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pathrs: add "hallucination" helpers for SecureJoin magic

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In order to maintain compatibility with previous releases of runc (which
permitted dangling symlinks as path components by permitting
non-existent path components to be treated like real directories) we
have to first do SecureJoin to construct a target path that is
compatible with the old behaviour but has all dangling symlinks (or
other invalid paths like ".." components after non-existent directories)
removed.

This is effectively a more generic verison of commit 3f925525b4
("rootfs: re-allow dangling symlinks in mount targets") and will let us
remove the need for open-coding SecureJoin workarounds.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
This commit is contained in:
Aleksa Sarai
2025-11-09 01:41:10 +11:00
parent 20c5a8ec4a
commit cfb74326be
4 changed files with 40 additions and 25 deletions
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internal/pathrs/root_pathrslite.go
+5
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@@ -50,6 +50,11 @@ func OpenInRoot(root, subpath string, flags int) (*os.File, error) {
// include it in the passed flags. The fileMode argument uses unix.* mode bits,
// *not* os.FileMode.
func CreateInRoot(root, subpath string, flags int, fileMode uint32) (*os.File, error) {
subpath, err := hallucinateUnsafePath(root, subpath)
if err != nil {
return nil, fmt.Errorf("failed to construct hallucinated target path: %w", err)
}
dir, filename := filepath.Split(subpath)
if filepath.Join("/", filename) == "/" {
return nil, fmt.Errorf("create in root subpath %q has bad trailing component %q", subpath, filename)