docker build fails with "archive/tar: write too long" when .dockerignore is a symlink

[krwc]

• This is a bug report
• This is a feature request
• I searched existing issues before opening this one

Expected behavior

docker build should succeed no matter if .dockerignore is a symlink or not.

Actual behavior

Build fails with strange looking "archive/tar: write too long" error.

Steps to reproduce the behavior

Minimal example: docker_failure.zip

Imagine you have the following directory tree (as in the docker_failure.zip, note the .dockerignore is a symlink):

$ tree -a
.
├── Dockerfile
└── test
    ├── .dockerignore -> ignore
    └── ignore

1 directory, 3 files

When we enter test and try to build the image, we have an error:

$ cd test
$ docker build --no-cache --file ../Dockerfile .
Sending build context to Docker daemon     512B
error during connect: Post "http://%2Fvar%2Frun%2Fdocker.sock/v1.40/build?buildargs=%7B%7D&cachefrom=%5B%5D&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=.dockerfile.fc23a238662d3ee404bd&labels=%7B%7D&memory=0&memswap=0&networkmode=default&nocache=1&rm=1&shmsize=0&target=&ulimits=null&version=1": archive/tar: write too long

I noticed two things:

1. When .dockerignore is not a symlink, the build succeeds.
2. When .dockerignore is/isn't a symlink, but the Dockerfile is in the same directory as working directory of docker build, the build succeeds.

Output of docker version:

Client:
 Version:           19.03.11-ce
 API version:       1.40
 Go version:        go1.14.3
 Git commit:        42e35e61f3
 Built:             Tue Jun  2 15:09:26 2020
 OS/Arch:           linux/amd64
 Experimental:      false

Server:
 Engine:
  Version:          19.03.11-ce
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.14.3
  Git commit:       42e35e61f3
  Built:            Tue Jun  2 15:09:05 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v1.3.4.m
  GitCommit:        d76c121f76a5fc8a462dc64594aea72fe18e1178.m
 runc:
  Version:          1.0.0-rc10
  GitCommit:        dc9208a3303feef5b3839f4323d9beb36df0a9dd
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683

Output of docker info:

Client:
 Debug Mode: false

Server:
 Containers: 65
  Running: 0
  Paused: 0
  Stopped: 65
 Images: 16
 Server Version: 19.03.11-ce
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: d76c121f76a5fc8a462dc64594aea72fe18e1178.m
 runc version: dc9208a3303feef5b3839f4323d9beb36df0a9dd
 init version: fec3683
 Security Options:
  seccomp
   Profile: default
 Kernel Version: 5.7.6-arch1-1
 Operating System: Arch Linux
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 31.02GiB
 Name: coffeeriver
 ID: ABVL:KPYK:AWYL:KX5K:HONY:EI25:4ARU:U7Z4:P5PB:6RSU:EPQ3:RZXJ
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional environment details (AWS, VirtualBox, physical, etc.)

It fails on physical machine. Didn't test anything else.