID mappings: %s setting is malformed", mapSetting)
+			}
+			for i := range idSpec {
+				if i%3 != 0 {
+					continue
+				}
+				cid, hid, size, err := parseTriple(idSpec[i : i+3])
+				if err != nil {
+					return nil, errors.Errorf("error initializing ID mappings: %s setting is malformed", mapSetting)
+				}
+				mapping := idtools.IDMap{
+					ContainerID: int(cid),
+					HostID:      int(hid),
+					Size:        int(size),
+				}
+				idmap = append(idmap, mapping)
+			}
+		}
+		return idmap, nil
+	}
+	uid, err := parseIDMap(uidmap, "userns-uid-map")
+	if err != nil {
+		return nil, nil, err
+	}
+	gid, err := parseIDMap(gidmap, "userns-gid-map")
+	if err != nil {
+		return nil, nil, err
+	}
+	return uid, gid, nil
+}