kubernetes/vendor/github.com/cyphar/filepath-securejoin/join.go

const maxSymlinkLimit …

// IsNotExist tells you if err is an error that implies that either the path
// accessed does not exist (or path components don't exist). This is
// effectively a more broad version of [os.IsNotExist].
func IsNotExist(err error) bool { … }

// SecureJoinVFS joins the two given path components (similar to [filepath.Join]) except
// that the returned path is guaranteed to be scoped inside the provided root
// path (when evaluated). Any symbolic links in the path are evaluated with the
// given root treated as the root of the filesystem, similar to a chroot. The
// filesystem state is evaluated through the given [VFS] interface (if nil, the
// standard [os].* family of functions are used).
//
// Note that the guarantees provided by this function only apply if the path
// components in the returned string are not modified (in other words are not
// replaced with symlinks on the filesystem) after this function has returned.
// Such a symlink race is necessarily out-of-scope of SecureJoinVFS.
//
// NOTE: Due to the above limitation, Linux users are strongly encouraged to
// use [OpenInRoot] instead, which does safely protect against these kinds of
// attacks. There is no way to solve this problem with SecureJoinVFS because
// the API is fundamentally wrong (you cannot return a "safe" path string and
// guarantee it won't be modified afterwards).
//
// Volume names in unsafePath are always discarded, regardless if they are
// provided via direct input or when evaluating symlinks. Therefore:
//
// "C:\Temp" + "D:\path\to\file.txt" results in "C:\Temp\path\to\file.txt"
func SecureJoinVFS(root, unsafePath string, vfs VFS) (string, error) { … }

// SecureJoin is a wrapper around [SecureJoinVFS] that just uses the [os].* library
// of functions as the [VFS]. If in doubt, use this function over [SecureJoinVFS].
func SecureJoin(root, unsafePath string) (string, error) { … }