Unable to copy file via hard link when using buildkit

[tmarsh-cloudian]

When I attempt to copy a file into a container via a hard link, I get an error about the build context.

Version:

$ docker --version
Docker version 24.0.9-2, build 293681613032e6d1a39cc88115847d3984195c24

The following script reproduces the issue for me:

#! /bin/bash

set -euxo pipefail

cd "$(mktemp -d)"

echo 123 > myfile
ln myfile mylink

cat <<EOF > Dockerfile
FROM gcr.io/distroless/static:nonroot
COPY mylink /tmp
EOF

docker build --no-cache .

Outputs:

++ mktemp -d
+ cd /tmp/tmp.TScXE0bdOw
+ echo 123
+ ln myfile mylink
+ cat
+ docker build --no-cache .
[+] Building 1.2s (5/6)                                    docker:default
 => [internal] load .dockerignore                                    0.0s
 => => transferring context: 2B                                      0.0s
 => [internal] load build definition from Dockerfile                 0.0s
 => => transferring dockerfile: 92B                                  0.0s
 => [internal] load metadata for gcr.io/distroless/static:nonroot    1.1s
 => ERROR [internal] load build context                              0.0s
 => => transferring context: 33B                                     0.0s
 => [1/2] FROM gcr.io/distroless/static:nonroot@sha256:e9ac71e2b8e2  0.0s
 => => resolve gcr.io/distroless/static:nonroot@sha256:e9ac71e2b8e2  0.0s
------
 > [internal] load build context:
------
ERROR: failed to solve: invalid link mylink to unknown path: "myfile"

When I disable buildkit, by replacing the last line of my script with

DOCKER_BUILDKIT=0 docker build --no-cache .

The container is built as expected, output:

++ mktemp -d
+ cd /tmp/tmp.fmYpyPbRpy
+ echo 123
+ ln myfile mylink
+ cat
+ DOCKER_BUILDKIT=0
+ docker build --no-cache .
DEPRECATED: The legacy builder is deprecated and will be removed in a future release.
            BuildKit is currently disabled; enable it by removing the DOCKER_BUILDKIT=0
            environment-variable.

Sending build context to Docker daemon  3.584kB
Step 1/2 : FROM gcr.io/distroless/static:nonroot
nonroot: Pulling from distroless/static
b2ce0e066077: Pull complete 
e8d9a567199d: Pull complete 
058cf3d8c2ba: Pull complete 
b6824ed73363: Pull complete 
7c12895b777b: Pull complete 
33e068de2649: Pull complete 
5664b15f108b: Pull complete 
27be814a09eb: Pull complete 
4aa0ea1413d3: Pull complete 
da7816fa955e: Pull complete 
9aee425378d2: Pull complete 
Digest: sha256:e9ac71e2b8e279a8372741b7a0293afda17650d926900233ec3a7b2b7c22a246
Status: Downloaded newer image for gcr.io/distroless/static:nonroot
 ---> 9104641e0242
Step 2/2 : COPY mylink /tmp
 ---> eacd493fa464
Successfully built eacd493fa464

[jedevc]

I think this looks like a duplicate of #4831 - so closing this for now (if it's different, just shout, we can re-open! 🎉)

This should be fixed by #4870, which will be included in the upcoming v0.13.2 release: https://github.com/moby/buildkit/milestone/33

[tmarsh-cloudian]

Yeah looks the same, thanks