add pkg/capabilities

Add pkg/capabibilities to deal with capabilities.  The code has been
copied from Docker (and attributed with the copyright) but changed
significantly to only do what we really need.  The code has also been
simplified and will perform better due to removed redundancy.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 129 insertions, 0 deletions

diff --git a/pkg/capabilities/capabilities.go b/pkg/capabilities/capabilities.go
new file mode 100644
index 000000000..ea22498b8
--- /dev/null
+++ b/pkg/capabilities/capabilities.go
@@ -0,0 +1,129 @@
+package capabilities
+
+// Copyright 2013-2018 Docker, Inc.
+
+// NOTE: this package has been copied from github.com/docker/docker but been
+//       changed significantly to fit the needs of libpod.
+
+import (
+	"strings"
+
+	"github.com/containers/libpod/pkg/util"
+	"github.com/pkg/errors"
+	"github.com/syndtr/gocapability/capability"
+)
+
+var (
+	// Used internally and populated during init().
+	capabilityList []string
+
+	// ErrUnknownCapability is thrown when an unknown capability is processed.
+	ErrUnknownCapability = errors.New("unknown capability")
+)
+
+// All is a special value used to add/drop all known capababilities.
+// Useful on the CLI for `--cap-add=all` etc.
+const All = "ALL"
+
+func init() {
+	last := capability.CAP_LAST_CAP
+	// hack for RHEL6 which has no /proc/sys/kernel/cap_last_cap
+	if last == capability.Cap(63) {
+		last = capability.CAP_BLOCK_SUSPEND
+	}
+	for _, cap := range capability.List() {
+		if cap > last {
+			continue
+		}
+		capabilityList = append(capabilityList, "CAP_"+strings.ToUpper(cap.String()))
+	}
+}
+
+// AllCapabilities returns all known capabilities.
+func AllCapabilities() []string {
+	return capabilityList
+}
+
+// normalizeCapabilities normalizes caps by adding a "CAP_" prefix (if not yet
+// present).
+func normalizeCapabilities(caps []string) ([]string, error) {
+	normalized := make([]string, len(caps))
+	for i, c := range caps {
+		c = strings.ToUpper(c)
+		if c == All {
+			normalized = append(normalized, c)
+			continue
+		}
+		if !strings.HasPrefix(c, "CAP_") {
+			c = "CAP_" + c
+		}
+		if !util.StringInSlice(c, capabilityList) {
+			return nil, errors.Wrapf(ErrUnknownCapability, "%q", c)
+		}
+		normalized[i] = c
+	}
+	return normalized, nil
+}
+
+// ValidateCapabilities validates if caps only contains valid capabilities.
+func ValidateCapabilities(caps []string) error {
+	for _, c := range caps {
+		if !util.StringInSlice(c, capabilityList) {
+			return errors.Wrapf(ErrUnknownCapability, "%q", c)
+		}
+	}
+	return nil
+}
+
+// MergeCapabilities computes a set of capabilities by adding capapbitilities
+// to or dropping them from base.
+//
+// Note that "ALL" will cause all known capabilities to be added/dropped but
+// the ones specified to be dropped/added.
+func MergeCapabilities(base, adds, drops []string) ([]string, error) {
+	if len(adds) == 0 && len(drops) == 0 {
+		// Nothing to tweak; we're done
+		return base, nil
+	}
+
+	capDrop, err := normalizeCapabilities(drops)
+	if err != nil {
+		return nil, err
+	}
+	capAdd, err := normalizeCapabilities(adds)
+	if err != nil {
+		return nil, err
+	}
+
+	// Make sure that capDrop and capAdd are distinct sets.
+	for _, drop := range capDrop {
+		if util.StringInSlice(drop, capAdd) {
+			return nil, errors.Errorf("capability %q cannot be dropped and added", drop)
+		}
+	}
+
+	var caps []string
+
+	switch {
+	case util.StringInSlice(All, capAdd):
+		// Add all capabilities except ones on capDrop
+		for _, c := range capabilityList {
+			if !util.StringInSlice(c, capDrop) {
+				caps = append(caps, c)
+			}
+		}
+	case util.StringInSlice(All, capDrop):
+		// "Drop" all capabilities; use what's in capAdd instead
+		caps = capAdd
+	default:
+		// First drop some capabilities
+		for _, c := range base {
+			if !util.StringInSlice(c, capDrop) {
+				caps = append(caps, c)
+			}
+		}
+		// Then add the list of capabilities from capAdd
+		caps = append(caps, capAdd...)
+	}
+	return caps, nil
+}