Stop reading printf templates at the size limit

rhash_main.c

@@ -169,11 +169,12 @@ static int load_printf_template(void)
 		len = fread(buffer, 1, 8192, fd);
 		if (ferror(fd)) break;
 
-		rsh_str_append_n(rhash_data.template_text, buffer, len);
-		if (rhash_data.template_text->len >= MAX_TEMPLATE_SIZE) {
+		if (len >= MAX_TEMPLATE_SIZE - rhash_data.template_text->len) {
 			log_msg_file_t(_("%s: template file is too big\n"), &file);
 			error = 1;
+			break;
 		}
+		rsh_str_append_n(rhash_data.template_text, buffer, len);
 	}
 
 	if (ferror(fd)) {

tests/test_template_limit.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+import os
+from pathlib import Path
+import subprocess
+import sys
+import tempfile
+
+binary = str(Path(sys.argv[1]).resolve())
+with tempfile.TemporaryDirectory() as directory:
+    template = Path(directory, "template.fmt")
+    os.mkfifo(template)
+    process = subprocess.Popen([binary, f"--template={template}", "--message=abc"],
+                               cwd=directory, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                               text=True)
+    with template.open("wb", buffering=0) as writer:
+        try:
+            writer.write(b"x" * 65536)
+        except BrokenPipeError:
+            pass
+        try:
+            stdout, stderr = process.communicate(timeout=2)
+        except subprocess.TimeoutExpired:
+            process.kill()
+            stdout, stderr = process.communicate()
+            raise AssertionError("RHash kept reading the template after the size limit")
+    assert process.returncode == 2, (process.returncode, stdout, stderr)
+    assert "template file is too big" in stderr, stderr
+print("PASS: template loading stops at the configured size limit")