RA: Warn if advertised MTU is greater than link MTU

diff --git a/src/ipv6nd.c b/src/ipv6nd.c
index 3cf697136a1c0f7dd87b0c8c9686bb59cde0af39..6033ee11bb47a098fac9bdfb19ea51cdb486ea71 100644 (file)
--- a/src/ipv6nd.c
+++ b/src/ipv6nd.c
@@ -990,6 +990,7 @@ ipv6nd_handlera(struct dhcpcd_ctx *ctx,
        struct dhcp_opt *dho;
        bool new_rap, new_data, has_address;
        uint32_t old_lifetime;
+       int ifmtu;
        __printflike(1, 2) void (*logfunc)(const char *, ...);
 #ifdef IPV6_MANAGETEMPADDR
        uint8_t new_ap;
@@ -1274,22 +1275,30 @@ ipv6nd_handlera(struct dhcpcd_ctx *ctx,
 
                case ND_OPT_MTU:
                        if (len < sizeof(mtu)) {
-                               logerrx("%s: short MTU option", ifp->name);
+                               logfunc("%s: short MTU option", ifp->name);
                                break;
                        }
                        memcpy(&mtu, p, sizeof(mtu));
                        mtu.nd_opt_mtu_mtu = ntohl(mtu.nd_opt_mtu_mtu);
                        if (mtu.nd_opt_mtu_mtu < IPV6_MMTU) {
-                               logerrx("%s: invalid MTU %d",
+                               logfunc("%s: invalid MTU %d",
                                    ifp->name, mtu.nd_opt_mtu_mtu);
                                break;
                        }
-                       rap->mtu = mtu.nd_opt_mtu_mtu;
+                       ifmtu = if_getmtu(ifp);
+                       if (ifmtu == -1)
+                               logerr("if_getmtu");
+                       else if (mtu.nd_opt_mtu_mtu > (uint32_t)ifmtu) {
+                               logfunc("%s: advertised MTU %d"
+                                   " is greater than link MTU %d",
+                                   ifp->name, mtu.nd_opt_mtu_mtu, ifmtu);
+                               rap->mtu = (uint32_t)ifmtu;
+                       } else
+                               rap->mtu = mtu.nd_opt_mtu_mtu;
                        break;
-
                case ND_OPT_RDNSS:
                        if (len < sizeof(rdnss)) {
-                               logerrx("%s: short RDNSS option", ifp->name);
+                               logfunc("%s: short RDNSS option", ifp->name);
                                break;
                        }
                        memcpy(&rdnss, p, sizeof(rdnss));