@@ -835,6 +835,18 @@ config NETFILTER_XT_RATEEST
estimated by the RATEEST target.
The target allows you to measure rates similar to TC estimators.
+config NETFILTER_XT_TCPMSS
+ tristate '"TCPMSS" target and match support'
+ depends on IPV6 || IPV6=n
+ default m if NETFILTER_ADVANCED=n
+ help
+ This option adds the "TCPMSS" target and "tcpmss" match.
+
+ Netfilter tcpmss matching allows you to examine the MSS value of
+ TCP SYN packets, which control the maximum packet size for that connection.
+ The target allows you to alter the MSS value of TCP SYN packets,
+ to control the maximum size for that connection.
+
# alphabetically ordered list of targets
comment "Xtables targets"
@@ -1170,6 +1182,7 @@ config NETFILTER_XT_TARGET_TCPMSS
tristate '"TCPMSS" target support'
depends on IPV6 || IPV6=n
default m if NETFILTER_ADVANCED=n
+ select NETFILTER_XT_TCPMSS
help
This option adds a `TCPMSS' target, which allows you to alter the
MSS value of TCP SYN packets, to control the maximum size for that
@@ -1191,6 +1204,10 @@ config NETFILTER_XT_TARGET_TCPMSS
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
-j TCPMSS --clamp-mss-to-pmtu
+ This is a backwards-compat option for the user's convenience
+ (e.g. when running oldconfig). It selects
+ CONFIG_NETFILTER_XT_TCPMSS (combined tcpmss/TCPMSS module).
+
To compile it as a module, choose M here. If unsure, say N.
config NETFILTER_XT_TARGET_TCPOPTSTRIP
@@ -1687,11 +1704,16 @@ config NETFILTER_XT_MATCH_STRING
config NETFILTER_XT_MATCH_TCPMSS
tristate '"tcpmss" match support'
depends on NETFILTER_ADVANCED
+ select NETFILTER_XT_TCPMSS
help
This option adds a `tcpmss' match, which allows you to examine the
MSS value of TCP SYN packets, which control the maximum packet size
for that connection.
+ This is a backwards-compat option for the user's convenience
+ (e.g. when running oldconfig). It selects
+ CONFIG_NETFILTER_XT_TCPMSS (combined tcpmss/TCPMSS module).
+
To compile it as a module, choose M here. If unsure, say N.
config NETFILTER_XT_MATCH_TIME
@@ -163,6 +163,7 @@ obj-$(CONFIG_NETFILTER_XT_NAT) += xt_nat.o
obj-$(CONFIG_NETFILTER_XT_DSCP) += xt_dscp.o
obj-$(CONFIG_NETFILTER_XT_HL) += xt_hl.o
obj-$(CONFIG_NETFILTER_XT_RATEEST) += xt_rateest.o
+obj-$(CONFIG_NETFILTER_XT_TCPMSS) += xt_tcpmss.o
# targets
obj-$(CONFIG_NETFILTER_XT_TARGET_AUDIT) += xt_AUDIT.o
@@ -180,7 +181,6 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_REDIRECT) += xt_REDIRECT.o
obj-$(CONFIG_NETFILTER_XT_TARGET_MASQUERADE) += xt_MASQUERADE.o
obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TPROXY) += xt_TPROXY.o
-obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TCPOPTSTRIP) += xt_TCPOPTSTRIP.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TEE) += xt_TEE.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o
@@ -225,7 +225,6 @@ obj-$(CONFIG_NETFILTER_XT_MATCH_SOCKET) += xt_socket.o
obj-$(CONFIG_NETFILTER_XT_MATCH_STATE) += xt_state.o
obj-$(CONFIG_NETFILTER_XT_MATCH_STATISTIC) += xt_statistic.o
obj-$(CONFIG_NETFILTER_XT_MATCH_STRING) += xt_string.o
-obj-$(CONFIG_NETFILTER_XT_MATCH_TCPMSS) += xt_tcpmss.o
obj-$(CONFIG_NETFILTER_XT_MATCH_TIME) += xt_time.o
obj-$(CONFIG_NETFILTER_XT_MATCH_U32) += xt_u32.o
deleted file mode 100644
@@ -1,347 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * This is a module which is used for setting the MSS option in TCP packets.
- *
- * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
- * Copyright (C) 2007 Patrick McHardy <kaber@trash.net>
- */
-#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-#include <linux/module.h>
-#include <linux/skbuff.h>
-#include <linux/ip.h>
-#include <linux/gfp.h>
-#include <linux/ipv6.h>
-#include <linux/tcp.h>
-#include <net/dst.h>
-#include <net/flow.h>
-#include <net/ipv6.h>
-#include <net/route.h>
-#include <net/tcp.h>
-
-#include <linux/netfilter_ipv4/ip_tables.h>
-#include <linux/netfilter_ipv6/ip6_tables.h>
-#include <linux/netfilter/x_tables.h>
-#include <linux/netfilter/xt_tcpudp.h>
-#include <linux/netfilter/xt_tcpmss.h>
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
-MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment");
-MODULE_ALIAS("ipt_TCPMSS");
-MODULE_ALIAS("ip6t_TCPMSS");
-
-static inline unsigned int
-optlen(const u8 *opt, unsigned int offset)
-{
- /* Beware zero-length options: make finite progress */
- if (opt[offset] <= TCPOPT_NOP || opt[offset + 1] == 0)
- return 1;
- else
- return opt[offset + 1];
-}
-
-static u_int32_t tcpmss_reverse_mtu(struct net *net,
- const struct sk_buff *skb,
- unsigned int family)
-{
- struct flowi fl;
- struct rtable *rt = NULL;
- u32 mtu = ~0U;
-
- if (family == PF_INET) {
- struct flowi4 *fl4 = &fl.u.ip4;
-
- memset(fl4, 0, sizeof(*fl4));
- fl4->daddr = ip_hdr(skb)->saddr;
- } else {
- struct flowi6 *fl6 = &fl.u.ip6;
-
- memset(fl6, 0, sizeof(*fl6));
- fl6->daddr = ipv6_hdr(skb)->saddr;
- }
-
- nf_route(net, (struct dst_entry **)&rt, &fl, false, family);
- if (rt) {
- mtu = dst_mtu(&rt->dst);
- dst_release(&rt->dst);
- }
- return mtu;
-}
-
-static int
-tcpmss_mangle_packet(struct sk_buff *skb,
- const struct xt_action_param *par,
- unsigned int family,
- unsigned int tcphoff,
- unsigned int minlen)
-{
- const struct xt_tcpmss_info *info = par->targinfo;
- struct tcphdr *tcph;
- int len, tcp_hdrlen;
- unsigned int i;
- __be16 oldval;
- u16 newmss;
- u8 *opt;
-
- /* This is a fragment, no TCP header is available */
- if (par->fragoff != 0)
- return 0;
-
- if (skb_ensure_writable(skb, skb->len))
- return -1;
-
- len = skb->len - tcphoff;
- if (len < (int)sizeof(struct tcphdr))
- return -1;
-
- tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
- tcp_hdrlen = tcph->doff * 4;
-
- if (len < tcp_hdrlen || tcp_hdrlen < sizeof(struct tcphdr))
- return -1;
-
- if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
- struct net *net = xt_net(par);
- unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
- unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
-
- if (min_mtu <= minlen) {
- net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
- min_mtu);
- return -1;
- }
- newmss = min_mtu - minlen;
- } else {
- newmss = info->mss;
- }
-
- opt = (u_int8_t *)tcph;
- for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
- if (opt[i] == TCPOPT_MSS && opt[i + 1] == TCPOLEN_MSS) {
- u16 oldmss;
-
- oldmss = (opt[i + 2] << 8) | opt[i + 3];
-
- /* Never increase MSS, even when setting it, as
- * doing so results in problems for hosts that rely
- * on MSS being set correctly.
- */
- if (oldmss <= newmss)
- return 0;
-
- opt[i + 2] = (newmss & 0xff00) >> 8;
- opt[i + 3] = newmss & 0x00ff;
-
- inet_proto_csum_replace2(&tcph->check, skb,
- htons(oldmss), htons(newmss),
- false);
- return 0;
- }
- }
-
- /* There is data after the header so the option can't be added
- * without moving it, and doing so may make the SYN packet
- * itself too large. Accept the packet unmodified instead.
- */
- if (len > tcp_hdrlen)
- return 0;
-
- /* tcph->doff has 4 bits, do not wrap it to 0 */
- if (tcp_hdrlen >= 15 * 4)
- return 0;
-
- /*
- * MSS Option not found ?! add it..
- */
- if (skb_tailroom(skb) < TCPOLEN_MSS) {
- if (pskb_expand_head(skb, 0,
- TCPOLEN_MSS - skb_tailroom(skb),
- GFP_ATOMIC))
- return -1;
- tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
- }
-
- skb_put(skb, TCPOLEN_MSS);
-
- /*
- * IPv4: RFC 1122 states "If an MSS option is not received at
- * connection setup, TCP MUST assume a default send MSS of 536".
- * IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
- * length IPv6 header of 60, ergo the default MSS value is 1220
- * Since no MSS was provided, we must use the default values
- */
- if (xt_family(par) == NFPROTO_IPV4)
- newmss = min(newmss, (u16)536);
- else
- newmss = min(newmss, (u16)1220);
-
- opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
- memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
-
- inet_proto_csum_replace2(&tcph->check, skb,
- htons(len), htons(len + TCPOLEN_MSS), true);
- opt[0] = TCPOPT_MSS;
- opt[1] = TCPOLEN_MSS;
- opt[2] = (newmss & 0xff00) >> 8;
- opt[3] = newmss & 0x00ff;
-
- inet_proto_csum_replace4(&tcph->check, skb, 0, *((__be32 *)opt), false);
-
- oldval = ((__be16 *)tcph)[6];
- tcph->doff += TCPOLEN_MSS / 4;
- inet_proto_csum_replace2(&tcph->check, skb,
- oldval, ((__be16 *)tcph)[6], false);
- return TCPOLEN_MSS;
-}
-
-static unsigned int
-tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
-{
- struct iphdr *iph = ip_hdr(skb);
- __be16 newlen;
- int ret;
-
- ret = tcpmss_mangle_packet(skb, par,
- PF_INET,
- iph->ihl * 4,
- sizeof(*iph) + sizeof(struct tcphdr));
- if (ret < 0)
- return NF_DROP;
- if (ret > 0) {
- iph = ip_hdr(skb);
- newlen = htons(ntohs(iph->tot_len) + ret);
- csum_replace2(&iph->check, iph->tot_len, newlen);
- iph->tot_len = newlen;
- }
- return XT_CONTINUE;
-}
-
-#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
-static unsigned int
-tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
-{
- struct ipv6hdr *ipv6h = ipv6_hdr(skb);
- u8 nexthdr;
- __be16 frag_off, oldlen, newlen;
- int tcphoff;
- int ret;
-
- nexthdr = ipv6h->nexthdr;
- tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
- if (tcphoff < 0)
- return NF_DROP;
- ret = tcpmss_mangle_packet(skb, par,
- PF_INET6,
- tcphoff,
- sizeof(*ipv6h) + sizeof(struct tcphdr));
- if (ret < 0)
- return NF_DROP;
- if (ret > 0) {
- ipv6h = ipv6_hdr(skb);
- oldlen = ipv6h->payload_len;
- newlen = htons(ntohs(oldlen) + ret);
- if (skb->ip_summed == CHECKSUM_COMPLETE)
- skb->csum = csum_add(csum_sub(skb->csum, (__force __wsum)oldlen),
- (__force __wsum)newlen);
- ipv6h->payload_len = newlen;
- }
- return XT_CONTINUE;
-}
-#endif
-
-/* Must specify -p tcp --syn */
-static inline bool find_syn_match(const struct xt_entry_match *m)
-{
- const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data;
-
- if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
- tcpinfo->flg_cmp & TCPHDR_SYN &&
- !(tcpinfo->invflags & XT_TCP_INV_FLAGS))
- return true;
-
- return false;
-}
-
-static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
-{
- const struct xt_tcpmss_info *info = par->targinfo;
- const struct ipt_entry *e = par->entryinfo;
- const struct xt_entry_match *ematch;
-
- if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
- (par->hook_mask & ~((1 << NF_INET_FORWARD) |
- (1 << NF_INET_LOCAL_OUT) |
- (1 << NF_INET_POST_ROUTING))) != 0) {
- pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
- return -EINVAL;
- }
- if (par->nft_compat)
- return 0;
-
- xt_ematch_foreach(ematch, e)
- if (find_syn_match(ematch))
- return 0;
- pr_info_ratelimited("Only works on TCP SYN packets\n");
- return -EINVAL;
-}
-
-#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
-static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
-{
- const struct xt_tcpmss_info *info = par->targinfo;
- const struct ip6t_entry *e = par->entryinfo;
- const struct xt_entry_match *ematch;
-
- if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
- (par->hook_mask & ~((1 << NF_INET_FORWARD) |
- (1 << NF_INET_LOCAL_OUT) |
- (1 << NF_INET_POST_ROUTING))) != 0) {
- pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
- return -EINVAL;
- }
- if (par->nft_compat)
- return 0;
-
- xt_ematch_foreach(ematch, e)
- if (find_syn_match(ematch))
- return 0;
- pr_info_ratelimited("Only works on TCP SYN packets\n");
- return -EINVAL;
-}
-#endif
-
-static struct xt_target tcpmss_tg_reg[] __read_mostly = {
- {
- .family = NFPROTO_IPV4,
- .name = "TCPMSS",
- .checkentry = tcpmss_tg4_check,
- .target = tcpmss_tg4,
- .targetsize = sizeof(struct xt_tcpmss_info),
- .proto = IPPROTO_TCP,
- .me = THIS_MODULE,
- },
-#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
- {
- .family = NFPROTO_IPV6,
- .name = "TCPMSS",
- .checkentry = tcpmss_tg6_check,
- .target = tcpmss_tg6,
- .targetsize = sizeof(struct xt_tcpmss_info),
- .proto = IPPROTO_TCP,
- .me = THIS_MODULE,
- },
-#endif
-};
-
-static int __init tcpmss_tg_init(void)
-{
- return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
-}
-
-static void __exit tcpmss_tg_exit(void)
-{
- xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
-}
-
-module_init(tcpmss_tg_init);
-module_exit(tcpmss_tg_exit);
@@ -1,25 +1,37 @@
// SPDX-License-Identifier: GPL-2.0-only
-/* Kernel module to match TCP MSS values. */
-
-/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
+/* Kernel module for matching/modifying TCP MSS values/packets.
+ *
+ * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
* Portions (C) 2005 by Harald Welte <laforge@netfilter.org>
+ * Copyright (C) 2007 Patrick McHardy <kaber@trash.net>
*/
-
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <linux/gfp.h>
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
+#include <net/dst.h>
+#include <net/flow.h>
+#include <net/ipv6.h>
+#include <net/route.h>
#include <net/tcp.h>
-#include <linux/netfilter/xt_tcpmss.h>
-#include <linux/netfilter/x_tables.h>
-
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_tcpudp.h>
+#include <linux/netfilter/xt_tcpmss.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
-MODULE_DESCRIPTION("Xtables: TCP MSS match");
+MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment and match");
MODULE_ALIAS("ipt_tcpmss");
MODULE_ALIAS("ip6t_tcpmss");
+MODULE_ALIAS("ipt_TCPMSS");
+MODULE_ALIAS("ip6t_TCPMSS");
+MODULE_ALIAS("xt_TCPMSS");
static bool
tcpmss_mt(const struct sk_buff *skb, struct xt_action_param *par)
@@ -93,15 +105,329 @@ static struct xt_match tcpmss_mt_reg[] __read_mostly = {
},
};
-static int __init tcpmss_mt_init(void)
+static inline unsigned int
+optlen(const u8 *opt, unsigned int offset)
+{
+ /* Beware zero-length options: make finite progress */
+ if (opt[offset] <= TCPOPT_NOP || opt[offset + 1] == 0)
+ return 1;
+ else
+ return opt[offset + 1];
+}
+
+static u_int32_t tcpmss_reverse_mtu(struct net *net,
+ const struct sk_buff *skb,
+ unsigned int family)
+{
+ struct flowi fl;
+ struct rtable *rt = NULL;
+ u32 mtu = ~0U;
+
+ if (family == PF_INET) {
+ struct flowi4 *fl4 = &fl.u.ip4;
+
+ memset(fl4, 0, sizeof(*fl4));
+ fl4->daddr = ip_hdr(skb)->saddr;
+ } else {
+ struct flowi6 *fl6 = &fl.u.ip6;
+
+ memset(fl6, 0, sizeof(*fl6));
+ fl6->daddr = ipv6_hdr(skb)->saddr;
+ }
+
+ nf_route(net, (struct dst_entry **)&rt, &fl, false, family);
+ if (rt) {
+ mtu = dst_mtu(&rt->dst);
+ dst_release(&rt->dst);
+ }
+ return mtu;
+}
+
+static int
+tcpmss_mangle_packet(struct sk_buff *skb,
+ const struct xt_action_param *par,
+ unsigned int family,
+ unsigned int tcphoff,
+ unsigned int minlen)
+{
+ const struct xt_tcpmss_info *info = par->targinfo;
+ struct tcphdr *tcph;
+ int len, tcp_hdrlen;
+ unsigned int i;
+ __be16 oldval;
+ u16 newmss;
+ u8 *opt;
+
+ /* This is a fragment, no TCP header is available */
+ if (par->fragoff != 0)
+ return 0;
+
+ if (skb_ensure_writable(skb, skb->len))
+ return -1;
+
+ len = skb->len - tcphoff;
+ if (len < (int)sizeof(struct tcphdr))
+ return -1;
+
+ tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
+ tcp_hdrlen = tcph->doff * 4;
+
+ if (len < tcp_hdrlen || tcp_hdrlen < sizeof(struct tcphdr))
+ return -1;
+
+ if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
+ struct net *net = xt_net(par);
+ unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
+ unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
+
+ if (min_mtu <= minlen) {
+ net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
+ min_mtu);
+ return -1;
+ }
+ newmss = min_mtu - minlen;
+ } else {
+ newmss = info->mss;
+ }
+
+ opt = (u_int8_t *)tcph;
+ for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
+ if (opt[i] == TCPOPT_MSS && opt[i + 1] == TCPOLEN_MSS) {
+ u16 oldmss;
+
+ oldmss = (opt[i + 2] << 8) | opt[i + 3];
+
+ /* Never increase MSS, even when setting it, as
+ * doing so results in problems for hosts that rely
+ * on MSS being set correctly.
+ */
+ if (oldmss <= newmss)
+ return 0;
+
+ opt[i + 2] = (newmss & 0xff00) >> 8;
+ opt[i + 3] = newmss & 0x00ff;
+
+ inet_proto_csum_replace2(&tcph->check, skb,
+ htons(oldmss), htons(newmss),
+ false);
+ return 0;
+ }
+ }
+
+ /* There is data after the header so the option can't be added
+ * without moving it, and doing so may make the SYN packet
+ * itself too large. Accept the packet unmodified instead.
+ */
+ if (len > tcp_hdrlen)
+ return 0;
+
+ /* tcph->doff has 4 bits, do not wrap it to 0 */
+ if (tcp_hdrlen >= 15 * 4)
+ return 0;
+
+ /*
+ * MSS Option not found ?! add it..
+ */
+ if (skb_tailroom(skb) < TCPOLEN_MSS) {
+ if (pskb_expand_head(skb, 0,
+ TCPOLEN_MSS - skb_tailroom(skb),
+ GFP_ATOMIC))
+ return -1;
+ tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
+ }
+
+ skb_put(skb, TCPOLEN_MSS);
+
+ /*
+ * IPv4: RFC 1122 states "If an MSS option is not received at
+ * connection setup, TCP MUST assume a default send MSS of 536".
+ * IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
+ * length IPv6 header of 60, ergo the default MSS value is 1220
+ * Since no MSS was provided, we must use the default values
+ */
+ if (xt_family(par) == NFPROTO_IPV4)
+ newmss = min(newmss, (u16)536);
+ else
+ newmss = min(newmss, (u16)1220);
+
+ opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
+ memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
+
+ inet_proto_csum_replace2(&tcph->check, skb,
+ htons(len), htons(len + TCPOLEN_MSS), true);
+ opt[0] = TCPOPT_MSS;
+ opt[1] = TCPOLEN_MSS;
+ opt[2] = (newmss & 0xff00) >> 8;
+ opt[3] = newmss & 0x00ff;
+
+ inet_proto_csum_replace4(&tcph->check, skb, 0, *((__be32 *)opt), false);
+
+ oldval = ((__be16 *)tcph)[6];
+ tcph->doff += TCPOLEN_MSS / 4;
+ inet_proto_csum_replace2(&tcph->check, skb,
+ oldval, ((__be16 *)tcph)[6], false);
+ return TCPOLEN_MSS;
+}
+
+static unsigned int
+tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
+{
+ struct iphdr *iph = ip_hdr(skb);
+ __be16 newlen;
+ int ret;
+
+ ret = tcpmss_mangle_packet(skb, par,
+ PF_INET,
+ iph->ihl * 4,
+ sizeof(*iph) + sizeof(struct tcphdr));
+ if (ret < 0)
+ return NF_DROP;
+ if (ret > 0) {
+ iph = ip_hdr(skb);
+ newlen = htons(ntohs(iph->tot_len) + ret);
+ csum_replace2(&iph->check, iph->tot_len, newlen);
+ iph->tot_len = newlen;
+ }
+ return XT_CONTINUE;
+}
+
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+static unsigned int
+tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
+{
+ struct ipv6hdr *ipv6h = ipv6_hdr(skb);
+ u8 nexthdr;
+ __be16 frag_off, oldlen, newlen;
+ int tcphoff;
+ int ret;
+
+ nexthdr = ipv6h->nexthdr;
+ tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
+ if (tcphoff < 0)
+ return NF_DROP;
+ ret = tcpmss_mangle_packet(skb, par,
+ PF_INET6,
+ tcphoff,
+ sizeof(*ipv6h) + sizeof(struct tcphdr));
+ if (ret < 0)
+ return NF_DROP;
+ if (ret > 0) {
+ ipv6h = ipv6_hdr(skb);
+ oldlen = ipv6h->payload_len;
+ newlen = htons(ntohs(oldlen) + ret);
+ if (skb->ip_summed == CHECKSUM_COMPLETE)
+ skb->csum = csum_add(csum_sub(skb->csum, (__force __wsum)oldlen),
+ (__force __wsum)newlen);
+ ipv6h->payload_len = newlen;
+ }
+ return XT_CONTINUE;
+}
+#endif
+
+/* Must specify -p tcp --syn */
+static inline bool find_syn_match(const struct xt_entry_match *m)
+{
+ const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data;
+
+ if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
+ tcpinfo->flg_cmp & TCPHDR_SYN &&
+ !(tcpinfo->invflags & XT_TCP_INV_FLAGS))
+ return true;
+
+ return false;
+}
+
+static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
+{
+ const struct xt_tcpmss_info *info = par->targinfo;
+ const struct ipt_entry *e = par->entryinfo;
+ const struct xt_entry_match *ematch;
+
+ if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
+ (par->hook_mask & ~((1 << NF_INET_FORWARD) |
+ (1 << NF_INET_LOCAL_OUT) |
+ (1 << NF_INET_POST_ROUTING))) != 0) {
+ pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
+ return -EINVAL;
+ }
+ if (par->nft_compat)
+ return 0;
+
+ xt_ematch_foreach(ematch, e)
+ if (find_syn_match(ematch))
+ return 0;
+ pr_info_ratelimited("Only works on TCP SYN packets\n");
+ return -EINVAL;
+}
+
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
+{
+ const struct xt_tcpmss_info *info = par->targinfo;
+ const struct ip6t_entry *e = par->entryinfo;
+ const struct xt_entry_match *ematch;
+
+ if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
+ (par->hook_mask & ~((1 << NF_INET_FORWARD) |
+ (1 << NF_INET_LOCAL_OUT) |
+ (1 << NF_INET_POST_ROUTING))) != 0) {
+ pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
+ return -EINVAL;
+ }
+ if (par->nft_compat)
+ return 0;
+
+ xt_ematch_foreach(ematch, e)
+ if (find_syn_match(ematch))
+ return 0;
+ pr_info_ratelimited("Only works on TCP SYN packets\n");
+ return -EINVAL;
+}
+#endif
+
+static struct xt_target tcpmss_tg_reg[] __read_mostly = {
+ {
+ .family = NFPROTO_IPV4,
+ .name = "TCPMSS",
+ .checkentry = tcpmss_tg4_check,
+ .target = tcpmss_tg4,
+ .targetsize = sizeof(struct xt_tcpmss_info),
+ .proto = IPPROTO_TCP,
+ .me = THIS_MODULE,
+ },
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+ {
+ .family = NFPROTO_IPV6,
+ .name = "TCPMSS",
+ .checkentry = tcpmss_tg6_check,
+ .target = tcpmss_tg6,
+ .targetsize = sizeof(struct xt_tcpmss_info),
+ .proto = IPPROTO_TCP,
+ .me = THIS_MODULE,
+ },
+#endif
+};
+
+static int __init tcpmss_init(void)
{
- return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
+ int ret;
+
+ ret = xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
+ if (ret < 0)
+ return ret;
+ ret = xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
+ if (ret < 0) {
+ xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
+ return ret;
+ }
+ return 0;
}
-static void __exit tcpmss_mt_exit(void)
+static void __exit tcpmss_exit(void)
{
xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
+ xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
}
-module_init(tcpmss_mt_init);
-module_exit(tcpmss_mt_exit);
+module_init(tcpmss_init);
+module_exit(tcpmss_exit);