`ADD` fails to add Git repository on Windows: `unable to access '\\.\GLOBALROOT\Device\Null/.config/git/config': Invalid argument`

[slonopotamus]

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Bug description

ADD for Git repo fails on Windows when buildx/BuildKit is used.

Reproduction

Use a Windows machine (Windows 11 in my case, but specific version is not important, you might just need to adjust base image version).

Set up dockerd using your preferred way.

Create an empty directory.

Place a Dockerfile in it:

FROM mcr.microsoft.com/windows/nanoserver:ltsc2022
ADD https://github.com/moby/moby.git C:\\moby

Run docker buildx build .

Expected: build succeeds

Actual:

$ docker buildx build .
[+] Building 16.9s (6/6) FINISHED                                                                                                                           docker:default
 => [internal] load build definition from Dockerfile                                                                                                                  0.0s
 => => transferring dockerfile: 135B                                                                                                                                  0.0s 
 => [internal] load metadata for mcr.microsoft.com/windows/nanoserver:ltsc2022                                                                                        0.8s 
 => [internal] load .dockerignore                                                                                                                                     0.0s
 => => transferring context: 139B                                                                                                                                     0.0s 
 => [1/2] FROM mcr.microsoft.com/windows/nanoserver:ltsc2022@sha256:60612a30303eb5a15ce7f53fa2eecf70bca41d72657de0482fbde601ae5f3403                                 15.8s 
 => => resolve mcr.microsoft.com/windows/nanoserver:ltsc2022@sha256:60612a30303eb5a15ce7f53fa2eecf70bca41d72657de0482fbde601ae5f3403                                  0.0s 
 => => sha256:c8c762a2c2783d40d4a09719516adec866b153c94682ef9c4c672227f2f21573 122.71MB / 122.71MB                                                                    4.5s 
 => => extracting sha256:c8c762a2c2783d40d4a09719516adec866b153c94682ef9c4c672227f2f21573                                                                            11.2s
 => ERROR [2/2] ADD https://github.com/moby/moby.git C:/moby                                                                                                         15.9s
 => CANCELED [2/2] ADD https://github.com/moby/moby.git C:/moby                                                                                                       0.0s 
------                                                                                                                                                                     
 > [2/2] ADD https://github.com/moby/moby.git C:/moby:                                                                                                                     
1.037 ref: refs/heads/master    HEAD                                                                                                                                       
1.037 a52171f5eeb6e553e7c4744abf6b722962b2aca4  HEAD                                                                                                                       
2.080 a52171f5eeb6e553e7c4744abf6b722962b2aca4  refs/heads/master                                                                                                          
3.237 ref: refs/heads/master    HEAD
3.237 a52171f5eeb6e553e7c4744abf6b722962b2aca4  HEAD
4.149 a52171f5eeb6e553e7c4744abf6b722962b2aca4
15.09 fatal: unable to access '\\.\GLOBALROOT\Device\Null/.config/git/config': Invalid argument
15.10 /mingw64/libexec/git-core/git-sh-setup: line 46: /git-sh-i18n: No such file or directory
------
ERROR: failed to build: failed to solve: failed to update submodules for https://github.com/moby/moby.git: git stderr:
fatal: unable to access '\\.\GLOBALROOT\Device\Null/.config/git/config': Invalid argument
/mingw64/libexec/git-core/git-sh-setup: line 46: /git-sh-i18n: No such file or directory
: exit status 1

Version information

Reproes with moby 28.5.1. Also reproes with today latest master branch (commit a52171f5eeb6e553e7c4744abf6b722962b2aca4).

I believe this can also be reproduced by using buildctl + buildkitd without moby.

Debugging shows that it fails when checking out submodules.