fix path traversal in mirror-images command

[xrstf]

What this PR does / why we need it:
This fixes https://github.com/kubermatic/kubermatic/security/code-scanning/1

What type of PR is this?
/kind bug

Does this PR introduce a user-facing change? Then add your Release Note here:

Fix potential path traversal in mirror-images command

Documentation:

NONE

[kubermatic-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xrstf

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• pkg/install/OWNERS [xrstf]

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[pkprzekwas]

/lgtm

[kubermatic-bot]

LGTM label has been added.

Git tree hash: 7bfa43663f8be723a3f65d95c625b33bbb964f73

[pkprzekwas]

/cherrypick release/v2.22

[kubermatic-bot]

@pkprzekwas: new pull request created: #12294

In response to this:

/cherrypick release/v2.22

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[pkprzekwas]

/cherrypick release/v2.21

[kubermatic-bot]

@pkprzekwas: #12293 failed to apply on top of branch "release/v2.21":

Applying: fix path traversal in mirror-images command
Using index info to reconstruct a base tree...
M	pkg/install/images/images.go
Falling back to patching base and 3-way merge...
Auto-merging pkg/install/images/images.go
CONFLICT (content): Merge conflict in pkg/install/images/images.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 fix path traversal in mirror-images command
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherrypick release/v2.21

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.