fix: keep multi outputs under target directory

sjsonnet/src-jvm-native/sjsonnet/SjsonnetMainBase.scala

@@ -421,6 +421,20 @@ object SjsonnetMainBase {
       case e: Error                    => Left(Error.formatError(e, maxTrace))
     }
 
+  private def multiOutputPath(multiPath: String, fileName: String): Either[String, os.FilePath] =
+    Try {
+      // Multi output names must stay under the requested output directory.
+      val normalizedFileName = fileName.dropWhile(_ == '/')
+      (os.FilePath(multiPath) / os.SubPath(normalizedFileName)).asInstanceOf[os.FilePath]
+    }.toEither.left.map {
+      case e: IllegalArgumentException
+          if Option(e.getMessage).exists(_.contains("ups must be zero")) =>
+        s"openat $fileName: path escapes from parent"
+      case e: InvalidPathException     => s"openat $fileName: ${e.getMessage}"
+      case e: IllegalArgumentException => s"openat $fileName: ${e.getMessage}"
+      case e                           => e.toString
+    }
+
   private def writeFile(
       config: Config,
       f: os.Path,
@@ -692,7 +706,7 @@ object SjsonnetMainBase {
                     ujson.transform(v, renderer)
                     writer.toString
                   }
-                  relPath = (os.FilePath(multiPath) / os.RelPath(f)).asInstanceOf[os.FilePath]
+                  relPath <- multiOutputPath(multiPath, f)
                   _ <- writeFile(config, relPath.resolveFrom(wd), rendered, trailingNewline)
                 } yield relPath
               }

sjsonnet/test/src-jvm/sjsonnet/MainTests.scala

@@ -299,6 +299,59 @@ object MainTests extends TestSuite {
       assert(os.read(multiDest / "world") == expectedWorld + "\n")
     }
 
+    test("multiRejectsOutputPathsEscapingParent") {
+      val root = os.temp.dir()
+      val multiDest = root / "out"
+      val (res, out, err) =
+        runMain("""{"../escape.txt": "owned"}""", "--exec", "--multi", multiDest, "--string")
+      assert(res == 1)
+      assert(out.isEmpty)
+      assert(err.contains("path escapes from parent"))
+      assert(!err.contains("IllegalArgumentException"))
+      assert(!os.exists(root / "escape.txt"))
+    }
+
+    test("multiRejectsNestedOutputPathsEscapingParent") {
+      val root = os.temp.dir()
+      val multiDest = root / "out"
+      val (res, out, err) =
+        runMain("""{"a/../../escape.txt": "owned"}""", "--exec", "--multi", multiDest, "--string")
+      assert(res == 1)
+      assert(out.isEmpty)
+      assert(err.contains("path escapes from parent"))
+      assert(!err.contains("IllegalArgumentException"))
+      assert(!os.exists(root / "escape.txt"))
+    }
+
+    test("multiAllowsNormalizedOutputPathsInsideParent") {
+      val root = os.temp.dir()
+      val multiDest = root / "out"
+      os.makeDir.all(multiDest)
+      val (res, out, err) =
+        runMain("""{"dir/../ok.txt": "ok"}""", "--exec", "--multi", multiDest, "--string")
+      assert((res, out, err) == ((0, s"$multiDest/ok.txt\n", "")))
+      assert(os.read(multiDest / "ok.txt") == "ok\n")
+    }
+
+    test("multiNormalizesAbsoluteOutputPathsInsideParent") {
+      val root = os.temp.dir()
+      val multiDest = root / "out"
+      val externalPath = root / "external" / "abs.txt"
+      val expectedPath = multiDest / os.SubPath(externalPath.toString.dropWhile(_ == '/'))
+      val (res, out, err) =
+        runMain(
+          "{" + ujson.write(externalPath.toString) + ": \"inside\"}",
+          "--exec",
+          "--multi",
+          multiDest,
+          "--string",
+          "--create-output-dirs"
+        )
+      assert((res, out, err) == ((0, s"$expectedPath\n", "")))
+      assert(os.read(expectedPath) == "inside\n")
+      assert(!os.exists(externalPath))
+    }
+
     test("missingExtStrFileErrorsAsImport") {
       checkCliStderrGolden(
         "cli_missing_ext_str_file.jsonnet",