From f0329568b5afeddd03db4b969489e19a1bd2ee97 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Mon, 1 Jul 2024 17:14:27 +0200
Subject: [PATCH] GitFileSystemObjectSink: catch an overflow

---
 src/libfetchers/git-utils.cc        |  2 ++
 tests/unit/libfetchers/git-utils.cc | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/src/libfetchers/git-utils.cc b/src/libfetchers/git-utils.cc
index c41cfe683..64fd39aed 100644
--- a/src/libfetchers/git-utils.cc
+++ b/src/libfetchers/git-utils.cc
@@ -931,6 +931,8 @@ struct GitFileSystemObjectSinkImpl : GitFileSystemObjectSink
             ++dir;
             relTargetLeft = relTargetLeft.substr(3);
         }
+        if (dir == pendingDirs.rend())
+            throw Error("invalid hard link target '%s' for path '%s'", target, path);
 
         // Look up the remainder of the target, starting at the
         // top-most `git_treebuilder`.
diff --git a/tests/unit/libfetchers/git-utils.cc b/tests/unit/libfetchers/git-utils.cc
index c007d1c3c..3c06b593a 100644
--- a/tests/unit/libfetchers/git-utils.cc
+++ b/tests/unit/libfetchers/git-utils.cc
@@ -87,4 +87,24 @@ TEST_F(GitUtilsTest, sink_basic)
     ASSERT_EQ(accessor->readFile(CanonPath("links/foo")), "hello world");
 };
 
+TEST_F(GitUtilsTest, sink_hardlink)
+{
+    auto repo = openRepo();
+    auto sink = repo->getFileSystemObjectSink();
+
+    sink->createDirectory("foo-1.1");
+
+    sink->createRegularFile(
+        "foo-1.1/hello", [](CreateRegularFileSink & fileSink) { writeString(fileSink, "hello world", false); });
+
+    try {
+        sink->createHardlink("foo-1.1/link", CanonPath("hello"));
+        FAIL() << "Expected an exception";
+    } catch (const nix::Error & e) {
+        ASSERT_THAT(e.msg(), testing::HasSubstr("invalid hard link target"));
+        ASSERT_THAT(e.msg(), testing::HasSubstr("/hello"));
+        ASSERT_THAT(e.msg(), testing::HasSubstr("foo-1.1/link"));
+    }
+};
+
 } // namespace nix