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![Fernando Fernandez Mancera](/assets/img/avatar_default.png)
Add ttl option support to the nftables "osf" expression. Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
432 lines
9.5 KiB
C
432 lines
9.5 KiB
C
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/capability.h>
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#include <linux/if.h>
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#include <linux/inetdevice.h>
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#include <linux/ip.h>
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#include <linux/list.h>
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#include <linux/rculist.h>
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#include <linux/skbuff.h>
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#include <linux/slab.h>
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#include <linux/tcp.h>
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#include <net/ip.h>
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#include <net/tcp.h>
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#include <linux/netfilter/nfnetlink.h>
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#include <linux/netfilter/x_tables.h>
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#include <net/netfilter/nf_log.h>
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#include <linux/netfilter/nfnetlink_osf.h>
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/*
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* Indexed by dont-fragment bit.
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* It is the only constant value in the fingerprint.
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*/
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struct list_head nf_osf_fingers[2];
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EXPORT_SYMBOL_GPL(nf_osf_fingers);
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static inline int nf_osf_ttl(const struct sk_buff *skb,
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int ttl_check, unsigned char f_ttl)
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{
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struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
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const struct iphdr *ip = ip_hdr(skb);
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int ret = 0;
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if (ttl_check == NF_OSF_TTL_TRUE)
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return ip->ttl == f_ttl;
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if (ttl_check == NF_OSF_TTL_NOCHECK)
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return 1;
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else if (ip->ttl <= f_ttl)
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return 1;
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for_ifa(in_dev) {
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if (inet_ifa_match(ip->saddr, ifa)) {
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ret = (ip->ttl == f_ttl);
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break;
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}
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}
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endfor_ifa(in_dev);
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return ret;
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}
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struct nf_osf_hdr_ctx {
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bool df;
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u16 window;
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u16 totlen;
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const unsigned char *optp;
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unsigned int optsize;
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};
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static bool nf_osf_match_one(const struct sk_buff *skb,
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const struct nf_osf_user_finger *f,
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int ttl_check,
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struct nf_osf_hdr_ctx *ctx)
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{
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unsigned int check_WSS = 0;
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int fmatch = FMATCH_WRONG;
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int foptsize, optnum;
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u16 mss = 0;
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if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
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return false;
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/*
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* Should not happen if userspace parser was written correctly.
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*/
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if (f->wss.wc >= OSF_WSS_MAX)
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return false;
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/* Check options */
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foptsize = 0;
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for (optnum = 0; optnum < f->opt_num; ++optnum)
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foptsize += f->opt[optnum].length;
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if (foptsize > MAX_IPOPTLEN ||
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ctx->optsize > MAX_IPOPTLEN ||
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ctx->optsize != foptsize)
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return false;
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check_WSS = f->wss.wc;
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for (optnum = 0; optnum < f->opt_num; ++optnum) {
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if (f->opt[optnum].kind == *ctx->optp) {
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__u32 len = f->opt[optnum].length;
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const __u8 *optend = ctx->optp + len;
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fmatch = FMATCH_OK;
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switch (*ctx->optp) {
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case OSFOPT_MSS:
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mss = ctx->optp[3];
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mss <<= 8;
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mss |= ctx->optp[2];
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mss = ntohs((__force __be16)mss);
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break;
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case OSFOPT_TS:
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break;
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}
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ctx->optp = optend;
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} else
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fmatch = FMATCH_OPT_WRONG;
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if (fmatch != FMATCH_OK)
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break;
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}
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if (fmatch != FMATCH_OPT_WRONG) {
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fmatch = FMATCH_WRONG;
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switch (check_WSS) {
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case OSF_WSS_PLAIN:
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if (f->wss.val == 0 || ctx->window == f->wss.val)
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fmatch = FMATCH_OK;
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break;
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case OSF_WSS_MSS:
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/*
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* Some smart modems decrease mangle MSS to
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* SMART_MSS_2, so we check standard, decreased
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* and the one provided in the fingerprint MSS
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* values.
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*/
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#define SMART_MSS_1 1460
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#define SMART_MSS_2 1448
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if (ctx->window == f->wss.val * mss ||
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ctx->window == f->wss.val * SMART_MSS_1 ||
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ctx->window == f->wss.val * SMART_MSS_2)
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fmatch = FMATCH_OK;
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break;
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case OSF_WSS_MTU:
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if (ctx->window == f->wss.val * (mss + 40) ||
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ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
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ctx->window == f->wss.val * (SMART_MSS_2 + 40))
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fmatch = FMATCH_OK;
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break;
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case OSF_WSS_MODULO:
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if ((ctx->window % f->wss.val) == 0)
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fmatch = FMATCH_OK;
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break;
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}
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}
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return fmatch == FMATCH_OK;
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}
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static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
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const struct sk_buff *skb,
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const struct iphdr *ip,
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unsigned char *opts)
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{
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const struct tcphdr *tcp;
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struct tcphdr _tcph;
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tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
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if (!tcp)
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return NULL;
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if (!tcp->syn)
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return NULL;
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ctx->totlen = ntohs(ip->tot_len);
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ctx->df = ntohs(ip->frag_off) & IP_DF;
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ctx->window = ntohs(tcp->window);
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if (tcp->doff * 4 > sizeof(struct tcphdr)) {
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ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
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ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
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sizeof(struct tcphdr), ctx->optsize, opts);
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}
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return tcp;
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}
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bool
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nf_osf_match(const struct sk_buff *skb, u_int8_t family,
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int hooknum, struct net_device *in, struct net_device *out,
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const struct nf_osf_info *info, struct net *net,
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const struct list_head *nf_osf_fingers)
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{
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const struct iphdr *ip = ip_hdr(skb);
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const struct nf_osf_user_finger *f;
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unsigned char opts[MAX_IPOPTLEN];
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const struct nf_osf_finger *kf;
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int fcount = 0, ttl_check;
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int fmatch = FMATCH_WRONG;
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struct nf_osf_hdr_ctx ctx;
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const struct tcphdr *tcp;
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memset(&ctx, 0, sizeof(ctx));
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tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
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if (!tcp)
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return false;
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ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;
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list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
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f = &kf->finger;
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if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
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continue;
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if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
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continue;
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fmatch = FMATCH_OK;
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fcount++;
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if (info->flags & NF_OSF_LOG)
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nf_log_packet(net, family, hooknum, skb,
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in, out, NULL,
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"%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
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f->genre, f->version, f->subtype,
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&ip->saddr, ntohs(tcp->source),
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&ip->daddr, ntohs(tcp->dest),
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f->ttl - ip->ttl);
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if ((info->flags & NF_OSF_LOG) &&
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info->loglevel == NF_OSF_LOGLEVEL_FIRST)
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break;
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}
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if (!fcount && (info->flags & NF_OSF_LOG))
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nf_log_packet(net, family, hooknum, skb, in, out, NULL,
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"Remote OS is not known: %pI4:%u -> %pI4:%u\n",
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&ip->saddr, ntohs(tcp->source),
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&ip->daddr, ntohs(tcp->dest));
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if (fcount)
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fmatch = FMATCH_OK;
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return fmatch == FMATCH_OK;
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}
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EXPORT_SYMBOL_GPL(nf_osf_match);
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const char *nf_osf_find(const struct sk_buff *skb,
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const struct list_head *nf_osf_fingers,
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const int ttl_check)
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{
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const struct iphdr *ip = ip_hdr(skb);
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const struct nf_osf_user_finger *f;
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unsigned char opts[MAX_IPOPTLEN];
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const struct nf_osf_finger *kf;
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struct nf_osf_hdr_ctx ctx;
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const struct tcphdr *tcp;
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const char *genre = NULL;
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memset(&ctx, 0, sizeof(ctx));
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tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
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if (!tcp)
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return NULL;
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list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
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f = &kf->finger;
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if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
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continue;
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genre = f->genre;
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break;
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}
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return genre;
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}
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EXPORT_SYMBOL_GPL(nf_osf_find);
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static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = {
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[OSF_ATTR_FINGER] = { .len = sizeof(struct nf_osf_user_finger) },
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};
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static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl,
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struct sk_buff *skb, const struct nlmsghdr *nlh,
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const struct nlattr * const osf_attrs[],
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struct netlink_ext_ack *extack)
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{
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struct nf_osf_user_finger *f;
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struct nf_osf_finger *kf = NULL, *sf;
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int err = 0;
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if (!capable(CAP_NET_ADMIN))
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return -EPERM;
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if (!osf_attrs[OSF_ATTR_FINGER])
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return -EINVAL;
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if (!(nlh->nlmsg_flags & NLM_F_CREATE))
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return -EINVAL;
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f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
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kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL);
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if (!kf)
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return -ENOMEM;
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memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger));
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list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
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if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
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continue;
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kfree(kf);
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kf = NULL;
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if (nlh->nlmsg_flags & NLM_F_EXCL)
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err = -EEXIST;
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break;
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}
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/*
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* We are protected by nfnl mutex.
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*/
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if (kf)
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list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]);
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return err;
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}
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static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl,
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struct sk_buff *skb,
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const struct nlmsghdr *nlh,
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const struct nlattr * const osf_attrs[],
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struct netlink_ext_ack *extack)
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{
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struct nf_osf_user_finger *f;
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struct nf_osf_finger *sf;
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int err = -ENOENT;
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if (!capable(CAP_NET_ADMIN))
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return -EPERM;
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if (!osf_attrs[OSF_ATTR_FINGER])
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return -EINVAL;
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f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
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list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
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if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger)))
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continue;
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/*
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* We are protected by nfnl mutex.
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*/
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list_del_rcu(&sf->finger_entry);
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kfree_rcu(sf, rcu_head);
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err = 0;
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break;
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}
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return err;
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}
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static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = {
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[OSF_MSG_ADD] = {
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.call = nfnl_osf_add_callback,
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.attr_count = OSF_ATTR_MAX,
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.policy = nfnl_osf_policy,
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},
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[OSF_MSG_REMOVE] = {
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.call = nfnl_osf_remove_callback,
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.attr_count = OSF_ATTR_MAX,
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.policy = nfnl_osf_policy,
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},
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};
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static const struct nfnetlink_subsystem nfnl_osf_subsys = {
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.name = "osf",
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.subsys_id = NFNL_SUBSYS_OSF,
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.cb_count = OSF_MSG_MAX,
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.cb = nfnl_osf_callbacks,
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};
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static int __init nfnl_osf_init(void)
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{
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int err = -EINVAL;
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int i;
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for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i)
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INIT_LIST_HEAD(&nf_osf_fingers[i]);
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err = nfnetlink_subsys_register(&nfnl_osf_subsys);
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if (err < 0) {
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pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
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goto err_out_exit;
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}
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return 0;
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err_out_exit:
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return err;
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}
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static void __exit nfnl_osf_fini(void)
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{
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struct nf_osf_finger *f;
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int i;
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nfnetlink_subsys_unregister(&nfnl_osf_subsys);
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rcu_read_lock();
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for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
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list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
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list_del_rcu(&f->finger_entry);
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kfree_rcu(f, rcu_head);
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}
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}
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rcu_read_unlock();
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rcu_barrier();
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}
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module_init(nfnl_osf_init);
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module_exit(nfnl_osf_fini);
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MODULE_LICENSE("GPL");
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