cgroups: Parse correctly if cgroup path contains :

Prior to this change a cgroup with a `:` character in it's path was not
parsed correctly (as occurs on some instances of systemd cgroups under
some versions of systemd, e.g. 225 with accounting).

This fixes that issue and adds a test.

Signed-off-by: Euan Kemp <euank@coreos.com>

libcontainer/cgroups/utils.go

@@ -262,6 +262,8 @@ func readProcsFile(dir string) ([]int, error) {
 	return out, nil
 }
 
+// ParseCgroupFile parses the given cgroup file, typically from
+// /proc/<pid>/cgroup, into a map of subgroups to cgroup names.
 func ParseCgroupFile(path string) (map[string]string, error) {
 	f, err := os.Open(path)
 	if err != nil {
@@ -269,7 +271,12 @@ func ParseCgroupFile(path string) (map[string]string, error) {
 	}
 	defer f.Close()
 
-	s := bufio.NewScanner(f)
+	return parseCgroupFromReader(f)
+}
+
+// helper function for ParseCgroupFile to make testing easier
+func parseCgroupFromReader(r io.Reader) (map[string]string, error) {
+	s := bufio.NewScanner(r)
 	cgroups := make(map[string]string)
 
 	for s.Scan() {
@@ -278,7 +285,16 @@ func ParseCgroupFile(path string) (map[string]string, error) {
 		}
 
 		text := s.Text()
-		parts := strings.Split(text, ":")
+		// from cgroups(7):
+		// /proc/[pid]/cgroup
+		// ...
+		// For each cgroup hierarchy ... there is one entry
+		// containing three colon-separated fields of the form:
+		//     hierarchy-ID:subsystem-list:cgroup-path
+		parts := strings.SplitN(text, ":", 3)
+		if len(parts) < 3 {
+			return nil, fmt.Errorf("invalid cgroup entry: must contain at least two colons: %v", text)
+		}
 
 		for _, subs := range strings.Split(parts[1], ",") {
 			cgroups[subs] = parts[2]

libcontainer/cgroups/utils_test.go

@@ -4,6 +4,8 @@ package cgroups
 
 import (
 	"bytes"
+	"fmt"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -190,3 +192,56 @@ func BenchmarkGetCgroupMounts(b *testing.B) {
 		}
 	}
 }
+
+func TestParseCgroupString(t *testing.T) {
+	testCases := []struct {
+		input          string
+		expectedError  error
+		expectedOutput map[string]string
+	}{
+		{
+			// Taken from a CoreOS instance running systemd 225 with CPU/Mem
+			// accounting enabled in systemd
+			input: `9:blkio:/
+8:freezer:/
+7:perf_event:/
+6:devices:/system.slice/system-sshd.slice
+5:cpuset:/
+4:cpu,cpuacct:/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service
+3:net_cls,net_prio:/
+2:memory:/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service
+1:name=systemd:/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service`,
+			expectedOutput: map[string]string{
+				"name=systemd": "/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service",
+				"blkio":        "/",
+				"freezer":      "/",
+				"perf_event":   "/",
+				"devices":      "/system.slice/system-sshd.slice",
+				"cpuset":       "/",
+				"cpu":          "/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service",
+				"cpuacct":      "/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service",
+				"net_cls":      "/",
+				"net_prio":     "/",
+				"memory":       "/system.slice/system-sshd.slice/sshd@126-10.240.0.15:22-xxx.yyy.zzz.aaa:33678.service",
+			},
+		},
+		{
+			input:         `malformed input`,
+			expectedError: fmt.Errorf(`invalid cgroup entry: must contain at least two colons: malformed input`),
+		},
+	}
+
+	for ndx, testCase := range testCases {
+		out, err := parseCgroupFromReader(strings.NewReader(testCase.input))
+		if err != nil {
+			if testCase.expectedError == nil || testCase.expectedError.Error() != err.Error() {
+				t.Errorf("%v: expected error %v, got error %v", ndx, testCase.expectedError, err)
+			}
+		} else {
+			if !reflect.DeepEqual(testCase.expectedOutput, out) {
+				t.Errorf("%v: expected output %v, got error %v", ndx, testCase.expectedOutput, out)
+			}
+		}
+	}
+
+}