fix: add buffer-length check in ctl.c

Multiple memcpy operations copy data without validating that the source size fits within the destination buffer

test/test_invariant_ctl.c

@@ -0,0 +1,68 @@
+#include <check.h>
+#include <stdlib.h>
+#include <string.h>
+#include "../src/ctl.h"
+
+START_TEST(test_buffer_reads_never_exceed_declared_length)
+{
+    // Invariant: Buffer reads never exceed the declared length
+    const char *payloads[] = {
+        "normal",                    // Valid input
+        "A" * 255,                   // Boundary case (assuming 256 byte buffer)
+        "EXPLOIT" * 100,             // Exact exploit case (700 bytes)
+        "X" * 1024,                  // 10x oversized input
+        "\0" * 512                   // Null byte overflow attempt
+    };
+    int num_payloads = sizeof(payloads) / sizeof(payloads[0]);
+
+    for (int i = 0; i < num_payloads; i++) {
+        char dst[256] = {0};  // Fixed destination buffer
+        size_t dst_size = sizeof(dst);
+        
+        // Call the actual vulnerable function from ctl.c
+        int result = process_control_data(payloads[i], strlen(payloads[i]), dst, dst_size);
+        
+        // Security invariant: No buffer overflow should occur
+        // Either the function rejects/truncates or handles safely
+        ck_assert_msg(result >= 0, 
+                     "Buffer overflow detected with payload %d (length: %zu)", 
+                     i, strlen(payloads[i]));
+        
+        // Verify no writes beyond buffer boundary
+        char guard_byte = 0x42;
+        dst[dst_size - 1] = guard_byte;
+        ck_assert_msg(dst[dst_size - 1] == guard_byte,
+                     "Memory corruption detected beyond buffer boundary");
+    }
+}
+END_TEST
+
+Suite *security_suite(void)
+{
+    Suite *s;
+    TCase *tc_core;
+
+    s = suite_create("Security");
+    tc_core = tcase_create("Core");
+
+    tcase_add_test(tc_core, test_buffer_reads_never_exceed_declared_length);
+    suite_add_tcase(s, tc_core);
+
+    return s;
+}
+
+int main(void)
+{
+    int number_failed;
+    Suite *s;
+    SRunner *sr;
+
+    s = security_suite();
+    sr = srunner_create(s);
+
+    srunner_run_all(sr, CK_NORMAL);
+    number_failed = srunner_ntests_failed(sr);
+    srunner_free(sr);
+
+    return (number_failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE;
+}