diff options
| author | Michael Brown <mcb30@ipxe.org> | 2024-06-26 04:29:38 -0700 |
|---|---|---|
| committer | Michael Brown <mcb30@ipxe.org> | 2024-06-26 05:01:58 -0700 |
| commit | 77acf6b41f705384593a057c2bea057283bf429b (patch) | |
| tree | 1605971b7759d8f81964576dd92d0657efbd37a6 /src/net/ipv4.c | |
| parent | 821bb326f87fbc000376fdc5371e9e53f666267a (diff) | |
| download | ipxe-77acf6b41f705384593a057c2bea057283bf429b.tar.gz | |
[ipv4] Support small subnets with no directed broadcast address
In a small subnet (with a /31 or /32 subnet mask), all addresses
within the subnet are valid host addresses: there is no separate
network address or directed broadcast address.
The logic used in iPXE to determine whether or not to use a link-layer
broadcast address will currently fail in these subnets. In a /31
subnet, the higher of the two host addresses (i.e. the address with
all host bits set) will be treated as a broadcast address. In a /32
subnet, the single valid host address will be treated as a broadcast
address.
Fix by adding the concept of a host mask, defined such that an address
in the local subnet with all of the mask bits set to zero represents
the network address, and an address in the local subnet with all of
the mask bits set to one represents the directed broadcast address.
For most subnets, this is simply the inverse of the subnet mask. For
small subnets (/31 or /32) we can obtain the desired behaviour by
setting the host mask to all ones, so that only the local broadcast
address 255.255.255.255 will be treated as a broadcast address.
Originally-fixed-by: Lukas Stockner <lstockner@genesiscloud.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Diffstat (limited to 'src/net/ipv4.c')
| -rw-r--r-- | src/net/ipv4.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/src/net/ipv4.c b/src/net/ipv4.c index b91fa2ad0..5d0cb0f9a 100644 --- a/src/net/ipv4.c +++ b/src/net/ipv4.c @@ -85,9 +85,18 @@ static int add_ipv4_miniroute ( struct net_device *netdev, struct in_addr address, struct in_addr netmask, struct in_addr gateway ) { struct ipv4_miniroute *miniroute; + struct in_addr hostmask; + struct in_addr broadcast; + /* Calculate host mask */ + hostmask.s_addr = ( IN_IS_SMALL ( netmask.s_addr ) ? + INADDR_NONE : ~netmask.s_addr ); + broadcast.s_addr = ( address.s_addr | hostmask.s_addr ); + + /* Print debugging information */ DBGC ( netdev, "IPv4 add %s", inet_ntoa ( address ) ); DBGC ( netdev, "/%s ", inet_ntoa ( netmask ) ); + DBGC ( netdev, "bc %s ", inet_ntoa ( broadcast ) ); if ( gateway.s_addr ) DBGC ( netdev, "gw %s ", inet_ntoa ( gateway ) ); DBGC ( netdev, "via %s\n", netdev->name ); @@ -103,8 +112,9 @@ static int add_ipv4_miniroute ( struct net_device *netdev, miniroute->netdev = netdev_get ( netdev ); miniroute->address = address; miniroute->netmask = netmask; + miniroute->hostmask = hostmask; miniroute->gateway = gateway; - + /* Add to end of list if we have a gateway, otherwise * to start of list. */ @@ -310,7 +320,7 @@ static int ipv4_tx ( struct io_buffer *iobuf, struct sockaddr_in *sin_dest = ( ( struct sockaddr_in * ) st_dest ); struct ipv4_miniroute *miniroute; struct in_addr next_hop; - struct in_addr netmask = { .s_addr = 0 }; + struct in_addr hostmask = { .s_addr = INADDR_NONE }; uint8_t ll_dest_buf[MAX_LL_ADDR_LEN]; const void *ll_dest; int rc; @@ -338,7 +348,7 @@ static int ipv4_tx ( struct io_buffer *iobuf, ( ( miniroute = ipv4_route ( sin_dest->sin_scope_id, &next_hop ) ) != NULL ) ) { iphdr->src = miniroute->address; - netmask = miniroute->netmask; + hostmask = miniroute->hostmask; netdev = miniroute->netdev; } if ( ! netdev ) { @@ -373,7 +383,7 @@ static int ipv4_tx ( struct io_buffer *iobuf, ntohs ( iphdr->chksum ) ); /* Calculate link-layer destination address, if possible */ - if ( ( ( next_hop.s_addr ^ INADDR_BROADCAST ) & ~netmask.s_addr ) == 0){ + if ( ( ( ~next_hop.s_addr ) & hostmask.s_addr ) == 0 ) { /* Broadcast address */ ipv4_stats.out_bcast_pkts++; ll_dest = netdev->ll_broadcast; |