tests: cover additional safeguards and document PR 40 comparison

Add standalone regression coverage for DHCPv6 parsing/replies, RADIUS
response authentication/signing, VRF/CoA name bounds, LCP Echo MTU and
pool reuse. Document all 20 reference commits, upstream coverage, author
credits, adaptations and validation limits.

Validation: default userspace Debug build; five standalone suites with
ASan/UBSan (LCP UBSan only), including LeakSanitizer for ASan tests;
existing IPv6 DNS test; git diff --check. All passed.
Baseline duplicate Rapid-Commit and forged Access-Accept assertions fail
as expected. Full privileged session integration was not run.

1 files changed, 72 insertions, 0 deletions

diff --git a/tests/unit/vrf_safeguards_test.c b/tests/unit/vrf_safeguards_test.c
new file mode 100644
index 00000000..1fa5a414
--- /dev/null
+++ b/tests/unit/vrf_safeguards_test.c
@@ -0,0 +1,72 @@
+/* Exercise the shared interface lookup and length-delimited VRF API. */
+#include <assert.h>
+#include <pthread.h>
+#include "triton.h"
+#undef DEFINE_INIT
+#undef __init
+#define __init
+#define DEFINE_INIT(o, f)
+#include "../../accel-pppd/net.c"
+#include "../../accel-pppd/ifcfg.c"
+#define init coa_init
+#include "../../accel-pppd/radius/dm_coa.c"
+#undef init
+
+static int lookups, changes, last_master;
+static char last_name[IFNAMSIZ];
+void log_ppp_error(const char *fmt, ...) {}
+void log_ppp_info2(const char *fmt, ...) {}
+
+static int lookup(const char *name)
+{
+	lookups++;
+	assert(strlen(name) < IFNAMSIZ);
+	strcpy(last_name, name);
+	return 7;
+}
+static int set_vrf(int index, int master)
+{
+	changes++;
+	last_master = master;
+	return 0;
+}
+
+int main(void)
+{
+	struct kern_net kn = {0};
+	struct ap_net backend = {.get_ifindex = lookup, .set_vrf = set_vrf};
+	struct ap_session ses = {.net = &backend};
+	struct radius_pd_t rpd = {.ses = &ses};
+	char name[IFNAMSIZ + 1];
+
+	net = &kn.net;
+	kn.sock = socket(AF_INET, SOCK_DGRAM, 0);
+	assert(kn.sock >= 0);
+	assert(def_get_ifindex("lo") > 0);
+	assert(def_get_ifindex(NULL) == -1);
+	memset(name, 'x', sizeof(name));
+	name[IFNAMSIZ] = 0;
+	assert(def_get_ifindex(name) == -1);
+	assert(ap_session_vrf(&ses, name, -1) == -1);
+	assert(ap_session_vrf(&ses, name, IFNAMSIZ) == -1);
+	assert(ap_session_vrf(&ses, NULL, 1) == -1);
+	assert(ap_session_vrf(&ses, name, -2) == -1);
+	assert(ap_session_vrf(&ses, "a\0b", 3) == -1);
+	assert(!lookups && !changes);
+	/* Explicit length need not be followed by a NUL in caller memory. */
+	assert(!ap_session_vrf(&ses, name, IFNAMSIZ - 1));
+	assert(strlen(last_name) == IFNAMSIZ - 1 && last_master == 7);
+	assert(!ap_session_vrf(&ses, NULL, 0));
+	assert(last_master == 0 && !ses.vrf_name);
+	assert(!ap_session_vrf(&ses, NULL, -1));
+	assert(lookups == 1 && changes == 3);
+	assert(!rad_update_vrf(&rpd, "blue\0junk", 9));
+	assert(!rad_update_vrf(&rpd, name, IFNAMSIZ));
+	assert(rad_update_vrf(&rpd, "0", 1));
+	assert(last_master == 0);
+	assert(rad_update_vrf(&rpd, "0blue", 5));
+	assert(last_master == 7 && !strcmp(last_name, "0blue"));
+	close(kn.sock);
+	puts("VRF safeguards: PASS");
+	return 0;
+}