[PATCH v4 0/3] dhcp: Add support for Rapid Commit, broadcast replies

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Stefano Brivio

26 Nov 2024 26 Nov '24

7:34 a.m.

These are all changes coming from pending muvm experiments where I'm trying to speed up and simplify the networking setup in the guest. v4: In 1/3, don't swap the "BOOTP" and "DHCP" labels: we want to print "BOOTP" if option 53 isn't there or has zero length, not the other way around. Further, check that clen for option 53 is > 0 before checking if it's a DHCPDISCOVER. Given that DHCPDISCOVER is 1 (not 0), this happened to already work for BOOTP, but it worked by mistake v3: In 1/3, set 'slen' for options we won't send to -1 in dhcp_init(), and reset it for option 80 every time we handle a DHCP request. Add a comment about DHCP needing a valid message type (option 53) v2: In 3/3, add in4addr_broadcast to ip.h, instead of open-coding it in dhcp() Stefano Brivio (3): dhcp: Use -1 as "missing option" length instead of 0 dhcp: Introduce support for Rapid Commit (option 80, RFC 4039) dhcp: Honour broadcast flag (RFC 2131, 4.1) dhcp.c | 53 +++++++++++++++++++++++++++++++++++++++++------------ ip.h | 3 +++ 2 files changed, 44 insertions(+), 12 deletions(-) -- 2.43.0

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Stefano Brivio

26 Nov 26 Nov

7:34 a.m.

New subject: [PATCH v4 1/3] dhcp: Use -1 as "missing option" length instead of 0

We want to add support for option 80 (Rapid Commit, RFC 4039), whose length is 0. Signed-off-by: Stefano Brivio --- dhcp.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/dhcp.c b/dhcp.c index a06f143..387aee3 100644 --- a/dhcp.c +++ b/dhcp.c @@ -36,9 +36,9 @@ /** * struct opt - DHCP option * @sent: Convenience flag, set while filling replies - * @slen: Length of option defined for server + * @slen: Length of option defined for server, -1 if not going to be sent * @s: Option payload from server - * @clen: Length of option received from client + * @clen: Length of option received from client, -1 if not received * @c: Option payload from client */ struct opt { @@ -68,6 +68,11 @@ static struct opt opts[255]; */ void dhcp_init(void) { + int i; + + for (i = 0; i < ARRAY_SIZE(opts); i++) + opts[i].slen = -1; + opts[1] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Mask */ opts[3] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Router */ opts[51] = (struct opt) { 0, 4, { 0xff, @@ -154,17 +159,17 @@ static int fill(struct msg *m) * option 53 at the beginning of the list. * Put it there explicitly, unless requested via option 55. */ - if (!memchr(opts[55].c, 53, opts[55].clen)) + if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen)) fill_one(m, 53, &offset); for (i = 0; i < opts[55].clen; i++) { o = opts[55].c[i]; - if (opts[o].slen) + if (opts[o].slen != -1) fill_one(m, o, &offset); } for (o = 0; o < 255; o++) { - if (opts[o].slen && !opts[o].sent) + if (opts[o].slen != -1 && !opts[o].sent) fill_one(m, o, &offset); } @@ -264,6 +269,9 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len) ".\xc0"); } } + + if (!opts[119].slen) + opts[119].slen = -1; } /** @@ -313,6 +321,9 @@ int dhcp(const struct ctx *c, const struct pool *p) offset += offsetof(struct msg, o); + for (i = 0; i < ARRAY_SIZE(opts); i++) + opts[i].clen = -1; + while (opt_off + 2 < opt_len) { const uint8_t *olen, *val; uint8_t *type; @@ -331,11 +342,12 @@ int dhcp(const struct ctx *c, const struct pool *p) opt_off += *olen + 2; } - if (opts[53].c[0] == DHCPDISCOVER) { + if (opts[53].clen > 0 && opts[53].c[0] == DHCPDISCOVER) { info("DHCP: offer to discover"); opts[53].s[0] = DHCPOFFER; - } else if (opts[53].c[0] == DHCPREQUEST || !opts[53].clen) { - info("%s: ack to request", opts[53].clen ? "DHCP" : "BOOTP"); + } else if (opts[53].clen <= 0 || opts[53].c[0] == DHCPREQUEST) { + info("%s: ack to request", /* DHCP needs a valid message type */ + (opts[53].clen <= 0) ? "BOOTP" : "DHCP"); opts[53].s[0] = DHCPACK; } else { return -1; @@ -374,6 +386,8 @@ int dhcp(const struct ctx *c, const struct pool *p) ((struct in_addr *)opts[6].s)[i] = c->ip4.dns[i]; opts[6].slen += sizeof(uint32_t); } + if (!opts[6].slen) + opts[6].slen = -1; if (!c->no_dhcp_dns_search) opt_set_dns_search(c, sizeof(m->o)); -- 2.43.0

Stefano Brivio

7:42 a.m.

New subject: [PATCH v4 1/3] dhcp: Use -1 as "missing option" length instead of 0

On Tue, 26 Nov 2024 07:34:08 +0100 Stefano Brivio wrote:

...

We want to add support for option 80 (Rapid Commit, RFC 4039), whose length is 0.

Signed-off-by: Stefano Brivio --- dhcp.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/dhcp.c b/dhcp.c index a06f143..387aee3 100644 --- a/dhcp.c +++ b/dhcp.c @@ -36,9 +36,9 @@ /** * struct opt - DHCP option * @sent: Convenience flag, set while filling replies - * @slen: Length of option defined for server + * @slen: Length of option defined for server, -1 if not going to be sent * @s: Option payload from server - * @clen: Length of option received from client + * @clen: Length of option received from client, -1 if not received * @c: Option payload from client */ struct opt { @@ -68,6 +68,11 @@ static struct opt opts[255]; */ void dhcp_init(void) { + int i; + + for (i = 0; i < ARRAY_SIZE(opts); i++) + opts[i].slen = -1; + opts[1] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Mask */ opts[3] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, }; /* Router */ opts[51] = (struct opt) { 0, 4, { 0xff, @@ -154,17 +159,17 @@ static int fill(struct msg *m) * option 53 at the beginning of the list. * Put it there explicitly, unless requested via option 55. */ - if (!memchr(opts[55].c, 53, opts[55].clen)) + if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen)) fill_one(m, 53, &offset);

for (i = 0; i < opts[55].clen; i++) { o = opts[55].c[i]; - if (opts[o].slen) + if (opts[o].slen != -1) fill_one(m, o, &offset); }

for (o = 0; o < 255; o++) { - if (opts[o].slen && !opts[o].sent) + if (opts[o].slen != -1 && !opts[o].sent) fill_one(m, o, &offset); }

@@ -264,6 +269,9 @@ static void opt_set_dns_search(const struct ctx *c, size_t max_len) ".\xc0"); } } + + if (!opts[119].slen) + opts[119].slen = -1; }

/** @@ -313,6 +321,9 @@ int dhcp(const struct ctx *c, const struct pool *p)

offset += offsetof(struct msg, o);

+ for (i = 0; i < ARRAY_SIZE(opts); i++) + opts[i].clen = -1; + while (opt_off + 2 < opt_len) { const uint8_t *olen, *val; uint8_t *type; @@ -331,11 +342,12 @@ int dhcp(const struct ctx *c, const struct pool *p) opt_off += *olen + 2; }

- if (opts[53].c[0] == DHCPDISCOVER) { + if (opts[53].clen > 0 && opts[53].c[0] == DHCPDISCOVER) { info("DHCP: offer to discover"); opts[53].s[0] = DHCPOFFER; - } else if (opts[53].c[0] == DHCPREQUEST || !opts[53].clen) { - info("%s: ack to request", opts[53].clen ? "DHCP" : "BOOTP"); + } else if (opts[53].clen <= 0 || opts[53].c[0] == DHCPREQUEST) { + info("%s: ack to request", /* DHCP needs a valid message type */ + (opts[53].clen <= 0) ? "BOOTP" : "DHCP");

Oops, posted before tests completed, this is broken again... -- Stefano

Stefano Brivio

7:34 a.m.

New subject: [PATCH v4 2/3] dhcp: Introduce support for Rapid Commit (option 80, RFC 4039)

I'm trying to speed up and simplify IP address acquisition in muvm. Signed-off-by: Stefano Brivio --- dhcp.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/dhcp.c b/dhcp.c index 387aee3..732eb06 100644 --- a/dhcp.c +++ b/dhcp.c @@ -342,10 +342,17 @@ int dhcp(const struct ctx *c, const struct pool *p) opt_off += *olen + 2; } + opts[80].slen = -1; if (opts[53].clen > 0 && opts[53].c[0] == DHCPDISCOVER) { - info("DHCP: offer to discover"); - opts[53].s[0] = DHCPOFFER; - } else if (opts[53].clen <= 0 || opts[53].c[0] == DHCPREQUEST) { + if (opts[80].clen == -1) { + info("DHCP: offer to discover"); + opts[53].s[0] = DHCPOFFER; + } else { + info("DHCP: ack to discover (Rapid Commit)"); + opts[53].s[0] = DHCPACK; + opts[80].slen = 0; + } + } else if (opts[53].clen <= 0 && opts[53].c[0] == DHCPREQUEST) { info("%s: ack to request", /* DHCP needs a valid message type */ (opts[53].clen <= 0) ? "BOOTP" : "DHCP"); opts[53].s[0] = DHCPACK; -- 2.43.0

Stefano Brivio

7:34 a.m.

New subject: [PATCH v4 3/3] 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 732eb06..665a325 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 */ -- 2.43.0

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Stefano Brivio