Confine Updater and Plugin Archive Extraction to the Target Directory (#15957)

* Confine Updater Archive Extraction to the Target Directory

The preset updater extracted downloaded archives by appending each entry
name to the cache directory, and the network plugin installer did the same
for the plugin folder, without checking that the result stays inside it.

Move the updater's extraction into libslic3r as extract_archive_confined,
which validates every entry with is_path_within_root before writing
anything and fails the whole archive if one entry resolves outside the
target. The plugin installer now rejects such an entry the same way. Well
formed archives extract exactly as before.

* Harden Archive Extraction Against Symlinks

The plugin installer now creates a symlink entry only when its target is
relative and, joined to the link's own directory, passes
is_path_within_root, via the new is_symlink_target_within_root helper.
Before writing any entry it checks the destination with symlink_status, so
an existing symlink, dangling or not, is replaced rather than followed, and
it creates parent directories inside the existing error handling.
extract_archive_confined replaces a symlink at a destination file the same
way.

is_path_within_root now ignores a trailing separator on the root, which
previously made every path fail the check.

* Validate Plugin Symlink Targets Before Replacing Existing Files

A symlink entry's target is now read and checked before anything already
at its destination is removed or renamed aside, so an archive rejected
for its link target leaves the installed plugin files in place.

* Reject Paths with an Embedded NUL When Confining Extraction

is_path_within_root compared each component with "..", so a name such
as "..\0" passed the check. The filesystem calls stop at the NUL and
act on a shorter path than the one that was checked: a symlink target
read from a plugin archive as raw bytes was created as "..", pointing
out of the plugin directory.

A path containing a NUL is now rejected before anything touches the
filesystem, which covers every caller, including entry names taken from
the Unicode Path extra field.

tests/libslic3r/test_utils.cpp

@@ -243,3 +243,82 @@ TEST_CASE("find_unused_filename gives up after 999 versions", "[Utils]") {
     REQUIRE_FALSE(find_unused_filename(dir.path(), "model.3mf", {}, name));
     CHECK(name == "model(999).3mf");
 }
+
+TEST_CASE("is_path_within_root accepts a root given with a trailing separator", "[utils]") {
+    ScopedTemporaryDir tmp;
+    const std::string root = tmp.path().string();
+    const std::string with_separator = GENERATE_COPY(root + "/", root + std::string(1, static_cast<char>(boost::filesystem::path::preferred_separator)));
+
+    CAPTURE(with_separator);
+    CHECK(is_path_within_root("vendor.json", with_separator));
+    CHECK(is_path_within_root("vendor/machine/printer.json", with_separator));
+    CHECK_FALSE(is_path_within_root("../vendor.json", with_separator));
+}
+
+TEST_CASE("is_path_within_root treats Windows-specific name forms the same on every platform", "[utils]") {
+    ScopedTemporaryDir tmp;
+
+    SECTION("names ending in dots or spaces stay inside the root") {
+        const std::string name = GENERATE(std::string("name."), std::string("name "), std::string("dir./file.json"), std::string("dir /file.json"));
+        CAPTURE(name);
+        CHECK(is_path_within_root(name, tmp.path()));
+    }
+    SECTION("drive-relative names are rejected") {
+        const std::string name = GENERATE(std::string("C:x"), std::string("c:x/y.json"), std::string("C:"));
+        CAPTURE(name);
+        CHECK_FALSE(is_path_within_root(name, tmp.path()));
+    }
+}
+
+TEST_CASE("is_path_within_root rejects a name with an embedded NUL", "[utils]") {
+    ScopedTemporaryDir tmp;
+    // The filesystem calls stop at the NUL, so they would act on a different path than the one checked.
+    const std::string name = GENERATE(std::string("..\0", 3), std::string("..\0x/file.json", 14), std::string("sub/..\0x", 8),
+                                      std::string("file.json\0", 10), std::string("\0file.json", 10));
+    CAPTURE(name.size());
+    CHECK_FALSE(is_path_within_root(name, tmp.path()));
+}
+
+TEST_CASE("is_symlink_target_within_root accepts relative targets that stay inside the root", "[utils]") {
+    ScopedTemporaryDir tmp;
+    const auto [link, target] = GENERATE(std::make_pair(std::string("Versions/Current"), std::string("A")),
+                                         std::make_pair(std::string("Foo.framework/Foo"), std::string("Versions/Current/Foo")),
+                                         std::make_pair(std::string("libfoo.so"), std::string("libfoo.so.1")),
+                                         std::make_pair(std::string("a/b/link"), std::string("c/d")));
+    CAPTURE(link, target);
+    CHECK(is_symlink_target_within_root(link, target, tmp.path()));
+}
+
+TEST_CASE("is_symlink_target_within_root rejects absolute targets and targets that climb out", "[utils]") {
+    ScopedTemporaryDir tmp;
+    const std::string outside = (tmp.path().parent_path() / "outside").generic_string();
+    const auto [link, target] = GENERATE_COPY(std::make_pair(std::string("sub/link"), outside),
+                                              std::make_pair(std::string("sub/link"), std::string("/etc/passwd")),
+                                              std::make_pair(std::string("sub/link"), std::string("\\outside")),
+                                              std::make_pair(std::string("sub/link"), std::string("C:/outside")),
+                                              std::make_pair(std::string("sub/link"), std::string("C:outside")),
+                                              std::make_pair(std::string("sub/link"), std::string("")),
+                                              std::make_pair(std::string("link"), std::string("..")),
+                                              std::make_pair(std::string("link"), std::string("../outside")),
+                                              std::make_pair(std::string("sub/link"), std::string("../../outside")),
+                                              std::make_pair(std::string("sub/link"), std::string("x/../../../outside")),
+                                              std::make_pair(std::string("sub/link"), std::string("..\\..\\outside")),
+                                              // symlink() stops at the NUL, so this target would be created as "..".
+                                              std::make_pair(std::string("link"), std::string("..\0", 3)));
+    CAPTURE(link, target);
+    CHECK_FALSE(is_symlink_target_within_root(link, target, tmp.path()));
+}
+
+#ifndef _WIN32
+TEST_CASE("is_symlink_target_within_root rejects a target that passes through a symlink leading out", "[utils]") {
+    ScopedTemporaryDir tmp;
+    const boost::filesystem::path root    = tmp.path() / "root";
+    const boost::filesystem::path outside = tmp.path() / "outside";
+    boost::filesystem::create_directories(root);
+    boost::filesystem::create_directories(outside);
+    boost::filesystem::create_symlink(outside, root / "out");
+
+    CHECK_FALSE(is_symlink_target_within_root("link", "out/lib.so", root));
+    CHECK(is_symlink_target_within_root("link", "in/lib.so", root));
+}
+#endif