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=202510 header.b=h2yYDG91; dkim-atps=neutral Received: from mail.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by passt.top (Postfix) with ESMTPS id 61E005A095E for ; Wed, 19 Nov 2025 06:23:07 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202510; t=1763529779; bh=bdIolG5VF3nQWFgdxo64QvDzjFBymHv0hDMXNg0yxD4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=h2yYDG913LtXLwzHlXj+kuSDvEsyrVESunPLxXfsLdw1TiZ8oAEX+GT6lhVytpayZ ydx2YtWDWievtFaBP4wfnsOuECW7tdpPSCl/r2IOrC/gp9MbJQzSrNOM8UYoJP/12+ JA1BUynpjNnlIz2E9ehVMDLK7hxxfwO/DKHjVKRB1B/eomrvK/hyZz9RwS770iy4vV 3Rjw2KMh8lRUwzWpOeMjFWj6SCBBS9lt+rH0w+3tdIYptEWionnXt6Ob4Foo6xPq5t 2Yco+CrAVX0tMD1pkZkz/ESgFhgwhVSmCwipBLMA4HjwE2B9jEQ8qPV3un9DQR0bBT 0c2tWjuCdouJw== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4dB8yC4gpfz4wH6; Wed, 19 Nov 2025 16:22:59 +1100 (AEDT) From: David Gibson To: Stefano Brivio , passt-dev@passt.top Subject: [PATCH v4 9/9] tcp, udp: Bind outbound listening sockets by interface instead of address Date: Wed, 19 Nov 2025 16:22:57 +1100 Message-ID: <20251119052257.3004500-10-david@gibson.dropbear.id.au> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251119052257.3004500-1-david@gibson.dropbear.id.au> References: <20251119052257.3004500-1-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-ID-Hash: CSNZLC746VIMD4YHQTDMECWCI75NBAW4 X-Message-ID-Hash: CSNZLC746VIMD4YHQTDMECWCI75NBAW4 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, outbound forwards (-T, -U) are handled by sockets bound to the loopback address. Typically we create two sockets, one for 127.0.0.1 and one for ::1. This has some disadvantages: * The guest can't connect via 127.0.0.0/8 addresses other than 127.0.0.1 * We can't use dual-stack sockets, we have to have separate sockets for IPv4 and IPv6. The restriction exists for a reason though. If the guest has any interfaces other than pasta (e.g. a VPN tunnel) external hosts could reach the host via the forwards. Especially combined with -T auto / -U auto this would make it very easy to make a mistake with nasty security implications. We can achieve this a different way, however. Don't bind to a specific address, but _do_ use SO_BINDTODEVICE to restrict the sockets to the "lo" interface. Note that although traffic to a local but non-loopback address is passed over the 'lo' interface (as seen by netfilter and dumpcap), it doesn't count as attached to that interface for the purposes of SO_BINDTODEVICE (information from the routing table overrides the "physical" interface). So, this change doesn't help for bug 100. It's also not a complete fix for bug 113, it does however: * Get us a step closer to fixing bug 113 * Slightly simplify the code * Make things a bit easier to allow more flexible binding on the guest in in future Link: https://bugs.passt.top/show_bug.cgi?id=100 Link: https://bugs.passt.top/show_bug.cgi?id=113 Signed-off-by: David Gibson --- pif.c | 6 ------ tcp.c | 19 ++----------------- udp.c | 10 +++------- 3 files changed, 5 insertions(+), 30 deletions(-) diff --git a/pif.c b/pif.c index 85904f35..db447b4f 100644 --- a/pif.c +++ b/pif.c @@ -81,12 +81,6 @@ int pif_sock_l4(const struct ctx *c, enum epoll_type type, uint8_t pif, ASSERT(pif_is_socket(pif)); - if (pif == PIF_SPLICE) { - /* Sanity checks */ - ASSERT(!ifname); - ASSERT(addr && inany_is_loopback(addr)); - } - if (!addr) { ref.fd = sock_l4_dualstack(c, type, port, ifname); } else { diff --git a/tcp.c b/tcp.c index 2abb8be4..bd25952f 100644 --- a/tcp.c +++ b/tcp.c @@ -2618,21 +2618,6 @@ int tcp_sock_init(const struct ctx *c, uint8_t pif, return 0; } -/** - * tcp_ns_sock_init() - Init socket to listen for spliced outbound connections - * @c: Execution context - * @port: Port, host order - */ -static void tcp_ns_sock_init(const struct ctx *c, in_port_t port) -{ - ASSERT(!c->no_tcp); - - if (c->ifi4) - tcp_sock_init_one(c, PIF_SPLICE, &inany_loopback4, NULL, port); - if (c->ifi6) - tcp_sock_init_one(c, PIF_SPLICE, &inany_loopback6, NULL, port); -} - /** * tcp_ns_socks_init() - Bind sockets in namespace for outbound connections * @arg: Execution context @@ -2651,7 +2636,7 @@ static int tcp_ns_socks_init(void *arg) if (!bitmap_isset(c->tcp.fwd_out.map, port)) continue; - tcp_ns_sock_init(c, port); + tcp_sock_init(c, PIF_SPLICE, NULL, "lo", port); } return 0; @@ -2826,7 +2811,7 @@ static void tcp_port_rebind(struct ctx *c, bool outbound) if ((c->ifi4 && socks[port][V4] == -1) || (c->ifi6 && socks[port][V6] == -1)) { if (outbound) - tcp_ns_sock_init(c, port); + tcp_sock_init(c, PIF_SPLICE, NULL, "lo", port); else tcp_sock_init(c, PIF_HOST, NULL, NULL, port); } diff --git a/udp.c b/udp.c index 3d097fbb..f3d445cf 100644 --- a/udp.c +++ b/udp.c @@ -1213,14 +1213,10 @@ static void udp_port_rebind(struct ctx *c, bool outbound) if ((c->ifi4 && socks[V4][port] == -1) || (c->ifi6 && socks[V6][port] == -1)) { - if (outbound) { - udp_sock_init(c, PIF_SPLICE, - &inany_loopback4, NULL, port); - udp_sock_init(c, PIF_SPLICE, - &inany_loopback6, NULL, port); - } else { + if (outbound) + udp_sock_init(c, PIF_SPLICE, NULL, "lo", port); + else udp_sock_init(c, PIF_HOST, NULL, NULL, port); - } } } } -- 2.51.1