Remove drive letter during formatAndMount causes subPath evalSymlink issue

[jingxu97]

In PR #166, we remove driver letter during formatAndMount due to the issue of driver letter runout. Now, volume mount will create symlink from volumeId to a path. e.g.,
mklink testlink \?\Volume{2f230ace-0000-0000-0000-010000000000}\

However, in subPath setup, https://github.com/kubernetes/kubernetes/blob/master/pkg/volume/util/subpath/subpath_windows.go#L53
filepath.EvalSymlinks(hostPath)
will fail with error: too many links.

We need to find another way to evaluate the symlink when driver letter is not assigned.

[andyzhangx]

actually I am the author of that code finalSubPath, err := filepath.EvalSymlinks(hostPath), can we skip this too many links directly in the code if hostPath starts with \, this should be bug in filepath.EvalSymlinks

Is that windows specific code, or will that open a hole in Linux symlink checking?

it's only in windows specific code

[jingxu97]

@andyzhangx you mean skip this EvalSymlinks check or if the error is "too many links", we ignore the error?

[liggitt]

Is that windows specific code, or will that open a hole in Linux symlink checking?

[andyzhangx]

if the error is "too many links"

if the error is "too many links" error and if hostPath starts with \, ignore error (only in Windows code)

[jingxu97]

@andyzhangx but that means we don't check symlink for subpath in this case. Then it will open up the security issue that was fixed by this symlink check, I think.

[jingxu97]

Is that windows specific code, or will that open a hole in Linux symlink checking?

This is mount_windows.go code. So the changes here will not affect linux symlink checking.

[networkimprov]

Re Go filepath.EvalSymlinks, see golang/go#40180

It is probably not a good solution to any problem, except to show an administrator where a certain path leads at this moment.

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