.net8 build an image problem

[Chris Dai]

What version of Docker.DotNet?:

3.125.4  3.125.15

Steps to reproduce the issue:

1. Create an ASP.NET Core WebApi 8.0 project
2. Add Docker support
3. Use the current project and Dockerfile to call the BuildImageFromDockerfileAsync method to build the image
4. Run container using image

Dockerfile

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
USER app
WORKDIR /app
EXPOSE 8080
EXPOSE 8081

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
ARG BUILD_CONFIGURATION=Release
WORKDIR /src
COPY ["WebApplication1/WebApplication1.csproj", "WebApplication1/"]
RUN dotnet restore "./WebApplication1/./WebApplication1.csproj"
COPY . .
WORKDIR "/src/WebApplication1"
RUN dotnet build "./WebApplication1.csproj" -c $BUILD_CONFIGURATION -o /app/build

FROM build AS publish
ARG BUILD_CONFIGURATION=Release
RUN dotnet publish "./WebApplication1.csproj" -c $BUILD_CONFIGURATION -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "WebApplication1.dll"]

What actually happened?:
Unhandled exception. System.UnauthorizedAccessException: Access to the path '/app/appsettings.json' is denied.
---> System.IO.IOException: Permission denied
--- End of inner exception stack trace ---
at Interop.ThrowExceptionForIoErrno(ErrorInfo errorInfo, String path, Boolean isDirError)
at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String path, OpenFlags flags, Int32 mode, Boolean failForSymlink, Boolean& wasSymlink, Func4 createOpenException) at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, UnixFileMode openPermissions, Int64& fileLength, UnixFileMode& filePermissions, Boolean failForSymlink, Boolean& wasSymlink, Func4 createOpenException)
at System.IO.Strategies.OSFileStreamStrategy..ctor(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable1 unixCreateMode) at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, Int64 preallocationSize) at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options) at Microsoft.Extensions.Configuration.FileConfigurationProvider.<Load>g__OpenRead|6_0(IFileInfo fileInfo) at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load(Boolean reload) at Microsoft.Extensions.Configuration.ConfigurationManager.AddSource(IConfigurationSource source) at Microsoft.Extensions.Configuration.ConfigurationManager.Microsoft.Extensions.Configuration.IConfigurationBuilder.Add(IConfigurationSource source) at Microsoft.Extensions.Hosting.HostingHostBuilderExtensions.ApplyDefaultAppConfiguration(HostBuilderContext hostingContext, IConfigurationBuilder appConfigBuilder, String[] args) at Microsoft.Extensions.Hosting.HostApplicationBuilder..ctor(HostApplicationBuilderSettings settings) at Microsoft.AspNetCore.Builder.WebApplicationBuilder..ctor(WebApplicationOptions options, Action1 configureDefaults)
at Microsoft.AspNetCore.Builder.WebApplication.CreateBuilder(String[] args)
at Program.

$(String[] args) in /src/WebApplication1/Program.cs:line 1

Additional information:
The main reason is because .net8 uses non-root user, but there is no problem when I use docker cli.

[Chris Dai]

I found the problem, I was using the ICSharpCode.SharpZipLib library, and each entry in the tar archive needed to set permissions.

The value of the Mode attribute is an octal number indicating the read, write, and execute permissions for the file. The format of this value is the same as permissions in Linux file systems.

TarEntry.TarHeader.Mode = Convert.ToInt32("0755", 8);