docker build: ensure a Dockerfile exists in src directory

[outrunthewolf]

Its possible for Docker to tar up entire directories when there is no Dockerfile present and send to the daemon.

For example, running this command in /home

docker build -t test .

Will tar up the entire directory and try and pipe that.

There's some concern a mistake made, could tie up a lot of system resources, fill up /tmp, or completely tie up the daemon.

fyi @SvenDowideit

[SvenDowideit]

I think @peterbraden 's patch for #2112 could be refactored to include testing for Dockerfile (shame that pushes that test from the daemon to the cli) - avoiding the unintentional DOS / mass IO.

this still won't mitigate the risks fully, taring up the entire filesystem and tossing it over the pipe probably needs to be chunked if it were intentional

[crosbymichael]

@outrunthewolf

Even if the CLI did check for an existing Dockerfile before uploading the build context that will not help if you place a Dockerfile in your root / and try to do a docker build.

What do you think the appropriate fix should be?

[unclejack]

@crosbymichael Perhaps we should disallow the use of / as the source directory, even if there's a Dockerfile? We'd check if / is the source directory and error out if it i; if it's not, then we can just check if there's a Dockerfile in that directory.

What do you think?

[outrunthewolf]

You could still tar up any other directory by accident with that solution.

A stupid question cos i'm not 100% clued up on everything. Why would I want to be able to specify a directory without a Docker file in it?

[unclejack]

@outrunthewolf Those two checks (verify that we're not using / and look for a Dockerfile first) would also help avoid uploading directories without a Dockerfile.