From c0fbc7ef2ae2919bf6162b4149d341f448289836 Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Mon, 25 Nov 2024 00:52:57 +0100 Subject: dhcp: Honour broadcast flag (RFC 2131, 4.1) It's widely considered a legacy option nowadays, and I've haven't seen clients setting it since Windows 95, but it's convenient for a minimal DHCP client not using raw IP sockets such as what I'm playing with for muvm. Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- dhcp.c | 12 ++++++++++-- ip.h | 3 +++ 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/dhcp.c b/dhcp.c index a16cde8..d8515aa 100644 --- a/dhcp.c +++ b/dhcp.c @@ -112,6 +112,8 @@ struct msg { uint32_t xid; uint16_t secs; uint16_t flags; +#define FLAG_BROADCAST htons_constant(0x8000) + uint32_t ciaddr; struct in_addr yiaddr; uint32_t siaddr; @@ -285,10 +287,10 @@ int dhcp(const struct ctx *c, const struct pool *p) { size_t mlen, dlen, offset = 0, opt_len, opt_off = 0; char macstr[ETH_ADDRSTRLEN]; + struct in_addr mask, dst; const struct ethhdr *eh; const struct iphdr *iph; const struct udphdr *uh; - struct in_addr mask; unsigned int i; struct msg *m; @@ -400,7 +402,13 @@ int dhcp(const struct ctx *c, const struct pool *p) opt_set_dns_search(c, sizeof(m->o)); dlen = offsetof(struct msg, o) + fill(m); - tap_udp4_send(c, c->ip4.our_tap_addr, 67, c->ip4.addr, 68, m, dlen); + + if (m->flags & FLAG_BROADCAST) + dst = in4addr_broadcast; + else + dst = c->ip4.addr; + + tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, m, dlen); return 1; } diff --git a/ip.h b/ip.h index 0742612..1544dbf 100644 --- a/ip.h +++ b/ip.h @@ -101,4 +101,7 @@ static const struct in6_addr in6addr_ll_all_nodes = { }, }; +/* IPv4 Limited Broadcast (RFC 919, Section 7), 255.255.255.255 */ +static const struct in_addr in4addr_broadcast = { 0xffffffff }; + #endif /* IP_H */ -- cgit v1.2.3