just-mr setup: Fix ensuring 'subdir' only accepts non-upwards paths

...which implicitly also enforces non-absolute.

This ensures that there is no access outside the root directory of
a Git checkout or the temporary unpack directory of an archive.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/other_tools/utils/parse_archive.cpp b/src/other_tools/utils/parse_archive.cpp
index 50b9d4a3..e31109a9 100644
--- a/src/other_tools/utils/parse_archive.cpp
+++ b/src/other_tools/utils/parse_archive.cpp
@@ -26,6 +26,7 @@
 #include "src/buildtool/crypto/hash_function.hpp"
 #include "src/buildtool/crypto/hash_info.hpp"
 #include "src/buildtool/file_system/symlinks_map/pragma_special.hpp"
+#include "src/utils/cpp/path.hpp"
 
 auto ParseArchiveContent(ExpressionPtr const& repo_desc,
                          std::string const& origin)
@@ -129,9 +130,9 @@ auto ParseArchiveDescription(ExpressionPtr const& repo_desc,
                                             ? repo_desc_subdir->String()
                                             : "")
                       .lexically_normal();
-    if (subdir.is_absolute()) {
+    if (not PathIsNonUpwards(subdir)) {
         (*logger)(fmt::format("ArchiveCheckout: Expected field \"subdir\" to "
-                              "be a relative path, but found {}",
+                              "be a non-upwards path, but found {}",
                               subdir.string()),
                   /*fatal=*/true);
         return std::nullopt;