net/netfilter/nf_log_syslog.c

root/net/netfilter/nf_log_syslog.c
// SPDX-License-Identifier: GPL-2.0-only
/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/skbuff.h>
#include <linux/if_arp.h>
#include <linux/ip.h>
#include <net/ipv6.h>
#include <net/icmp.h>
#include <net/udp.h>
#include <net/tcp.h>
#include <net/route.h>

#include <linux/netfilter.h>
#include <linux/netfilter_bridge.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter/xt_LOG.h>
#include <net/netfilter/nf_log.h>

static const struct nf_loginfo default_loginfo = {
        .type   = NF_LOG_TYPE_LOG,
        .u = {
                .log = {
                        .level    = LOGLEVEL_NOTICE,
                        .logflags = NF_LOG_DEFAULT_MASK,
                },
        },
};

struct arppayload {
        unsigned char mac_src[ETH_ALEN];
        unsigned char ip_src[4];
        unsigned char mac_dst[ETH_ALEN];
        unsigned char ip_dst[4];
};

/* Guard against containers flooding syslog. */
static bool nf_log_allowed(const struct net *net)
{
        return net_eq(net, &init_net) || sysctl_nf_log_all_netns;
}

static void nf_log_dump_vlan(struct nf_log_buf *m, const struct sk_buff *skb)
{
        u16 vid;

        if (!skb_vlan_tag_present(skb))
                return;

        vid = skb_vlan_tag_get(skb);
        nf_log_buf_add(m, "VPROTO=%04x VID=%u ", ntohs(skb->vlan_proto), vid);
}
static void noinline_for_stack
dump_arp_packet(struct nf_log_buf *m,
                const struct nf_loginfo *info,
                const struct sk_buff *skb, unsigned int nhoff)
{
        const struct arppayload *ap;
        struct arppayload _arpp;
        const struct arphdr *ah;
        unsigned int logflags;
        struct arphdr _arph;

        ah = skb_header_pointer(skb, nhoff, sizeof(_arph), &_arph);
        if (!ah) {
                nf_log_buf_add(m, "TRUNCATED");
                return;
        }

        if (info->type == NF_LOG_TYPE_LOG)
                logflags = info->u.log.logflags;
        else
                logflags = NF_LOG_DEFAULT_MASK;

        if (logflags & NF_LOG_MACDECODE) {
                nf_log_buf_add(m, "MACSRC=%pM MACDST=%pM ",
                               eth_hdr(skb)->h_source, eth_hdr(skb)->h_dest);
                nf_log_dump_vlan(m, skb);
                nf_log_buf_add(m, "MACPROTO=%04x ",
                               ntohs(eth_hdr(skb)->h_proto));
        }

        nf_log_buf_add(m, "ARP HTYPE=%d PTYPE=0x%04x OPCODE=%d",
                       ntohs(ah->ar_hrd), ntohs(ah->ar_pro), ntohs(ah->ar_op));
        /* If it's for Ethernet and the lengths are OK, then log the ARP
         * payload.
         */
        if (ah->ar_hrd != htons(ARPHRD_ETHER) ||
            ah->ar_hln != ETH_ALEN ||
            ah->ar_pln != sizeof(__be32))
                return;

        ap = skb_header_pointer(skb, nhoff + sizeof(_arph), sizeof(_arpp), &_arpp);
        if (!ap) {
                nf_log_buf_add(m, " INCOMPLETE [%zu bytes]",
                               skb->len - sizeof(_arph));
                return;
        }
        nf_log_buf_add(m, " MACSRC=%pM IPSRC=%pI4 MACDST=%pM IPDST=%pI4",
                       ap->mac_src, ap->ip_src, ap->mac_dst, ap->ip_dst);
}

static void
nf_log_dump_packet_common(struct nf_log_buf *m, u8 pf,
                          unsigned int hooknum, const struct sk_buff *skb,
                          const struct net_device *in,
                          const struct net_device *out,
                          const struct nf_loginfo *loginfo, const char *prefix,
                          struct net *net)
{
        const struct net_device *physoutdev __maybe_unused;
        const struct net_device *physindev __maybe_unused;

        nf_log_buf_add(m, KERN_SOH "%c%sIN=%s OUT=%s ",
                       '0' + loginfo->u.log.level, prefix,
                        in ? in->name : "",
                        out ? out->name : "");
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        physindev = nf_bridge_get_physindev(skb, net);
        if (physindev && in != physindev)
                nf_log_buf_add(m, "PHYSIN=%s ", physindev->name);
        physoutdev = nf_bridge_get_physoutdev(skb);
        if (physoutdev && out != physoutdev)
                nf_log_buf_add(m, "PHYSOUT=%s ", physoutdev->name);
#endif
}

static void nf_log_arp_packet(struct net *net, u_int8_t pf,
                              unsigned int hooknum, const struct sk_buff *skb,
                              const struct net_device *in,
                              const struct net_device *out,
                              const struct nf_loginfo *loginfo,
                              const char *prefix)
{
        struct nf_log_buf *m;

        if (!nf_log_allowed(net))
                return;

        m = nf_log_buf_open();

        if (!loginfo)
                loginfo = &default_loginfo;

        nf_log_dump_packet_common(m, pf, hooknum, skb, in, out, loginfo,
                                  prefix, net);
        dump_arp_packet(m, loginfo, skb, skb_network_offset(skb));

        nf_log_buf_close(m);
}

static struct nf_logger nf_arp_logger __read_mostly = {
        .name           = "nf_log_arp",
        .type           = NF_LOG_TYPE_LOG,
        .logfn          = nf_log_arp_packet,
        .me             = THIS_MODULE,
};

static void nf_log_dump_sk_uid_gid(struct net *net, struct nf_log_buf *m,
                                   struct sock *sk)
{
        if (!sk || !sk_fullsock(sk) || !net_eq(net, sock_net(sk)))
                return;

        read_lock_bh(&sk->sk_callback_lock);
        if (sk->sk_socket && sk->sk_socket->file) {
                const struct cred *cred = sk->sk_socket->file->f_cred;

                nf_log_buf_add(m, "UID=%u GID=%u ",
                               from_kuid_munged(&init_user_ns, cred->fsuid),
                               from_kgid_munged(&init_user_ns, cred->fsgid));
        }
        read_unlock_bh(&sk->sk_callback_lock);
}

static noinline_for_stack int
nf_log_dump_tcp_header(struct nf_log_buf *m,
                       const struct sk_buff *skb,
                       u8 proto, int fragment,
                       unsigned int offset,
                       unsigned int logflags)
{
        struct tcphdr _tcph;
        const struct tcphdr *th;

        /* Max length: 10 "PROTO=TCP " */
        nf_log_buf_add(m, "PROTO=TCP ");

        if (fragment)
                return 0;

        /* Max length: 25 "INCOMPLETE [65535 bytes] " */
        th = skb_header_pointer(skb, offset, sizeof(_tcph), &_tcph);
        if (!th) {
                nf_log_buf_add(m, "INCOMPLETE [%u bytes] ", skb->len - offset);
                return 1;
        }

        /* Max length: 20 "SPT=65535 DPT=65535 " */
        nf_log_buf_add(m, "SPT=%u DPT=%u ",
                       ntohs(th->source), ntohs(th->dest));
        /* Max length: 30 "SEQ=4294967295 ACK=4294967295 " */
        if (logflags & NF_LOG_TCPSEQ) {
                nf_log_buf_add(m, "SEQ=%u ACK=%u ",
                               ntohl(th->seq), ntohl(th->ack_seq));
        }

        /* Max length: 13 "WINDOW=65535 " */
        nf_log_buf_add(m, "WINDOW=%u ", ntohs(th->window));
        /* Max length: 9 "RES=0x3C " */
        nf_log_buf_add(m, "RES=0x%02x ", (u_int8_t)(ntohl(tcp_flag_word(th) &
                                            TCP_RESERVED_BITS) >> 22));
        /* Max length: 35 "AE CWR ECE URG ACK PSH RST SYN FIN " */
        if (th->ae)
                nf_log_buf_add(m, "AE ");
        if (th->cwr)
                nf_log_buf_add(m, "CWR ");
        if (th->ece)
                nf_log_buf_add(m, "ECE ");
        if (th->urg)
                nf_log_buf_add(m, "URG ");
        if (th->ack)
                nf_log_buf_add(m, "ACK ");
        if (th->psh)
                nf_log_buf_add(m, "PSH ");
        if (th->rst)
                nf_log_buf_add(m, "RST ");
        if (th->syn)
                nf_log_buf_add(m, "SYN ");
        if (th->fin)
                nf_log_buf_add(m, "FIN ");
        /* Max length: 11 "URGP=65535 " */
        nf_log_buf_add(m, "URGP=%u ", ntohs(th->urg_ptr));

        if ((logflags & NF_LOG_TCPOPT) && th->doff * 4 > sizeof(struct tcphdr)) {
                unsigned int optsize = th->doff * 4 - sizeof(struct tcphdr);
                u8 _opt[60 - sizeof(struct tcphdr)];
                unsigned int i;
                const u8 *op;

                op = skb_header_pointer(skb, offset + sizeof(struct tcphdr),
                                        optsize, _opt);
                if (!op) {
                        nf_log_buf_add(m, "OPT (TRUNCATED)");
                        return 1;
                }

                /* Max length: 127 "OPT (" 15*4*2chars ") " */
                nf_log_buf_add(m, "OPT (");
                for (i = 0; i < optsize; i++)
                        nf_log_buf_add(m, "%02X", op[i]);

                nf_log_buf_add(m, ") ");
        }

        return 0;
}

static noinline_for_stack int
nf_log_dump_udp_header(struct nf_log_buf *m,
                       const struct sk_buff *skb,
                       u8 proto, int fragment,
                       unsigned int offset)
{
        struct udphdr _udph;
        const struct udphdr *uh;

        if (proto == IPPROTO_UDP)
                /* Max length: 10 "PROTO=UDP "     */
                nf_log_buf_add(m, "PROTO=UDP ");
        else    /* Max length: 14 "PROTO=UDPLITE " */
                nf_log_buf_add(m, "PROTO=UDPLITE ");

        if (fragment)
                goto out;

        /* Max length: 25 "INCOMPLETE [65535 bytes] " */
        uh = skb_header_pointer(skb, offset, sizeof(_udph), &_udph);
        if (!uh) {
                nf_log_buf_add(m, "INCOMPLETE [%u bytes] ", skb->len - offset);

                return 1;
        }

        /* Max length: 20 "SPT=65535 DPT=65535 " */
        nf_log_buf_add(m, "SPT=%u DPT=%u LEN=%u ",
                       ntohs(uh->source), ntohs(uh->dest), ntohs(uh->len));

out:
        return 0;
}

/* One level of recursion won't kill us */
static noinline_for_stack void
dump_ipv4_packet(struct net *net, struct nf_log_buf *m,
                 const struct nf_loginfo *info,
                 const struct sk_buff *skb, unsigned int iphoff)
{
        const struct iphdr *ih;
        unsigned int logflags;
        struct iphdr _iph;

        if (info->type == NF_LOG_TYPE_LOG)
                logflags = info->u.log.logflags;
        else
                logflags = NF_LOG_DEFAULT_MASK;

        ih = skb_header_pointer(skb, iphoff, sizeof(_iph), &_iph);
        if (!ih) {
                nf_log_buf_add(m, "TRUNCATED");
                return;
        }

        /* Important fields:
         * TOS, len, DF/MF, fragment offset, TTL, src, dst, options.
         * Max length: 40 "SRC=255.255.255.255 DST=255.255.255.255 "
         */
        nf_log_buf_add(m, "SRC=%pI4 DST=%pI4 ", &ih->saddr, &ih->daddr);

        /* Max length: 46 "LEN=65535 TOS=0xFF PREC=0xFF TTL=255 ID=65535 " */
        nf_log_buf_add(m, "LEN=%u TOS=0x%02X PREC=0x%02X TTL=%u ID=%u ",
                       iph_totlen(skb, ih), ih->tos & IPTOS_TOS_MASK,
                       ih->tos & IPTOS_PREC_MASK, ih->ttl, ntohs(ih->id));

        /* Max length: 6 "CE DF MF " */
        if (ntohs(ih->frag_off) & IP_CE)
                nf_log_buf_add(m, "CE ");
        if (ntohs(ih->frag_off) & IP_DF)
                nf_log_buf_add(m, "DF ");
        if (ntohs(ih->frag_off) & IP_MF)
                nf_log_buf_add(m, "MF ");

        /* Max length: 11 "FRAG:65535 " */
        if (ntohs(ih->frag_off) & IP_OFFSET)
                nf_log_buf_add(m, "FRAG:%u ", ntohs(ih->frag_off) & IP_OFFSET);

        if ((logflags & NF_LOG_IPOPT) &&
            ih->ihl * 4 > sizeof(struct iphdr)) {
                unsigned char _opt[4 * 15 - sizeof(struct iphdr)];
                const unsigned char *op;
                unsigned int i, optsize;

                optsize = ih->ihl * 4 - sizeof(struct iphdr);
                op = skb_header_pointer(skb, iphoff + sizeof(_iph),
                                        optsize, _opt);
                if (!op) {
                        nf_log_buf_add(m, "TRUNCATED");
                        return;
                }

                /* Max length: 127 "OPT (" 15*4*2chars ") " */
                nf_log_buf_add(m, "OPT (");
                for (i = 0; i < optsize; i++)
                        nf_log_buf_add(m, "%02X", op[i]);
                nf_log_buf_add(m, ") ");
        }

        switch (ih->protocol) {
        case IPPROTO_TCP:
                if (nf_log_dump_tcp_header(m, skb, ih->protocol,
                                           ntohs(ih->frag_off) & IP_OFFSET,
                                           iphoff + ih->ihl * 4, logflags))
                        return;
                break;
        case IPPROTO_UDP:
        case IPPROTO_UDPLITE:
                if (nf_log_dump_udp_header(m, skb, ih->protocol,
                                           ntohs(ih->frag_off) & IP_OFFSET,
                                           iphoff + ih->ihl * 4))
                        return;
                break;
        case IPPROTO_ICMP: {
                static const size_t required_len[NR_ICMP_TYPES + 1] = {
                        [ICMP_ECHOREPLY] = 4,
                        [ICMP_DEST_UNREACH] = 8 + sizeof(struct iphdr),
                        [ICMP_SOURCE_QUENCH] = 8 + sizeof(struct iphdr),
                        [ICMP_REDIRECT] = 8 + sizeof(struct iphdr),
                        [ICMP_ECHO] = 4,
                        [ICMP_TIME_EXCEEDED] = 8 + sizeof(struct iphdr),
                        [ICMP_PARAMETERPROB] = 8 + sizeof(struct iphdr),
                        [ICMP_TIMESTAMP] = 20,
                        [ICMP_TIMESTAMPREPLY] = 20,
                        [ICMP_ADDRESS] = 12,
                        [ICMP_ADDRESSREPLY] = 12 };
                const struct icmphdr *ich;
                struct icmphdr _icmph;

                /* Max length: 11 "PROTO=ICMP " */
                nf_log_buf_add(m, "PROTO=ICMP ");

                if (ntohs(ih->frag_off) & IP_OFFSET)
                        break;

                /* Max length: 25 "INCOMPLETE [65535 bytes] " */
                ich = skb_header_pointer(skb, iphoff + ih->ihl * 4,
                                         sizeof(_icmph), &_icmph);
                if (!ich) {
                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] ",
                                       skb->len - iphoff - ih->ihl * 4);
                        break;
                }

                /* Max length: 18 "TYPE=255 CODE=255 " */
                nf_log_buf_add(m, "TYPE=%u CODE=%u ", ich->type, ich->code);

                /* Max length: 25 "INCOMPLETE [65535 bytes] " */
                if (ich->type <= NR_ICMP_TYPES &&
                    required_len[ich->type] &&
                    skb->len - iphoff - ih->ihl * 4 < required_len[ich->type]) {
                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] ",
                                       skb->len - iphoff - ih->ihl * 4);
                        break;
                }

                switch (ich->type) {
                case ICMP_ECHOREPLY:
                case ICMP_ECHO:
                        /* Max length: 19 "ID=65535 SEQ=65535 " */
                        nf_log_buf_add(m, "ID=%u SEQ=%u ",
                                       ntohs(ich->un.echo.id),
                                       ntohs(ich->un.echo.sequence));
                        break;

                case ICMP_PARAMETERPROB:
                        /* Max length: 14 "PARAMETER=255 " */
                        nf_log_buf_add(m, "PARAMETER=%u ",
                                       ntohl(ich->un.gateway) >> 24);
                        break;
                case ICMP_REDIRECT:
                        /* Max length: 24 "GATEWAY=255.255.255.255 " */
                        nf_log_buf_add(m, "GATEWAY=%pI4 ", &ich->un.gateway);
                        fallthrough;
                case ICMP_DEST_UNREACH:
                case ICMP_SOURCE_QUENCH:
                case ICMP_TIME_EXCEEDED:
                        /* Max length: 3+maxlen */
                        if (!iphoff) { /* Only recurse once. */
                                nf_log_buf_add(m, "[");
                                dump_ipv4_packet(net, m, info, skb,
                                                 iphoff + ih->ihl * 4 + sizeof(_icmph));
                                nf_log_buf_add(m, "] ");
                        }

                        /* Max length: 10 "MTU=65535 " */
                        if (ich->type == ICMP_DEST_UNREACH &&
                            ich->code == ICMP_FRAG_NEEDED) {
                                nf_log_buf_add(m, "MTU=%u ",
                                               ntohs(ich->un.frag.mtu));
                        }
                }
                break;
        }
        /* Max Length */
        case IPPROTO_AH: {
                const struct ip_auth_hdr *ah;
                struct ip_auth_hdr _ahdr;

                if (ntohs(ih->frag_off) & IP_OFFSET)
                        break;

                /* Max length: 9 "PROTO=AH " */
                nf_log_buf_add(m, "PROTO=AH ");

                /* Max length: 25 "INCOMPLETE [65535 bytes] " */
                ah = skb_header_pointer(skb, iphoff + ih->ihl * 4,
                                        sizeof(_ahdr), &_ahdr);
                if (!ah) {
                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] ",
                                       skb->len - iphoff - ih->ihl * 4);
                        break;
                }

                /* Length: 15 "SPI=0xF1234567 " */
                nf_log_buf_add(m, "SPI=0x%x ", ntohl(ah->spi));
                break;
        }
        case IPPROTO_ESP: {
                const struct ip_esp_hdr *eh;
                struct ip_esp_hdr _esph;

                /* Max length: 10 "PROTO=ESP " */
                nf_log_buf_add(m, "PROTO=ESP ");

                if (ntohs(ih->frag_off) & IP_OFFSET)
                        break;

                /* Max length: 25 "INCOMPLETE [65535 bytes] " */
                eh = skb_header_pointer(skb, iphoff + ih->ihl * 4,
                                        sizeof(_esph), &_esph);
                if (!eh) {
                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] ",
                                       skb->len - iphoff - ih->ihl * 4);
                        break;
                }

                /* Length: 15 "SPI=0xF1234567 " */
                nf_log_buf_add(m, "SPI=0x%x ", ntohl(eh->spi));
                break;
        }
        /* Max length: 10 "PROTO 255 " */
        default:
                nf_log_buf_add(m, "PROTO=%u ", ih->protocol);
        }

        /* Max length: 15 "UID=4294967295 " */
        if ((logflags & NF_LOG_UID) && !iphoff)
                nf_log_dump_sk_uid_gid(net, m, skb->sk);

        /* Max length: 16 "MARK=0xFFFFFFFF " */
        if (!iphoff && skb->mark)
                nf_log_buf_add(m, "MARK=0x%x ", skb->mark);

        /* Proto    Max log string length */
        /* IP:      40+46+6+11+127 = 230 */
        /* TCP:     10+max(25,20+30+13+9+35+11+127) = 255 */
        /* UDP:     10+max(25,20) = 35 */
        /* UDPLITE: 14+max(25,20) = 39 */
        /* ICMP:    11+max(25, 18+25+max(19,14,24+3+n+10,3+n+10)) = 91+n */
        /* ESP:     10+max(25)+15 = 50 */
        /* AH:      9+max(25)+15 = 49 */
        /* unknown: 10 */

        /* (ICMP allows recursion one level deep) */
        /* maxlen =  IP + ICMP +  IP + max(TCP,UDP,ICMP,unknown) */
        /* maxlen = 230+   91  + 230 + 255 = 806 */
}

static noinline_for_stack void
dump_ipv6_packet(struct net *net, struct nf_log_buf *m,
                 const struct nf_loginfo *info,
                 const struct sk_buff *skb, unsigned int ip6hoff,
                 int recurse)
{
        const struct ipv6hdr *ih;
        unsigned int hdrlen = 0;
        unsigned int logflags;
        struct ipv6hdr _ip6h;
        unsigned int ptr;
        u8 currenthdr;
        int fragment;

        if (info->type == NF_LOG_TYPE_LOG)
                logflags = info->u.log.logflags;
        else
                logflags = NF_LOG_DEFAULT_MASK;

        ih = skb_header_pointer(skb, ip6hoff, sizeof(_ip6h), &_ip6h);
        if (!ih) {
                nf_log_buf_add(m, "TRUNCATED");
                return;
        }

        /* Max length: 88 "SRC=0000.0000.0000.0000.0000.0000.0000.0000 DST=0000.0000.0000.0000.0000.0000.0000.0000 " */
        nf_log_buf_add(m, "SRC=%pI6 DST=%pI6 ", &ih->saddr, &ih->daddr);

        /* Max length: 44 "LEN=65535 TC=255 HOPLIMIT=255 FLOWLBL=FFFFF " */
        nf_log_buf_add(m, "LEN=%zu TC=%u HOPLIMIT=%u FLOWLBL=%u ",
                       ipv6_payload_len(skb, ih) + sizeof(struct ipv6hdr),
                       (ntohl(*(__be32 *)ih) & 0x0ff00000) >> 20,
                       ih->hop_limit,
                       (ntohl(*(__be32 *)ih) & 0x000fffff));

        fragment = 0;
        ptr = ip6hoff + sizeof(struct ipv6hdr);
        currenthdr = ih->nexthdr;
        while (currenthdr != NEXTHDR_NONE && nf_ip6_ext_hdr(currenthdr)) {
                struct ipv6_opt_hdr _hdr;
                const struct ipv6_opt_hdr *hp;

                hp = skb_header_pointer(skb, ptr, sizeof(_hdr), &_hdr);
                if (!hp) {
                        nf_log_buf_add(m, "TRUNCATED");
                        return;
                }

                /* Max length: 48 "OPT (...) " */
                if (logflags & NF_LOG_IPOPT)
                        nf_log_buf_add(m, "OPT ( ");

                switch (currenthdr) {
                case IPPROTO_FRAGMENT: {
                        struct frag_hdr _fhdr;
                        const struct frag_hdr *fh;

                        nf_log_buf_add(m, "FRAG:");
                        fh = skb_header_pointer(skb, ptr, sizeof(_fhdr),
                                                &_fhdr);
                        if (!fh) {
                                nf_log_buf_add(m, "TRUNCATED ");
                                return;
                        }

                        /* Max length: 6 "65535 " */
                        nf_log_buf_add(m, "%u ", ntohs(fh->frag_off) & 0xFFF8);

                        /* Max length: 11 "INCOMPLETE " */
                        if (fh->frag_off & htons(0x0001))
                                nf_log_buf_add(m, "INCOMPLETE ");

                        nf_log_buf_add(m, "ID:%08x ",
                                       ntohl(fh->identification));

                        if (ntohs(fh->frag_off) & 0xFFF8)
                                fragment = 1;

                        hdrlen = 8;
                        break;
                }
                case IPPROTO_DSTOPTS:
                case IPPROTO_ROUTING:
                case IPPROTO_HOPOPTS:
                        if (fragment) {
                                if (logflags & NF_LOG_IPOPT)
                                        nf_log_buf_add(m, ")");
                                return;
                        }
                        hdrlen = ipv6_optlen(hp);
                        break;
                /* Max Length */
                case IPPROTO_AH:
                        if (logflags & NF_LOG_IPOPT) {
                                struct ip_auth_hdr _ahdr;
                                const struct ip_auth_hdr *ah;

                                /* Max length: 3 "AH " */
                                nf_log_buf_add(m, "AH ");

                                if (fragment) {
                                        nf_log_buf_add(m, ")");
                                        return;
                                }

                                ah = skb_header_pointer(skb, ptr, sizeof(_ahdr),
                                                        &_ahdr);
                                if (!ah) {
                                        /* Max length: 26 "INCOMPLETE [65535 bytes] )" */
                                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] )",
                                                       skb->len - ptr);
                                        return;
                                }

                                /* Length: 15 "SPI=0xF1234567 */
                                nf_log_buf_add(m, "SPI=0x%x ", ntohl(ah->spi));
                        }

                        hdrlen = ipv6_authlen(hp);
                        break;
                case IPPROTO_ESP:
                        if (logflags & NF_LOG_IPOPT) {
                                struct ip_esp_hdr _esph;
                                const struct ip_esp_hdr *eh;

                                /* Max length: 4 "ESP " */
                                nf_log_buf_add(m, "ESP ");

                                if (fragment) {
                                        nf_log_buf_add(m, ")");
                                        return;
                                }

                                /* Max length: 26 "INCOMPLETE [65535 bytes] )" */
                                eh = skb_header_pointer(skb, ptr, sizeof(_esph),
                                                        &_esph);
                                if (!eh) {
                                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] )",
                                                       skb->len - ptr);
                                        return;
                                }

                                /* Length: 16 "SPI=0xF1234567 )" */
                                nf_log_buf_add(m, "SPI=0x%x )",
                                               ntohl(eh->spi));
                        }
                        return;
                default:
                        /* Max length: 20 "Unknown Ext Hdr 255" */
                        nf_log_buf_add(m, "Unknown Ext Hdr %u", currenthdr);
                        return;
                }
                if (logflags & NF_LOG_IPOPT)
                        nf_log_buf_add(m, ") ");

                currenthdr = hp->nexthdr;
                ptr += hdrlen;
        }

        switch (currenthdr) {
        case IPPROTO_TCP:
                if (nf_log_dump_tcp_header(m, skb, currenthdr, fragment,
                                           ptr, logflags))
                        return;
                break;
        case IPPROTO_UDP:
        case IPPROTO_UDPLITE:
                if (nf_log_dump_udp_header(m, skb, currenthdr, fragment, ptr))
                        return;
                break;
        case IPPROTO_ICMPV6: {
                struct icmp6hdr _icmp6h;
                const struct icmp6hdr *ic;

                /* Max length: 13 "PROTO=ICMPv6 " */
                nf_log_buf_add(m, "PROTO=ICMPv6 ");

                if (fragment)
                        break;

                /* Max length: 25 "INCOMPLETE [65535 bytes] " */
                ic = skb_header_pointer(skb, ptr, sizeof(_icmp6h), &_icmp6h);
                if (!ic) {
                        nf_log_buf_add(m, "INCOMPLETE [%u bytes] ",
                                       skb->len - ptr);
                        return;
                }

                /* Max length: 18 "TYPE=255 CODE=255 " */
                nf_log_buf_add(m, "TYPE=%u CODE=%u ",
                               ic->icmp6_type, ic->icmp6_code);

                switch (ic->icmp6_type) {
                case ICMPV6_ECHO_REQUEST:
                case ICMPV6_ECHO_REPLY:
                        /* Max length: 19 "ID=65535 SEQ=65535 " */
                        nf_log_buf_add(m, "ID=%u SEQ=%u ",
                                       ntohs(ic->icmp6_identifier),
                                       ntohs(ic->icmp6_sequence));
                        break;
                case ICMPV6_MGM_QUERY:
                case ICMPV6_MGM_REPORT:
                case ICMPV6_MGM_REDUCTION:
                        break;

                case ICMPV6_PARAMPROB:
                        /* Max length: 17 "POINTER=ffffffff " */
                        nf_log_buf_add(m, "POINTER=%08x ",
                                       ntohl(ic->icmp6_pointer));
                        fallthrough;
                case ICMPV6_DEST_UNREACH:
                case ICMPV6_PKT_TOOBIG:
                case ICMPV6_TIME_EXCEED:
                        /* Max length: 3+maxlen */
                        if (recurse) {
                                nf_log_buf_add(m, "[");
                                dump_ipv6_packet(net, m, info, skb,
                                                 ptr + sizeof(_icmp6h), 0);
                                nf_log_buf_add(m, "] ");
                        }

                        /* Max length: 10 "MTU=65535 " */
                        if (ic->icmp6_type == ICMPV6_PKT_TOOBIG) {
                                nf_log_buf_add(m, "MTU=%u ",
                                               ntohl(ic->icmp6_mtu));
                        }
                }
                break;
        }
        /* Max length: 10 "PROTO=255 " */
        default:
                nf_log_buf_add(m, "PROTO=%u ", currenthdr);
        }

        /* Max length: 15 "UID=4294967295 " */
        if ((logflags & NF_LOG_UID) && recurse)
                nf_log_dump_sk_uid_gid(net, m, skb->sk);

        /* Max length: 16 "MARK=0xFFFFFFFF " */
        if (recurse && skb->mark)
                nf_log_buf_add(m, "MARK=0x%x ", skb->mark);
}

static void dump_mac_header(struct nf_log_buf *m,
                            const struct nf_loginfo *info,
                            const struct sk_buff *skb)
{
        struct net_device *dev = skb->dev;
        unsigned int logflags = 0;

        if (info->type == NF_LOG_TYPE_LOG)
                logflags = info->u.log.logflags;

        if (!(logflags & NF_LOG_MACDECODE))
                goto fallback;

        switch (dev->type) {
        case ARPHRD_ETHER:
                nf_log_buf_add(m, "MACSRC=%pM MACDST=%pM ",
                               eth_hdr(skb)->h_source, eth_hdr(skb)->h_dest);
                nf_log_dump_vlan(m, skb);
                nf_log_buf_add(m, "MACPROTO=%04x ",
                               ntohs(eth_hdr(skb)->h_proto));
                return;
        default:
                break;
        }

fallback:
        nf_log_buf_add(m, "MAC=");
        if (dev->hard_header_len &&
            skb->mac_header != skb->network_header) {
                const unsigned char *p = skb_mac_header(skb);
                unsigned int i;

                if (dev->type == ARPHRD_SIT) {
                        p -= ETH_HLEN;

                        if (p < skb->head)
                                p = NULL;
                }

                if (p) {
                        nf_log_buf_add(m, "%02x", *p++);
                        for (i = 1; i < dev->hard_header_len; i++)
                                nf_log_buf_add(m, ":%02x", *p++);
                }

                if (dev->type == ARPHRD_SIT) {
                        const struct iphdr *iph =
                                (struct iphdr *)skb_mac_header(skb);

                        nf_log_buf_add(m, " TUNNEL=%pI4->%pI4", &iph->saddr,
                                       &iph->daddr);
                }
        }
        nf_log_buf_add(m, " ");
}

static void nf_log_ip_packet(struct net *net, u_int8_t pf,
                             unsigned int hooknum, const struct sk_buff *skb,
                             const struct net_device *in,
                             const struct net_device *out,
                             const struct nf_loginfo *loginfo,
                             const char *prefix)
{
        struct nf_log_buf *m;

        if (!nf_log_allowed(net))
                return;

        m = nf_log_buf_open();

        if (!loginfo)
                loginfo = &default_loginfo;

        nf_log_dump_packet_common(m, pf, hooknum, skb, in,
                                  out, loginfo, prefix, net);

        if (in)
                dump_mac_header(m, loginfo, skb);

        dump_ipv4_packet(net, m, loginfo, skb, skb_network_offset(skb));

        nf_log_buf_close(m);
}

static struct nf_logger nf_ip_logger __read_mostly = {
        .name           = "nf_log_ipv4",
        .type           = NF_LOG_TYPE_LOG,
        .logfn          = nf_log_ip_packet,
        .me             = THIS_MODULE,
};

static void nf_log_ip6_packet(struct net *net, u_int8_t pf,
                              unsigned int hooknum, const struct sk_buff *skb,
                              const struct net_device *in,
                              const struct net_device *out,
                              const struct nf_loginfo *loginfo,
                              const char *prefix)
{
        struct nf_log_buf *m;

        if (!nf_log_allowed(net))
                return;

        m = nf_log_buf_open();

        if (!loginfo)
                loginfo = &default_loginfo;

        nf_log_dump_packet_common(m, pf, hooknum, skb, in, out,
                                  loginfo, prefix, net);

        if (in)
                dump_mac_header(m, loginfo, skb);

        dump_ipv6_packet(net, m, loginfo, skb, skb_network_offset(skb), 1);

        nf_log_buf_close(m);
}

static struct nf_logger nf_ip6_logger __read_mostly = {
        .name           = "nf_log_ipv6",
        .type           = NF_LOG_TYPE_LOG,
        .logfn          = nf_log_ip6_packet,
        .me             = THIS_MODULE,
};

static void nf_log_unknown_packet(struct net *net, u_int8_t pf,
                                  unsigned int hooknum,
                                  const struct sk_buff *skb,
                                  const struct net_device *in,
                                  const struct net_device *out,
                                  const struct nf_loginfo *loginfo,
                                  const char *prefix)
{
        struct nf_log_buf *m;

        if (!nf_log_allowed(net))
                return;

        m = nf_log_buf_open();

        if (!loginfo)
                loginfo = &default_loginfo;

        nf_log_dump_packet_common(m, pf, hooknum, skb, in, out, loginfo,
                                  prefix, net);

        dump_mac_header(m, loginfo, skb);

        nf_log_buf_close(m);
}

static void nf_log_netdev_packet(struct net *net, u_int8_t pf,
                                 unsigned int hooknum,
                                 const struct sk_buff *skb,
                                 const struct net_device *in,
                                 const struct net_device *out,
                                 const struct nf_loginfo *loginfo,
                                 const char *prefix)
{
        switch (skb->protocol) {
        case htons(ETH_P_IP):
                nf_log_ip_packet(net, pf, hooknum, skb, in, out, loginfo, prefix);
                break;
        case htons(ETH_P_IPV6):
                nf_log_ip6_packet(net, pf, hooknum, skb, in, out, loginfo, prefix);
                break;
        case htons(ETH_P_ARP):
        case htons(ETH_P_RARP):
                nf_log_arp_packet(net, pf, hooknum, skb, in, out, loginfo, prefix);
                break;
        default:
                nf_log_unknown_packet(net, pf, hooknum, skb,
                                      in, out, loginfo, prefix);
                break;
        }
}

static struct nf_logger nf_netdev_logger __read_mostly = {
        .name           = "nf_log_netdev",
        .type           = NF_LOG_TYPE_LOG,
        .logfn          = nf_log_netdev_packet,
        .me             = THIS_MODULE,
};

static struct nf_logger nf_bridge_logger __read_mostly = {
        .name           = "nf_log_bridge",
        .type           = NF_LOG_TYPE_LOG,
        .logfn          = nf_log_netdev_packet,
        .me             = THIS_MODULE,
};

static int __net_init nf_log_syslog_net_init(struct net *net)
{
        int ret = nf_log_set(net, NFPROTO_IPV4, &nf_ip_logger);

        if (ret)
                return ret;

        ret = nf_log_set(net, NFPROTO_ARP, &nf_arp_logger);
        if (ret)
                goto err1;

        ret = nf_log_set(net, NFPROTO_IPV6, &nf_ip6_logger);
        if (ret)
                goto err2;

        ret = nf_log_set(net, NFPROTO_NETDEV, &nf_netdev_logger);
        if (ret)
                goto err3;

        ret = nf_log_set(net, NFPROTO_BRIDGE, &nf_bridge_logger);
        if (ret)
                goto err4;
        return 0;
err4:
        nf_log_unset(net, &nf_netdev_logger);
err3:
        nf_log_unset(net, &nf_ip6_logger);
err2:
        nf_log_unset(net, &nf_arp_logger);
err1:
        nf_log_unset(net, &nf_ip_logger);
        return ret;
}

static void __net_exit nf_log_syslog_net_exit(struct net *net)
{
        nf_log_unset(net, &nf_ip_logger);
        nf_log_unset(net, &nf_arp_logger);
        nf_log_unset(net, &nf_ip6_logger);
        nf_log_unset(net, &nf_netdev_logger);
        nf_log_unset(net, &nf_bridge_logger);
}

static struct pernet_operations nf_log_syslog_net_ops = {
        .init = nf_log_syslog_net_init,
        .exit = nf_log_syslog_net_exit,
};

static int __init nf_log_syslog_init(void)
{
        int ret;

        ret = register_pernet_subsys(&nf_log_syslog_net_ops);
        if (ret < 0)
                return ret;

        ret = nf_log_register(NFPROTO_IPV4, &nf_ip_logger);
        if (ret < 0)
                goto err1;

        ret = nf_log_register(NFPROTO_ARP, &nf_arp_logger);
        if (ret < 0)
                goto err2;

        ret = nf_log_register(NFPROTO_IPV6, &nf_ip6_logger);
        if (ret < 0)
                goto err3;

        ret = nf_log_register(NFPROTO_NETDEV, &nf_netdev_logger);
        if (ret < 0)
                goto err4;

        ret = nf_log_register(NFPROTO_BRIDGE, &nf_bridge_logger);
        if (ret < 0)
                goto err5;

        return 0;
err5:
        nf_log_unregister(&nf_netdev_logger);
err4:
        nf_log_unregister(&nf_ip6_logger);
err3:
        nf_log_unregister(&nf_arp_logger);
err2:
        nf_log_unregister(&nf_ip_logger);
err1:
        pr_err("failed to register logger\n");
        unregister_pernet_subsys(&nf_log_syslog_net_ops);
        return ret;
}

static void __exit nf_log_syslog_exit(void)
{
        unregister_pernet_subsys(&nf_log_syslog_net_ops);
        nf_log_unregister(&nf_ip_logger);
        nf_log_unregister(&nf_arp_logger);
        nf_log_unregister(&nf_ip6_logger);
        nf_log_unregister(&nf_netdev_logger);
        nf_log_unregister(&nf_bridge_logger);
}

module_init(nf_log_syslog_init);
module_exit(nf_log_syslog_exit);

MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("Netfilter syslog packet logging");
MODULE_LICENSE("GPL");
MODULE_ALIAS("nf_log_arp");
MODULE_ALIAS("nf_log_bridge");
MODULE_ALIAS("nf_log_ipv4");
MODULE_ALIAS("nf_log_ipv6");
MODULE_ALIAS("nf_log_netdev");
MODULE_ALIAS_NF_LOGGER(AF_BRIDGE, 0);
MODULE_ALIAS_NF_LOGGER(AF_INET, 0);
MODULE_ALIAS_NF_LOGGER(3, 0);
MODULE_ALIAS_NF_LOGGER(5, 0); /* NFPROTO_NETDEV */
MODULE_ALIAS_NF_LOGGER(AF_INET6, 0);
Linux
