From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5FB03C433F5 for ; Mon, 20 Dec 2021 14:32:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233671AbhLTOcy (ORCPT ); Mon, 20 Dec 2021 09:32:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233670AbhLTOcy (ORCPT ); Mon, 20 Dec 2021 09:32:54 -0500 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:12e:520::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01A48C061574 for ; Mon, 20 Dec 2021 06:32:53 -0800 (PST) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1mzJid-0006Qi-IU; Mon, 20 Dec 2021 15:32:51 +0100 From: Florian Westphal To: Cc: Florian Westphal Subject: [PATCH nf-next] netfilter: exthdr: add support for tcp option removal Date: Mon, 20 Dec 2021 15:32:47 +0100 Message-Id: <20211220143247.554667-1-fw@strlen.de> X-Mailer: git-send-email 2.33.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org This allows to replace a tcp option with nop padding to selectively disable a particular tcp option. Optstrip mode is chosen when userspace passes the exthdr expression with neither a source nor a destination register attribute. This is identical to xtables TCPOPTSTRIP extension. Signed-off-by: Florian Westphal --- proposed userspace syntax is: nft add rule f in delete tcp option sack-perm net/netfilter/nft_exthdr.c | 88 +++++++++++++++++++++++++++++++++++++- 1 file changed, 87 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c index dbe1f2e7dd9e..37e427ca2b34 100644 --- a/net/netfilter/nft_exthdr.c +++ b/net/netfilter/nft_exthdr.c @@ -308,6 +308,55 @@ static void nft_exthdr_tcp_set_eval(const struct nft_expr *expr, regs->verdict.code = NFT_BREAK; } +static void nft_exthdr_tcp_strip_eval(const struct nft_expr *expr, + struct nft_regs *regs, + const struct nft_pktinfo *pkt) +{ + u8 buff[sizeof(struct tcphdr) + MAX_TCP_OPTION_SPACE]; + struct nft_exthdr *priv = nft_expr_priv(expr); + unsigned int i, tcphdr_len, optl; + struct tcphdr *tcph; + u8 *opt; + + tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff, &tcphdr_len); + if (!tcph) + goto err; + + if (skb_ensure_writable(pkt->skb, nft_thoff(pkt) + tcphdr_len)) + goto err; + + opt = (u8 *)nft_tcp_header_pointer(pkt, sizeof(buff), buff, &tcphdr_len); + if (!opt) + goto err; + for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) { + unsigned int j; + + optl = optlen(opt, i); + if (priv->type != opt[i]) + continue; + + if (i + optl > tcphdr_len) + goto err; + + for (j = 0; j < optl; ++j) { + u16 n = TCPOPT_NOP; + u16 o = opt[i+j]; + + if ((i + j) % 2 == 0) { + o <<= 8; + n <<= 8; + } + inet_proto_csum_replace2(&tcph->check, pkt->skb, htons(o), + htons(n), false); + } + memset(opt + i, TCPOPT_NOP, optl); + return; + } + return; +err: + regs->verdict.code = NFT_BREAK; +} + static void nft_exthdr_sctp_eval(const struct nft_expr *expr, struct nft_regs *regs, const struct nft_pktinfo *pkt) @@ -457,6 +506,28 @@ static int nft_exthdr_tcp_set_init(const struct nft_ctx *ctx, priv->len); } +static int nft_exthdr_tcp_strip_init(const struct nft_ctx *ctx, + const struct nft_expr *expr, + const struct nlattr * const tb[]) +{ + struct nft_exthdr *priv = nft_expr_priv(expr); + + if (tb[NFTA_EXTHDR_SREG] || + tb[NFTA_EXTHDR_DREG] || + tb[NFTA_EXTHDR_FLAGS] || + tb[NFTA_EXTHDR_OFFSET] || + tb[NFTA_EXTHDR_LEN]) + return -EINVAL; + + if (!tb[NFTA_EXTHDR_TYPE]) + return -EINVAL; + + priv->type = nla_get_u8(tb[NFTA_EXTHDR_TYPE]); + priv->op = NFT_EXTHDR_OP_TCPOPT; + + return 0; +} + static int nft_exthdr_ipv4_init(const struct nft_ctx *ctx, const struct nft_expr *expr, const struct nlattr * const tb[]) @@ -517,6 +588,13 @@ static int nft_exthdr_dump_set(struct sk_buff *skb, const struct nft_expr *expr) return nft_exthdr_dump_common(skb, priv); } +static int nft_exthdr_dump_strip(struct sk_buff *skb, const struct nft_expr *expr) +{ + const struct nft_exthdr *priv = nft_expr_priv(expr); + + return nft_exthdr_dump_common(skb, priv); +} + static const struct nft_expr_ops nft_exthdr_ipv6_ops = { .type = &nft_exthdr_type, .size = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)), @@ -549,6 +627,14 @@ static const struct nft_expr_ops nft_exthdr_tcp_set_ops = { .dump = nft_exthdr_dump_set, }; +static const struct nft_expr_ops nft_exthdr_tcp_strip_ops = { + .type = &nft_exthdr_type, + .size = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)), + .eval = nft_exthdr_tcp_strip_eval, + .init = nft_exthdr_tcp_strip_init, + .dump = nft_exthdr_dump_strip, +}; + static const struct nft_expr_ops nft_exthdr_sctp_ops = { .type = &nft_exthdr_type, .size = NFT_EXPR_SIZE(sizeof(struct nft_exthdr)), @@ -576,7 +662,7 @@ nft_exthdr_select_ops(const struct nft_ctx *ctx, return &nft_exthdr_tcp_set_ops; if (tb[NFTA_EXTHDR_DREG]) return &nft_exthdr_tcp_ops; - break; + return &nft_exthdr_tcp_strip_ops; case NFT_EXTHDR_OP_IPV6: if (tb[NFTA_EXTHDR_DREG]) return &nft_exthdr_ipv6_ops; -- 2.33.1