[18.09 backport] Fix docker cp when container source path is /

[thaJeztah]

backport of moby#39357 for 18.09

Another attempt at fixing moby#39348
Fixes moby#39348
Previous attempt at moby#39351

Before 7a7357d, archive.TarResourceRebase was being used to copy files
and folders from the container. That function splits the source path
into a dirname + basename pair to support copying a file:
if you wanted to tar dir/file it would tar from dir the file file
(as part of the IncludedFiles option).

However, that path splitting logic was kept for folders as well, which
resulted in weird inputs to archive.TarWithOptions:
if you wanted to tar dir1/dir2 it would tar from dir1 the directory
dir2 (as part of IncludedFiles option).

Although it was weird, it worked fine until we started chrooting into
the container rootfs when doing a docker cp with container source set
to / (cf 3029e76 (moby#39292)).

The fix is to only do the path splitting logic if the source is a file.

Unfortunately, 7a7357d added support for LCOW by duplicating some of
this subtle logic. Ideally we would need to do more refactoring of the
archive codebase to properly encapsulate these behaviors behind well-
documented APIs.

This fix does not do that. Instead, it fixes the issue inline.

Signed-off-by: Tibor Vass [email protected]

I added a couple of more tests than the actual issue needs, just to make sure there are no other regressions compared to before the cve fix (3029e76).

Huge thanks to @cpuguy83 ❤️who worked tirelessly with me to understand the code and make this PR.

[thaJeztah]

ping @tiborvass @kolyshkin @andrewhsu PTAL

[cpuguy83]

integration/container/copy_test.go:108:26:warning: cannot use ctx (variable of type context.Context) as *testing.T value in argument to container.Create (gosimple)

[thaJeztah]

ah, booh

[thaJeztah]

cherry-picked 8f4b96f

[thaJeztah]

only failures are DockerSuite.TestRunInteractiveWithRestartPolicy on experimental https://jenkins.dockerproject.org/job/Docker-PRs-experimental/45728/console

tracked through moby#39352

17:30:53 FAIL: docker_cli_run_test.go:1792: DockerSuite.TestRunInteractiveWithRestartPolicy
17:30:53 
17:30:53 assertion failed: 
17:30:53 Command:  /usr/local/cli/docker run -i --name test-inter-restart --restart=always busybox sh
17:30:53 ExitCode: 0
17:30:53 Error:    <nil>
17:30:53 Stdout:   
17:30:53 Stderr:   
17:30:53 
17:30:53 Failures:
17:30:53 ExitCode was 0 expected 11

and on Janky https://jenkins.dockerproject.org/job/Docker-PRs/54598/console

17:44:53 FAIL: docker_cli_start_test.go:190: DockerSuite.TestStartReturnCorrectExitCode
17:44:53 
17:44:53 assertion failed: expected an error, got nil

[andrewhsu]

@kolyshkin kicked job again: https://jenkins.dockerproject.org/job/Docker-PRs/54613/console

[kolyshkin]

kicked the janky ci as I haven't seen this earlier:

17:44:53 FAIL: docker_cli_start_test.go:190: DockerSuite.TestStartReturnCorrectExitCode

and it looks like another manifestation of that elusive flakiness we have it TestRunInteractiveWithRestartPolicy

[andrewhsu]

Looks like latest job run has success:

...
PASS: docker_cli_run_test.go:1792: DockerSuite.TestRunInteractiveWithRestartPolicy	11.104s
...
PASS: docker_cli_start_test.go:190: DockerSuite.TestStartReturnCorrectExitCode	2.289s
...

[andrewhsu]

LGTM