From: Matthieu Hautreux <[email protected]> One major drawback of DHCP over IB is the requirement to use broadcasted replies. The only way for a IB dhclient to find its own reply is by looking for matching xid (transaction ID). xid are generated using random() in dhclient. random() is initialized using srandom(seed+cur_time). Nethertheless, when hw address hlen is 1, the processed seed is roughly always the same. As a result, IB nodes that uses dhclient to configure IB interfaces at the same time share the same xid and as a result use any of the broadcasted replies. The protocol is then broken.
The proposed patch build a "backup seed" using all the interfaces available on the machine and use it if it can not find a good seed for the required interfaces during real DHCP process. If backup seed construction fails (no interfaces providing a hw address long enough for seed construction), it try to build a seed using gethostid(). Signed-off-by: Sebastien Dugue <[email protected]> dhclient.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 53 insertions(+), 11 deletions(-) Index: dhcp-4.1.0p1/client/dhclient.c =================================================================== --- dhcp-4.1.0p1.orig/client/dhclient.c 2010-05-17 16:03:33.000000000 +0200 +++ dhcp-4.1.0p1/client/dhclient.c 2010-05-17 16:04:08.000000000 +0200 @@ -906,6 +906,26 @@ } } + /* We create a backup seed before rediscovering interfaces in order to + have a seed built using all of the available interfaces + It's interesting if required interfaces doesn't let us defined + a really unique seed due to a lack of valid HW addr later + (this is the case with DHCP over IB) + We only use the last device as using a sum could broke the + uniqueness of the seed among multiple nodes + */ + unsigned backup_seed = 0; + for (ip = interfaces; ip; ip = ip -> next) { + int junk; + if ( ip -> hw_address.hlen <= sizeof seed ) + continue; + memcpy (&junk, + &ip -> hw_address.hbuf [ip -> hw_address.hlen - + sizeof seed], sizeof seed); + backup_seed = junk; + } + + /* At this point, all the interfaces that the script thinks are relevant should be running, so now we once again call discover_interfaces(), and this time ask it to actually set @@ -920,14 +940,36 @@ Not much entropy, but we're booting, so we're not likely to find anything better. */ seed = 0; + int seed_flag = 0; for (ip = interfaces; ip; ip = ip->next) { int junk; + if ( ip -> hw_address.hlen <= sizeof seed ) + continue; memcpy(&junk, &ip->hw_address.hbuf[ip->hw_address.hlen - sizeof seed], sizeof seed); seed += junk; + seed_flag = 1; } - srandom(seed + cur_time); + if ( seed_flag == 0 ) { + if ( backup_seed != 0 ) { + seed = backup_seed; + log_info ("xid: rand init seed (%u) built using all" + " available interfaces",seed); + } + else { + seed = cur_time^((unsigned) gethostid()) ; + log_info ("xid: warning: no netdev with useable HWADDR found" + " for seed's uniqueness enforcement"); + log_info ("xid: rand init seed (%u) built using gethostid", + seed); + } + /* we only use seed and no current time as a broadcast reply */ + /* will certainly be used by the hwaddrless interface */ + srandom(seed); + } + else + srandom(seed + cur_time); /* Setup specific Infiniband options */ for (ip = interfaces; ip; ip = ip->next) { @@ -1423,7 +1465,7 @@ return; } - log_info ("DHCPACK from %s", piaddr (packet -> client_addr)); + log_info ("DHCPACK from %s (xid=%u)", piaddr (packet -> client_addr), client -> xid); lease = packet_to_lease (packet, client); if (!lease) { @@ -2123,7 +2165,7 @@ return; } - log_info ("DHCPNAK from %s", piaddr (packet -> client_addr)); + log_info ("DHCPNAK from %s (xid=%u)", piaddr (packet -> client_addr), client -> xid); if (!client -> active) { #if defined (DEBUG) @@ -2249,10 +2291,10 @@ client -> packet.secs = htons (65535); client -> secs = client -> packet.secs; - log_info ("DHCPDISCOVER on %s to %s port %d interval %ld", + log_info ("DHCPDISCOVER on %s to %s port %d interval %ld (xid=%u)", client -> name ? client -> name : client -> interface -> name, inet_ntoa (sockaddr_broadcast.sin_addr), - ntohs (sockaddr_broadcast.sin_port), (long)(client -> interval)); + ntohs (sockaddr_broadcast.sin_port), (long)(client -> interval), client -> xid); /* Send out a packet. */ result = send_packet (client -> interface, (struct packet *)0, @@ -2524,10 +2566,10 @@ client -> packet.secs = htons (65535); } - log_info ("DHCPREQUEST on %s to %s port %d", + log_info ("DHCPREQUEST on %s to %s port %d (xid=%u)", client -> name ? client -> name : client -> interface -> name, inet_ntoa (destination.sin_addr), - ntohs (destination.sin_port)); + ntohs (destination.sin_port), client -> xid); if (destination.sin_addr.s_addr != INADDR_BROADCAST && fallback_interface) @@ -2557,10 +2599,10 @@ int result; - log_info ("DHCPDECLINE on %s to %s port %d", + log_info ("DHCPDECLINE on %s to %s port %d (xid=%u)", client -> name ? client -> name : client -> interface -> name, inet_ntoa (sockaddr_broadcast.sin_addr), - ntohs (sockaddr_broadcast.sin_port)); + ntohs (sockaddr_broadcast.sin_port), client -> xid); /* Send out a packet. */ result = send_packet (client -> interface, (struct packet *)0, @@ -2600,10 +2642,10 @@ return; } - log_info ("DHCPRELEASE on %s to %s port %d", + log_info ("DHCPRELEASE on %s to %s port %d (xid=%u)", client -> name ? client -> name : client -> interface -> name, inet_ntoa (destination.sin_addr), - ntohs (destination.sin_port)); + ntohs (destination.sin_port), client -> xid); if (fallback_interface) result = send_packet (fallback_interface, _______________________________________________ ewg mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg
