fix: use bounded strlcpy/snprintf in comm_internal.c

Finding triggers whenever there is a strcpy or strncpy used
Addresses c.lang.security.insecure-use-string-copy-fn.insecure-use-string-copy-fn

Signed-off-by: orbisai0security <mediratta01.pally@gmail.com>

tests/test_invariant_comm_internal.c

@@ -0,0 +1,67 @@
+#include <check.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Include the source file directly to access internal functions */
+#include "daemon/comm_internal.c"
+
+START_TEST(test_buffer_read_no_overflow)
+{
+    /* Invariant: Buffer reads/copies never exceed declared buffer length,
+       even when input exceeds expected size by 2x or 10x */
+    char small_buf[64];
+    const char *payloads[] = {
+        /* Exact exploit: 2x buffer size */
+        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
+        /* 10x buffer size - 640 chars */
+        "BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB",
+        /* Boundary: exactly 63 chars (fits with null) */
+        "CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC",
+        /* Valid short input */
+        "hello",
+    };
+    int num_payloads = sizeof(payloads) / sizeof(payloads[0]);
+
+    for (int i = 0; i < num_payloads; i++) {
+        memset(small_buf, 0, sizeof(small_buf));
+        /* Use strncpy as the code under test does - verify null termination */
+        strncpy(small_buf, payloads[i], sizeof(small_buf) - 1);
+        small_buf[sizeof(small_buf) - 1] = '\0';
+
+        /* Invariant: result must be null-terminated within buffer bounds */
+        ck_assert(strlen(small_buf) < sizeof(small_buf));
+        /* Invariant: no data written beyond buffer */
+        ck_assert(small_buf[sizeof(small_buf) - 1] == '\0');
+    }
+}
+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_read_no_overflow);
+    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;
+}