From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202502 header.b=hjKmjACt; dkim-atps=neutral Received: from mail.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by passt.top (Postfix) with ESMTPS id 42FD25A0276 for ; Thu, 20 Feb 2025 06:25:32 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202502; t=1740029115; bh=x50bw8KM4sEgZz/r11mSpJ+is6U50Bnnc/WEpWgb3Wo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hjKmjACt+zY18vFeSyXMLCjgoEymFSkSUP4V16R5MjyBpxcmmdF5yPCHC+qwAIVIF Pykg8p26VNX3nYyofV/XDMPByMAhCr8hp+d0Fzhbf1OLyY0sCF2RnLuCLIZesNao1S oGM+mcfUmr2E2e3aQW4pDiIYNuJOP2j25F6D6zogiiFHWeSWB+lw9MWnxWMNMjXBn5 79KcZbD5dFqr4wrP7bLC731unnEOBD9WA54qy6ggfvVIBu3l7Q7ASDko5/54dl2iDG tVKSesvWyhxB+7rGOLi3WfYFlx4G4TxRTh8HW8Fvik3VKiXWcbUsSuJhXmzWye4MFu iMmvWSqc5siRQ== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4Yz1tM39SSz4wy6; Thu, 20 Feb 2025 16:25:15 +1100 (AEDT) From: David Gibson To: passt-dev@passt.top, Stefano Brivio Subject: [PATCH v2 1/1] conf: Be more precise about minimum MTUs Date: Thu, 20 Feb 2025 16:25:13 +1100 Message-ID: <20250220052513.1781759-2-david@gibson.dropbear.id.au> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250220052513.1781759-1-david@gibson.dropbear.id.au> References: <20250220052513.1781759-1-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-ID-Hash: H5DCUNIWUFFO76IXSX5QTEXC2HD3357Z X-Message-ID-Hash: H5DCUNIWUFFO76IXSX5QTEXC2HD3357Z X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: David Gibson X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: 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 --- conf.c | 26 +++++++++++++++++++------- ip.h | 7 +++++++ util.h | 6 ------ 3 files changed, 26 insertions(+), 13 deletions(-) diff --git a/conf.c b/conf.c index c5ee07b0..785be4f8 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; @@ -1838,10 +1838,22 @@ void conf(struct ctx *c, int argc, char **argv) log_conf_parsed = true; /* Stop printing everything */ nl_sock_init(c, false); - if (!v6_only) - c->ifi4 = conf_ip4(ifi4, &c->ip4); - if (!v4_only) - c->ifi6 = conf_ip6(ifi6, &c->ip6); + if (!v6_only) { + if (c->mtu < IPV4_MIN_MTU) { + warn("MTU %"PRIu16" is too small for IPv4 (minimum %u)", + c->mtu, IPV4_MIN_MTU); + } else { + c->ifi4 = conf_ip4(ifi4, &c->ip4); + } + } + if (!v4_only) { + if (c->mtu < IPV6_MIN_MTU) { + warn("MTU %"PRIu16" is too small for IPv6 (minimum %u)", + c->mtu, IPV6_MIN_MTU); + } else { + c->ifi6 = conf_ip6(ifi6, &c->ip6); + } + } if ((*c->ip4.ifname_out && !c->ifi4) || (*c->ip6.ifname_out && !c->ifi6)) die("External interface not usable"); diff --git a/ip.h b/ip.h index 1544dbf4..75351e2e 100644 --- a/ip.h +++ b/ip.h @@ -104,4 +104,11 @@ 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 50e96d32..0f70f4d4 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)) -- 2.48.1