AppArmor: runtime check if it's enabled on the host

Check at runtime if AppArmor is enabled on the host.

Signed-off-by: Valentin Rothberg <vrothberg@suse.com>

Closes: #1128
Approved by: mheon

vendor/github.com/opencontainers/runc/libcontainer/apparmor/apparmor.go

@@ -0,0 +1,54 @@
+// +build apparmor,linux
+
+package apparmor
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+// IsEnabled returns true if apparmor is enabled for the host.
+func IsEnabled() bool {
+	if _, err := os.Stat("/sys/kernel/security/apparmor"); err == nil && os.Getenv("container") == "" {
+		if _, err = os.Stat("/sbin/apparmor_parser"); err == nil {
+			buf, err := ioutil.ReadFile("/sys/module/apparmor/parameters/enabled")
+			return err == nil && len(buf) > 1 && buf[0] == 'Y'
+		}
+	}
+	return false
+}
+
+func setprocattr(attr, value string) error {
+	// Under AppArmor you can only change your own attr, so use /proc/self/
+	// instead of /proc/<tid>/ like libapparmor does
+	path := fmt.Sprintf("/proc/self/attr/%s", attr)
+
+	f, err := os.OpenFile(path, os.O_WRONLY, 0)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = fmt.Fprintf(f, "%s", value)
+	return err
+}
+
+// changeOnExec reimplements aa_change_onexec from libapparmor in Go
+func changeOnExec(name string) error {
+	value := "exec " + name
+	if err := setprocattr("exec", value); err != nil {
+		return fmt.Errorf("apparmor failed to apply profile: %s", err)
+	}
+	return nil
+}
+
+// ApplyProfile will apply the profile with the specified name to the process after
+// the next exec.
+func ApplyProfile(name string) error {
+	if name == "" {
+		return nil
+	}
+
+	return changeOnExec(name)
+}

vendor/github.com/opencontainers/runc/libcontainer/apparmor/apparmor_disabled.go

@@ -0,0 +1,20 @@
+// +build !apparmor !linux
+
+package apparmor
+
+import (
+	"errors"
+)
+
+var ErrApparmorNotEnabled = errors.New("apparmor: config provided but apparmor not supported")
+
+func IsEnabled() bool {
+	return false
+}
+
+func ApplyProfile(name string) error {
+	if name != "" {
+		return ErrApparmorNotEnabled
+	}
+	return nil
+}