Strange "Permission denied" when trying to build C# Protobuf project inside Docker container

I have a fairly simple .net Core C# project with a .proto file. The .csproj looks like this:

<?xml version="1.0" encoding="utf-8"?>
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netstandard2.1</TargetFramework>
    <RootNamespace>My.Overview</RootNamespace>
  </PropertyGroup>
  <ItemGroup>
    <Protobuf Include="..\..\Protos\overview.proto" GrpcServices="Both" Link="Protos\overview.proto" />
  </ItemGroup>
  <Import Project="..\..\.paket\Paket.Restore.targets" />
</Project>

I have referenced this in an ASP.net Core 3.1 project, and I use Paket for resolution of dependencies.

When I compile this from Visual Studio or dotnet build everything works fine.

However I also want to build the service as a Docker container. The relevant portion of the Dockerfile looks like this:

RUN dotnet tool install -g paket
ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/.dotnet/tools

COPY paket.dependencies /build/
COPY paket.lock /build/
WORKDIR /build
RUN paket install
COPY . /build
RUN dotnet publish -c Release AppThatUses.My.Overview

When I docker build, I get this:

/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003: The specified task executable "/root/.nuget/packages/grpc.tools/2.29.0/tools/linux_x64/protoc" could not be run. System.ComponentModel.Win32Exception (13): Permission denied [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at System.Diagnostics.Process.ForkAndExecProcess(String filename, String[] argv, String[] envp, String cwd, Boolean redirectStdin, Boolean redirectStdout, Boolean redirectStderr, Boolean setCredentials, UInt32 userId, UInt32 groupId, UInt32[] groups, Int32& stdinFd, Int32& stdoutFd, Int32& stderrFd, Boolean usesTerminal, Boolean throwOnNoExec) [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at System.Diagnostics.Process.StartCore(ProcessStartInfo startInfo) [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at System.Diagnostics.Process.Start() [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at Microsoft.Build.Utilities.ToolTask.ExecuteTool(String pathToTool, String responseFileCommands, String commandLineCommands) [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at Microsoft.Build.Utilities.ToolTask.Execute() [/build/Model/Overview/Overview.csproj]
The command '/bin/sh -c dotnet publish -c Release AppThatUses.My.Overview' returned a non-zero code: 1

I investigated this and I saw that protoc was not executable, so I added this line just before the dotnet publish:

RUN find /root/.nuget/packages -name protoc |grep linux |xargs chmod +x

Now, I get:

/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003: The specified task executable "/root/.nuget/packages/grpc.tools/2.29.0/tools/linux_x64/protoc" could not be run. System.ComponentModel.Win32Exception (2): No such file or directory [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at System.Diagnostics.Process.ForkAndExecProcess(String filename, String[] argv, String[] envp, String cwd, Boolean redirectStdin, Boolean redirectStdout, Boolean redirectStderr, Boolean setCredentials, UInt32 userId, UInt32 groupId, UInt32[] groups, Int32& stdinFd, Int32& stdoutFd, Int32& stderrFd, Boolean usesTerminal, Boolean throwOnNoExec) [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at System.Diagnostics.Process.StartCore(ProcessStartInfo startInfo) [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at System.Diagnostics.Process.Start() [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at Microsoft.Build.Utilities.ToolTask.ExecuteTool(String pathToTool, String responseFileCommands, String commandLineCommands) [/build/Model/Overview/Overview.csproj]
/root/.nuget/packages/grpc.tools/2.29.0/build/_protobuf/Google.Protobuf.Tools.targets(264,5): error MSB6003:    at Microsoft.Build.Utilities.ToolTask.Execute() [/build/Model/Overview/Overview.csproj]

I triple-checked that /build/Model/Overview/Overview.csproj is actually there.

What am I missing?

Solution

Not a bugfix but a workaround:

For some reason, command-line tools installed via dotnet tool install are not executable
.net Core SDK 3.1 based on Alpine does not work, the "buster" one works

So, here's what I did:

Based my build stage on mcr.microsoft.com/dotnet/core/sdk:3.1-buster instead of mcr.microsoft.com/dotnet/core/sdk:3.1-alpine
Added the following line right before my dotnet build: RUN chmod -Rf +x /root/.nuget/packages/grpc.tools/2.29.0/tools

With these changes in place, the build works.