ppp: improve LCP magic number negotiation

2 files changed, 41 insertions, 8 deletions

diff --git a/accel-pppd/ppp/lcp_opt_magic.c b/accel-pppd/ppp/lcp_opt_magic.c
index 81eadd6d..e2d9bade 100644
--- a/accel-pppd/ppp/lcp_opt_magic.c
+++ b/accel-pppd/ppp/lcp_opt_magic.c
@@ -14,7 +14,8 @@ static int magic_send_conf_req(struct ppp_lcp_t *lcp, struct lcp_option_t *opt,
 static int magic_send_conf_nak(struct ppp_lcp_t *lcp, struct lcp_option_t *opt, uint8_t *ptr);
 static int magic_recv_conf_req(struct ppp_lcp_t *lcp, struct lcp_option_t *opt, uint8_t *ptr);
 static int magic_recv_conf_rej(struct ppp_lcp_t *lcp, struct lcp_option_t *opt, uint8_t *ptr);
-static void magic_print(void (*print)(const char *fmt,...),struct lcp_option_t*, uint8_t *ptr);
+static int magic_recv_conf_nak(struct ppp_lcp_t *lcp, struct lcp_option_t *opt, uint8_t *ptr);
+static void magic_print(void (*print)(const char *fmt, ...), struct lcp_option_t*, uint8_t *ptr);
 
 struct magic_option_t
 {
@@ -29,15 +30,28 @@ static struct lcp_option_handler_t magic_opt_hnd=
 	.send_conf_nak = magic_send_conf_nak,
 	.recv_conf_req = magic_recv_conf_req,
 	.recv_conf_rej = magic_recv_conf_rej,
+	.recv_conf_nak = magic_recv_conf_nak,
 	.free = magic_free,
 	.print = magic_print,
 };
 
+static int nzmagic(int old)
+{
+	int magic;
+
+	do {
+		magic = random();
+	} while (magic == old || !magic);
+
+	return magic;
+}
+
 static struct lcp_option_t *magic_init(struct ppp_lcp_t *lcp)
 {
 	struct magic_option_t *magic_opt = _malloc(sizeof(*magic_opt));
+
 	memset(magic_opt, 0, sizeof(*magic_opt));
-	do { magic_opt->magic = random(); } while (magic_opt->magic == 0);
+	magic_opt->magic = nzmagic(0);
 	magic_opt->opt.id = CI_MAGIC;
 	magic_opt->opt.len = 6;
 
@@ -71,9 +85,10 @@ static int magic_send_conf_nak(struct ppp_lcp_t *lcp, struct lcp_option_t *opt,
 {
 	struct magic_option_t *magic_opt = container_of(opt, typeof(*magic_opt), opt);
 	struct lcp_opt32_t *opt32 = (struct lcp_opt32_t *)ptr;
+
 	opt32->hdr.id = CI_MAGIC;
 	opt32->hdr.len = 6;
-	do { opt32->val = random(); } while (opt32->val == magic_opt->magic);
+	opt32->val = htonl(nzmagic(magic_opt->magic));
 	return 6;
 }
 
@@ -84,11 +99,11 @@ static int magic_recv_conf_req(struct ppp_lcp_t *lcp, struct lcp_option_t *opt,
 
 	/*if (!ptr)
 		return LCP_OPT_NAK;*/
-	
+
 	if (opt32->hdr.len != 6)
 		return LCP_OPT_REJ;
 
-	if (magic_opt->magic == ntohl(opt32->val))
+	if (magic_opt->magic && magic_opt->magic == ntohl(opt32->val))
 		return LCP_OPT_NAK;
 
 	return LCP_OPT_ACK;
@@ -97,14 +112,32 @@ static int magic_recv_conf_req(struct ppp_lcp_t *lcp, struct lcp_option_t *opt,
 static int magic_recv_conf_rej(struct ppp_lcp_t *lcp, struct lcp_option_t *opt, uint8_t *ptr)
 {
 	struct magic_option_t *magic_opt = container_of(opt, typeof(*magic_opt), opt);
-	
+
 	magic_opt->magic = 0;
 	lcp->magic = 0;
 
 	return 0;
 }
 
-static void magic_print(void (*print)(const char *fmt,...),struct lcp_option_t *opt, uint8_t *ptr)
+static int magic_recv_conf_nak(struct ppp_lcp_t *lcp, struct lcp_option_t *opt, uint8_t *ptr)
+{
+	struct magic_option_t *magic_opt = container_of(opt, typeof(*magic_opt), opt);
+	struct lcp_opt32_t *opt32 = (struct lcp_opt32_t *)ptr;
+
+	if (opt32->hdr.len != 6)
+		return -1;
+
+	/* Loop-back detected */
+	if (magic_opt->magic && magic_opt->magic == ntohl(opt32->val))
+		return -1;
+
+	magic_opt->magic = ntohl(opt32->val) ? : nzmagic(magic_opt->magic);
+	lcp->magic = magic_opt->magic;
+
+	return 0;
+}
+
+static void magic_print(void (*print)(const char *fmt, ...), struct lcp_option_t *opt, uint8_t *ptr)
 {
 	struct magic_option_t *magic_opt = container_of(opt, typeof(*magic_opt), opt);
 	struct lcp_opt32_t *opt32 = (struct lcp_opt32_t *)ptr;
diff --git a/accel-pppd/ppp/ppp_lcp.c b/accel-pppd/ppp/ppp_lcp.c
index 5975d5db..54826efc 100644
--- a/accel-pppd/ppp/ppp_lcp.c
+++ b/accel-pppd/ppp/ppp_lcp.c
@@ -609,7 +609,7 @@ static void lcp_recv_echo_repl(struct ppp_lcp_t *lcp, uint8_t *data, int size)
 		if (conf_ppp_verbose)
 			log_ppp_debug("recv [LCP EchoRep id=%x <magic %08x>]\n", lcp->fsm.recv_id, magic);
 
-		if (magic == lcp->magic) {
+		if (lcp->magic && magic == lcp->magic) {
 			log_ppp_error("lcp: echo: loop-back detected\n");
 			ap_session_terminate(&lcp->ppp->ses, TERM_NAS_ERROR, 0);
 		}