restrict log sym link filename to 255 characters

Signed-off-by: Vishnu Kannan <vishnuk@google.com>

pkg/kubelet/dockertools/docker.go

@@ -44,6 +44,7 @@ const (
 	PodInfraContainerName = leaky.PodInfraContainerName
 	DockerPrefix          = "docker://"
 	LogSuffix             = "log"
+	ext4MaxFileNameLen    = 255
 )
 
 const (
@@ -299,7 +300,13 @@ func ParseDockerName(name string) (dockerName *KubeletContainerName, hash uint64
 }
 
 func LogSymlink(containerLogsDir, podFullName, containerName, dockerId string) string {
-	return path.Join(containerLogsDir, fmt.Sprintf("%s_%s-%s.%s", podFullName, containerName, dockerId, LogSuffix))
+	suffix := fmt.Sprintf(".%s", LogSuffix)
+	logPath := fmt.Sprintf("%s_%s-%s", podFullName, containerName, dockerId)
+	// Length of a filename cannot exceed 255 characters in ext4 on Linux.
+	if len(logPath) > ext4MaxFileNameLen-len(suffix) {
+		logPath = logPath[:ext4MaxFileNameLen-len(suffix)]
+	}
+	return path.Join(containerLogsDir, logPath+suffix)
 }
 
 // Get a *dockerapi.Client, either using the endpoint passed in, or using

pkg/kubelet/dockertools/docker_test.go

@@ -20,6 +20,8 @@ import (
 	"encoding/json"
 	"fmt"
 	"hash/adler32"
+	"math/rand"
+	"path"
 	"reflect"
 	"sort"
 	"strconv"
@@ -800,3 +802,24 @@ func TestMilliCPUToQuota(t *testing.T) {
 		}
 	}
 }
+
+const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func randStringBytes(n int) string {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = letterBytes[rand.Intn(len(letterBytes))]
+	}
+	return string(b)
+}
+
+func TestLogSymLink(t *testing.T) {
+	as := assert.New(t)
+	containerLogsDir := "/foo/bar"
+	podFullName := randStringBytes(128)
+	containerName := randStringBytes(70)
+	dockerId := randStringBytes(80)
+	// The file name cannot exceed 255 characters. Since .log suffix is required, the prefix cannot exceed 251 characters.
+	expectedPath := path.Join(containerLogsDir, fmt.Sprintf("%s_%s-%s", podFullName, containerName, dockerId)[:251]+".log")
+	as.Equal(expectedPath, LogSymlink(containerLogsDir, podFullName, containerName, dockerId))
+}