From 1924e25f0723c0a86c1e33812f8e1d8aa045a146 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 5 Mar 2025 17:20:03 +1100 Subject: conf: Be more precise about minimum MTUs Currently we reject the -m option if given a value less than ETH_MIN_MTU (68). That define is derived from the kernel, but its name is misleading: it doesn't really have anything to do with Ethernet per se, but is rather the minimum payload any L2 link must be able to handle in order to carry IPv4. For IPv6, it's not sufficient: that requires an MTU of at least 1280. Newer kernels have better named constants IPV4_MIN_MTU and IPv6_MIN_MTU. Copy and use those constants instead, along with some more specific error messages. Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- conf.c | 18 +++++++++++++++--- ip.h | 7 +++++++ util.h | 6 ------ 3 files changed, 22 insertions(+), 9 deletions(-) diff --git a/conf.c b/conf.c index c5ee07b..065e720 100644 --- a/conf.c +++ b/conf.c @@ -1663,9 +1663,9 @@ void conf(struct ctx *c, int argc, char **argv) if (errno || *e) die("Invalid MTU: %s", optarg); - if (mtu && (mtu < ETH_MIN_MTU || mtu > ETH_MAX_MTU)) { - die("MTU %lu out of range (%u..%u)", mtu, - ETH_MIN_MTU, ETH_MAX_MTU); + if (mtu > ETH_MAX_MTU) { + die("MTU %lu too large (max %u)", + mtu, ETH_MAX_MTU); } c->mtu = mtu; @@ -1842,9 +1842,21 @@ void conf(struct ctx *c, int argc, char **argv) c->ifi4 = conf_ip4(ifi4, &c->ip4); if (!v4_only) c->ifi6 = conf_ip6(ifi6, &c->ip6); + + if (c->ifi4 && c->mtu < IPV4_MIN_MTU) { + warn("MTU %"PRIu16" is too small for IPv4 (minimum %u)", + c->mtu, IPV4_MIN_MTU); + } + if (c->ifi6 && c->mtu < IPV6_MIN_MTU) { + warn("MTU %"PRIu16" is too small for IPv6 (minimum %u)", + c->mtu, IPV6_MIN_MTU); + } + if ((*c->ip4.ifname_out && !c->ifi4) || (*c->ip6.ifname_out && !c->ifi6)) die("External interface not usable"); + + if (!c->ifi4 && !c->ifi6) { info("No external interface as template, switch to local mode"); diff --git a/ip.h b/ip.h index c82431e..471c57e 100644 --- a/ip.h +++ b/ip.h @@ -129,4 +129,11 @@ 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 }; +#ifndef IPV4_MIN_MTU +#define IPV4_MIN_MTU 68 +#endif +#ifndef IPV6_MIN_MTU +#define IPV6_MIN_MTU 1280 +#endif + #endif /* IP_H */ diff --git a/util.h b/util.h index 50e96d3..0f70f4d 100644 --- a/util.h +++ b/util.h @@ -34,15 +34,9 @@ #ifndef ETH_MAX_MTU #define ETH_MAX_MTU USHRT_MAX #endif -#ifndef ETH_MIN_MTU -#define ETH_MIN_MTU 68 -#endif #ifndef IP_MAX_MTU #define IP_MAX_MTU USHRT_MAX #endif -#ifndef IPV6_MIN_MTU -#define IPV6_MIN_MTU 1280 -#endif #ifndef MIN #define MIN(x, y) (((x) < (y)) ? (x) : (y)) -- cgit v1.2.3