cp: Fix broken symlinks to parent-dir

According to the GNU cp official documentation[1], a symlink is only
created if all source paths are absolute, unless the destination files
are in the current directory.

This fix solves this GNU cp incompatibility by:
- Adding verifications when handling symlinks, to ensure that a symlink
  with relative path are only created if the destination is within the
  current directory.
- Adding unit tests to cover this modifications, and ensure the behavior
  is correctly align with GNU documentation.

[1]:
https://www.gnu.org/software/coreutils/manual/html_node/cp-invocation.html#index-_002ds-16

src/uu/cp/src/cp.rs

@@ -7,6 +7,7 @@
 use quick_error::quick_error;
 use std::cmp::Ordering;
 use std::collections::{HashMap, HashSet};
+use std::env;
 #[cfg(not(windows))]
 use std::ffi::CString;
 use std::fs::{self, File, Metadata, OpenOptions, Permissions};
@@ -1864,6 +1865,22 @@ fn handle_copy_mode(
  if dest.exists() && options.overwrite == OverwriteMode::Clobber(ClobberMode::Force) {
  fs::remove_file(dest)?;
  }
+ if source.is_relative() {
+ let current_dir = env::current_dir()?;
+ let abs_dest =
+ canonicalize(dest, MissingHandling::Missing, ResolveMode::Physical).unwrap();
+ if let Some(parent) = abs_dest.parent() {
+ if parent != current_dir {
+ {
+ return Err(format!(
+ "{}: can make relative symbolic links only in current directory",
+ dest.maybe_quote()
+ )
+ .into());
+ }
+ }
+ }
+ }
  symlink_file(source, dest, symlinked_files)?;
  }
  CopyMode::Update => {

tests/by-util/test_cp.rs

@@ -5573,3 +5573,31 @@ fn test_preserve_attrs_overriding_2() {
  assert_ne!(dest_file1_metadata.ino(), dest_file2_metadata.ino());
  }
 }
+
+#[test]
+fn test_symlink_to_subdir() {
+ let (at, mut ucmd) = at_and_ucmd!();
+
+ at.touch("file");
+ at.mkdir("dir");
+
+ ucmd.args(&["--symbolic", "file", "dir"])
+ .fails()
+ .no_stdout()
+ .stderr_is("cp: dir/file: can make relative symbolic links only in current directory\n");
+
+ assert!(at.dir_exists("dir"));
+ assert!(!at.file_exists("dir/file"));
+}
+
+#[test]
+fn test_symlink_from_subdir() {
+ let (at, mut ucmd) = at_and_ucmd!();
+
+ at.mkdir("dir");
+ at.touch("dir/file");
+
+ ucmd.args(&["--symbolic", "dir/file", "."]).succeeds();
+
+ assert!(at.symlink_exists("file"));
+}