The situation is this: Two programs have opened IPv4 UDP sockets, set SO_REUSEADDR on them, and are bound to INADDR_ANY on the same port. One program joins a multicast group address, the other program joins a different one. When a multicast packet is sent to this port on one of the group addresses to which these sockets are bound, both sockets get delivered a copy of the packet. Only the socket that is bound to the group address to which the packet was sent should get it.
The issue seems to be that there is no actual check to see if the socket is joined to the multicast group. This patch adds such a check, and corrected the problem on my test rig. I looked briefly at the ipv6 equivalent code, and it appears to already handle this correctly with a check near the top of inet6_mc_check(). I have not actually verified this, however. This patch should apply cleanly to Linus' git tree as of last night. Signed-off-by: Jeff Layton <[EMAIL PROTECTED]> --- linux-2.6/net/ipv4/udp.c.mcast-filter +++ linux-2.6/net/ipv4/udp.c @@ -286,6 +286,8 @@ static inline struct sock *udp_v4_mcast_ struct hlist_node *node; struct sock *s = sk; unsigned short hnum = ntohs(loc_port); + struct ip_mc_socklist *mc_list; + int matched; sk_for_each_from(s, node) { struct inet_sock *inet = inet_sk(s); @@ -299,6 +301,23 @@ static inline struct sock *udp_v4_mcast_ continue; if (!ip_mc_sf_allow(s, loc_addr, rmt_addr, dif)) continue; + + /* only deliver multicast packets to sockets that are + * explicitly joined to the multicast group */ + if (MULTICAST(loc_addr)) { + matched = 0; + for (mc_list=inet->mc_list ; mc_list; + mc_list=mc_list->next) { + if (mc_list->multi.imr_multiaddr.s_addr == + loc_addr) { + matched = 1; + break; + } + } + if (!matched) + continue; + } + goto found; } s = NULL; - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html