4 files changed, 28 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index fbe427a6580c..a0e134dd2523 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1086,6 +1086,24 @@ accept_dad - INTEGER
         2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
            link-local address has been found.
 
+force_tllao - BOOLEAN
+        Enable sending the target link-layer address option even when
+        responding to a unicast neighbor solicitation.
+        Default: FALSE
+
+        Quoting from RFC 2461, section 4.4, Target link-layer address:
+
+        "The option MUST be included for multicast solicitations in order to
+        avoid infinite Neighbor Solicitation "recursion" when the peer node
+        does not have a cache entry to return a Neighbor Advertisements
+        message.  When responding to unicast solicitations, the option can be
+        omitted since the sender of the solicitation has the correct link-
+        layer address; otherwise it would not have be able to send the unicast
+        solicitation in the first place. However, including the link-layer
+        address in this case adds little overhead and eliminates a potential
+        race condition where the sender deletes the cached link-layer address
+        prior to receiving a response to a previous solicitation."
+
 icmp/*:
 ratelimit - INTEGER
         Limit the maximal rates for sending ICMPv6 packets.
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index c662efa68289..ae74ede1abe7 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -167,6 +167,7 @@ struct ipv6_devconf {
 #endif
         __s32           disable_ipv6;
         __s32           accept_dad;
+        __s32           force_tllao;
         void            *sysctl;
 };
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 1fd0a3d775d2..bdcee6981c60 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4353,6 +4353,14 @@ static struct addrconf_sysctl_table
                         .proc_handler   =       proc_dointvec,
                 },
                 {
+                        .ctl_name       = CTL_UNNUMBERED,
+                        .procname       = "force_tllao",
+                        .data           = &ipv6_devconf.force_tllao,
+                        .maxlen         = sizeof(int),
+                        .mode           = 0644,
+                        .proc_handler   = proc_dointvec
+                },
+                {
                         .ctl_name       =       0,      /* sentinel */
                 }
         },
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index f74e4e2cdd06..3507cfe1e7a2 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -598,6 +598,7 @@ static void ndisc_send_na(struct net_device *dev, struct neighbour *neigh,
         icmp6h.icmp6_solicited = solicited;
         icmp6h.icmp6_override = override;
 
+        inc_opt |= ifp->idev->cnf.force_tllao;
         __ndisc_send(dev, neigh, daddr, src_addr,
                      &icmp6h, solicited_addr,
                      inc_opt ? ND_OPT_TARGET_LL_ADDR : 0);