/* $OpenBSD: pf_norm.c,v 1.118 2009/06/25 09:30:28 sthen Exp $ */ /* * Copyright 2001 Niels Provos * Copyright 2009 Henning Brauer * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include "pflog.h" #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef INET6 #include #endif /* INET6 */ #include struct pf_frent { LIST_ENTRY(pf_frent) fr_next; struct ip *fr_ip; struct mbuf *fr_m; }; struct pf_frcache { LIST_ENTRY(pf_frcache) fr_next; uint16_t fr_off; uint16_t fr_end; }; #define PFFRAG_SEENLAST 0x0001 /* Seen the last fragment for this */ #define PFFRAG_NOBUFFER 0x0002 /* Non-buffering fragment cache */ #define PFFRAG_DROP 0x0004 /* Drop all fragments */ #define BUFFER_FRAGMENTS(fr) (!((fr)->fr_flags & PFFRAG_NOBUFFER)) struct pf_fragment { RB_ENTRY(pf_fragment) fr_entry; TAILQ_ENTRY(pf_fragment) frag_next; struct in_addr fr_src; struct in_addr fr_dst; u_int8_t fr_p; /* protocol of this fragment */ u_int8_t fr_flags; /* status flags */ u_int16_t fr_id; /* fragment id for reassemble */ u_int16_t fr_max; /* fragment data max */ u_int32_t fr_timeout; #define fr_queue fr_u.fru_queue #define fr_cache fr_u.fru_cache union { LIST_HEAD(pf_fragq, pf_frent) fru_queue; /* buffering */ LIST_HEAD(pf_cacheq, pf_frcache) fru_cache; /* non-buf */ } fr_u; }; TAILQ_HEAD(pf_fragqueue, pf_fragment) pf_fragqueue; TAILQ_HEAD(pf_cachequeue, pf_fragment) pf_cachequeue; static __inline int pf_frag_compare(struct pf_fragment *, struct pf_fragment *); RB_HEAD(pf_frag_tree, pf_fragment) pf_frag_tree, pf_cache_tree; RB_PROTOTYPE(pf_frag_tree, pf_fragment, fr_entry, pf_frag_compare); RB_GENERATE(pf_frag_tree, pf_fragment, fr_entry, pf_frag_compare); /* Private prototypes */ void pf_ip2key(struct pf_fragment *, struct ip *); void pf_remove_fragment(struct pf_fragment *); void pf_flush_fragments(void); void pf_free_fragment(struct pf_fragment *); struct pf_fragment *pf_find_fragment(struct ip *, struct pf_frag_tree *); struct mbuf *pf_reassemble(struct mbuf **, struct pf_fragment **, struct pf_frent *, int); void pf_scrub_ip(struct mbuf **, u_int16_t, u_int8_t, u_int8_t); #ifdef INET6 void pf_scrub_ip6(struct mbuf **, u_int8_t); #endif #define DPFPRINTF(x) do { \ if (pf_status.debug >= PF_DEBUG_MISC) { \ printf("%s: ", __func__); \ printf x ; \ } \ } while(0) /* Globals */ struct pool pf_frent_pl, pf_frag_pl, pf_cache_pl, pf_cent_pl; struct pool pf_state_scrub_pl; int pf_nfrents, pf_ncache; void pf_normalize_init(void) { pool_init(&pf_frent_pl, sizeof(struct pf_frent), 0, 0, 0, "pffrent", NULL); pool_init(&pf_frag_pl, sizeof(struct pf_fragment), 0, 0, 0, "pffrag", NULL); pool_init(&pf_cache_pl, sizeof(struct pf_fragment), 0, 0, 0, "pffrcache", NULL); pool_init(&pf_cent_pl, sizeof(struct pf_frcache), 0, 0, 0, "pffrcent", NULL); pool_init(&pf_state_scrub_pl, sizeof(struct pf_state_scrub), 0, 0, 0, "pfstscr", NULL); pool_sethiwat(&pf_frag_pl, PFFRAG_FRAG_HIWAT); pool_sethardlimit(&pf_frent_pl, PFFRAG_FRENT_HIWAT, NULL, 0); pool_sethardlimit(&pf_cache_pl, PFFRAG_FRCACHE_HIWAT, NULL, 0); pool_sethardlimit(&pf_cent_pl, PFFRAG_FRCENT_HIWAT, NULL, 0); TAILQ_INIT(&pf_fragqueue); TAILQ_INIT(&pf_cachequeue); } static __inline int pf_frag_compare(struct pf_fragment *a, struct pf_fragment *b) { int diff; if ((diff = a->fr_id - b->fr_id)) return (diff); else if ((diff = a->fr_p - b->fr_p)) return (diff); else if (a->fr_src.s_addr < b->fr_src.s_addr) return (-1); else if (a->fr_src.s_addr > b->fr_src.s_addr) return (1); else if (a->fr_dst.s_addr < b->fr_dst.s_addr) return (-1); else if (a->fr_dst.s_addr > b->fr_dst.s_addr) return (1); return (0); } void pf_purge_expired_fragments(void) { struct pf_fragment *frag; u_int32_t expire = time_second - pf_default_rule.timeout[PFTM_FRAG]; while ((frag = TAILQ_LAST(&pf_fragqueue, pf_fragqueue)) != NULL) { KASSERT(BUFFER_FRAGMENTS(frag)); if (frag->fr_timeout > expire) break; DPFPRINTF(("expiring %d(%p)\n", frag->fr_id, frag)); pf_free_fragment(frag); } while ((frag = TAILQ_LAST(&pf_cachequeue, pf_cachequeue)) != NULL) { KASSERT(!BUFFER_FRAGMENTS(frag)); if (frag->fr_timeout > expire) break; DPFPRINTF(("expiring %d(%p)\n", frag->fr_id, frag)); pf_free_fragment(frag); KASSERT(TAILQ_EMPTY(&pf_cachequeue) || TAILQ_LAST(&pf_cachequeue, pf_cachequeue) != frag); } } /* * Try to flush old fragments to make space for new ones */ void pf_flush_fragments(void) { struct pf_fragment *frag; int goal; goal = pf_nfrents * 9 / 10; DPFPRINTF(("trying to free > %d frents\n", pf_nfrents - goal)); while (goal < pf_nfrents) { frag = TAILQ_LAST(&pf_fragqueue, pf_fragqueue); if (frag == NULL) break; pf_free_fragment(frag); } goal = pf_ncache * 9 / 10; DPFPRINTF(("trying to free > %d cache entries\n", pf_ncache - goal)); while (goal < pf_ncache) { frag = TAILQ_LAST(&pf_cachequeue, pf_cachequeue); if (frag == NULL) break; pf_free_fragment(frag); } } /* Frees the fragments and all associated entries */ void pf_free_fragment(struct pf_fragment *frag) { struct pf_frent *frent; struct pf_frcache *frcache; /* Free all fragments */ if (BUFFER_FRAGMENTS(frag)) { for (frent = LIST_FIRST(&frag->fr_queue); frent; frent = LIST_FIRST(&frag->fr_queue)) { LIST_REMOVE(frent, fr_next); m_freem(frent->fr_m); pool_put(&pf_frent_pl, frent); pf_nfrents--; } } else { for (frcache = LIST_FIRST(&frag->fr_cache); frcache; frcache = LIST_FIRST(&frag->fr_cache)) { LIST_REMOVE(frcache, fr_next); KASSERT(LIST_EMPTY(&frag->fr_cache) || LIST_FIRST(&frag->fr_cache)->fr_off > frcache->fr_end); pool_put(&pf_cent_pl, frcache); pf_ncache--; } } pf_remove_fragment(frag); } void pf_ip2key(struct pf_fragment *key, struct ip *ip) { key->fr_p = ip->ip_p; key->fr_id = ip->ip_id; key->fr_src.s_addr = ip->ip_src.s_addr; key->fr_dst.s_addr = ip->ip_dst.s_addr; } struct pf_fragment * pf_find_fragment(struct ip *ip, struct pf_frag_tree *tree) { struct pf_fragment key; struct pf_fragment *frag; pf_ip2key(&key, ip); frag = RB_FIND(pf_frag_tree, tree, &key); if (frag != NULL) { /* XXX Are we sure we want to update the timeout? */ frag->fr_timeout = time_second; if (BUFFER_FRAGMENTS(frag)) { TAILQ_REMOVE(&pf_fragqueue, frag, frag_next); TAILQ_INSERT_HEAD(&pf_fragqueue, frag, frag_next); } else { TAILQ_REMOVE(&pf_cachequeue, frag, frag_next); TAILQ_INSERT_HEAD(&pf_cachequeue, frag, frag_next); } } return (frag); } /* Removes a fragment from the fragment queue and frees the fragment */ void pf_remove_fragment(struct pf_fragment *frag) { if (BUFFER_FRAGMENTS(frag)) { RB_REMOVE(pf_frag_tree, &pf_frag_tree, frag); TAILQ_REMOVE(&pf_fragqueue, frag, frag_next); pool_put(&pf_frag_pl, frag); } else { RB_REMOVE(pf_frag_tree, &pf_cache_tree, frag); TAILQ_REMOVE(&pf_cachequeue, frag, frag_next); pool_put(&pf_cache_pl, frag); } } #define FR_IP_OFF(fr) ((ntohs((fr)->fr_ip->ip_off) & IP_OFFMASK) << 3) struct mbuf * pf_reassemble(struct mbuf **m0, struct pf_fragment **frag, struct pf_frent *frent, int mff) { struct mbuf *m = *m0, *m2; struct pf_frent *frea, *next; struct pf_frent *frep = NULL; struct ip *ip = frent->fr_ip; int hlen = ip->ip_hl << 2; u_int16_t off = (ntohs(ip->ip_off) & IP_OFFMASK) << 3; u_int16_t ip_len = ntohs(ip->ip_len) - ip->ip_hl * 4; u_int16_t max = ip_len + off; KASSERT(*frag == NULL || BUFFER_FRAGMENTS(*frag)); /* Strip off ip header */ m->m_data += hlen; m->m_len -= hlen; /* Create a new reassembly queue for this packet */ if (*frag == NULL) { *frag = pool_get(&pf_frag_pl, PR_NOWAIT); if (*frag == NULL) { pf_flush_fragments(); *frag = pool_get(&pf_frag_pl, PR_NOWAIT); if (*frag == NULL) goto drop_fragment; } (*frag)->fr_flags = 0; (*frag)->fr_max = 0; (*frag)->fr_src = frent->fr_ip->ip_src; (*frag)->fr_dst = frent->fr_ip->ip_dst; (*frag)->fr_p = frent->fr_ip->ip_p; (*frag)->fr_id = frent->fr_ip->ip_id; (*frag)->fr_timeout = time_second; LIST_INIT(&(*frag)->fr_queue); RB_INSERT(pf_frag_tree, &pf_frag_tree, *frag); TAILQ_INSERT_HEAD(&pf_fragqueue, *frag, frag_next); /* We do not have a previous fragment */ frep = NULL; goto insert; } /* * Find a fragment after the current one: * - off contains the real shifted offset. */ LIST_FOREACH(frea, &(*frag)->fr_queue, fr_next) { if (FR_IP_OFF(frea) > off) break; frep = frea; } KASSERT(frep != NULL || frea != NULL); if (frep != NULL && FR_IP_OFF(frep) + ntohs(frep->fr_ip->ip_len) - frep->fr_ip->ip_hl * 4 > off) { u_int16_t precut; precut = FR_IP_OFF(frep) + ntohs(frep->fr_ip->ip_len) - frep->fr_ip->ip_hl * 4 - off; if (precut >= ip_len) goto drop_fragment; m_adj(frent->fr_m, precut); DPFPRINTF(("overlap -%d\n", precut)); /* Enforce 8 byte boundaries */ ip->ip_off = htons(ntohs(ip->ip_off) + (precut >> 3)); off = (ntohs(ip->ip_off) & IP_OFFMASK) << 3; ip_len -= precut; ip->ip_len = htons(ip_len); } for (; frea != NULL && ip_len + off > FR_IP_OFF(frea); frea = next) { u_int16_t aftercut; aftercut = ip_len + off - FR_IP_OFF(frea); DPFPRINTF(("adjust overlap %d\n", aftercut)); if (aftercut < ntohs(frea->fr_ip->ip_len) - frea->fr_ip->ip_hl * 4) { frea->fr_ip->ip_len = htons(ntohs(frea->fr_ip->ip_len) - aftercut); frea->fr_ip->ip_off = htons(ntohs(frea->fr_ip->ip_off) + (aftercut >> 3)); m_adj(frea->fr_m, aftercut); break; } /* This fragment is completely overlapped, lose it */ next = LIST_NEXT(frea, fr_next); m_freem(frea->fr_m); LIST_REMOVE(frea, fr_next); pool_put(&pf_frent_pl, frea); pf_nfrents--; } insert: /* Update maximum data size */ if ((*frag)->fr_max < max) (*frag)->fr_max = max; /* This is the last segment */ if (!mff) (*frag)->fr_flags |= PFFRAG_SEENLAST; if (frep == NULL) LIST_INSERT_HEAD(&(*frag)->fr_queue, frent, fr_next); else LIST_INSERT_AFTER(frep, frent, fr_next); /* Check if we are completely reassembled */ if (!((*frag)->fr_flags & PFFRAG_SEENLAST)) return (NULL); /* Check if we have all the data */ off = 0; for (frep = LIST_FIRST(&(*frag)->fr_queue); frep; frep = next) { next = LIST_NEXT(frep, fr_next); off += ntohs(frep->fr_ip->ip_len) - frep->fr_ip->ip_hl * 4; if (off < (*frag)->fr_max && (next == NULL || FR_IP_OFF(next) != off)) { DPFPRINTF(("missing fragment at %d, next %d, max %d\n", off, next == NULL ? -1 : FR_IP_OFF(next), (*frag)->fr_max)); return (NULL); } } DPFPRINTF(("%d < %d?\n", off, (*frag)->fr_max)); if (off < (*frag)->fr_max) return (NULL); /* We have all the data */ frent = LIST_FIRST(&(*frag)->fr_queue); KASSERT(frent != NULL); if ((frent->fr_ip->ip_hl << 2) + off > IP_MAXPACKET) { DPFPRINTF(("drop: too big: %d\n", off)); pf_free_fragment(*frag); *frag = NULL; return (NULL); } next = LIST_NEXT(frent, fr_next); /* Magic from ip_input */ ip = frent->fr_ip; m = frent->fr_m; m2 = m->m_next; m->m_next = NULL; m_cat(m, m2); pool_put(&pf_frent_pl, frent); pf_nfrents--; for (frent = next; frent != NULL; frent = next) { next = LIST_NEXT(frent, fr_next); m2 = frent->fr_m; pool_put(&pf_frent_pl, frent); pf_nfrents--; m_cat(m, m2); } ip->ip_src = (*frag)->fr_src; ip->ip_dst = (*frag)->fr_dst; /* Remove from fragment queue */ pf_remove_fragment(*frag); *frag = NULL; hlen = ip->ip_hl << 2; ip->ip_len = htons(off + hlen); m->m_len += hlen; m->m_data -= hlen; /* some debugging cruft by sklower, below, will go away soon */ /* XXX this should be done elsewhere */ if (m->m_flags & M_PKTHDR) { int plen = 0; for (m2 = m; m2; m2 = m2->m_next) plen += m2->m_len; m->m_pkthdr.len = plen; } DPFPRINTF(("complete: %p(%d)\n", m, ntohs(ip->ip_len))); return (m); drop_fragment: /* Oops - fail safe - drop packet */ pool_put(&pf_frent_pl, frent); pf_nfrents--; m_freem(m); return (NULL); } int pf_normalize_ip(struct mbuf **m0, int dir, struct pfi_kif *kif, u_short *reason, struct pf_pdesc *pd) { struct mbuf *m = *m0; struct pf_frent *frent; struct pf_fragment *frag = NULL; struct ip *h = mtod(m, struct ip *); int mff = (ntohs(h->ip_off) & IP_MF); int hlen = h->ip_hl << 2; u_int16_t fragoff = (ntohs(h->ip_off) & IP_OFFMASK) << 3; u_int16_t max; int ip_len; int ip_off; /* Check for illegal packets */ if (hlen < (int)sizeof(struct ip)) goto drop; if (hlen > ntohs(h->ip_len)) goto drop; /* Clear IP_DF if we're in no-df mode */ if (!(pf_status.reass & PF_REASS_NODF) && h->ip_off & htons(IP_DF)) { u_int16_t ip_off = h->ip_off; h->ip_off &= htons(~IP_DF); h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_off, h->ip_off, 0); } /* We will need other tests here */ if (!fragoff && !mff) goto no_fragment; /* We're dealing with a fragment now. Don't allow fragments * with IP_DF to enter the cache. If the flag was cleared by * no-df above, fine. Otherwise drop it. */ if (h->ip_off & htons(IP_DF)) { DPFPRINTF(("IP_DF\n")); goto bad; } ip_len = ntohs(h->ip_len) - hlen; ip_off = (ntohs(h->ip_off) & IP_OFFMASK) << 3; /* All fragments are 8 byte aligned */ if (mff && (ip_len & 0x7)) { DPFPRINTF(("mff and %d\n", ip_len)); goto bad; } /* Respect maximum length */ if (fragoff + ip_len > IP_MAXPACKET) { DPFPRINTF(("max packet %d\n", fragoff + ip_len)); goto bad; } max = fragoff + ip_len; /* Fully buffer all of the fragments */ frag = pf_find_fragment(h, &pf_frag_tree); /* Check if we saw the last fragment already */ if (frag != NULL && (frag->fr_flags & PFFRAG_SEENLAST) && max > frag->fr_max) goto bad; /* Get an entry for the fragment queue */ frent = pool_get(&pf_frent_pl, PR_NOWAIT); if (frent == NULL) { REASON_SET(reason, PFRES_MEMORY); return (PF_DROP); } pf_nfrents++; frent->fr_ip = h; frent->fr_m = m; /* Might return a completely reassembled mbuf, or NULL */ DPFPRINTF(("reass frag %d @ %d-%d\n", h->ip_id, fragoff, max)); *m0 = m = pf_reassemble(m0, &frag, frent, mff); if (m == NULL) return (PF_DROP); if (frag != NULL && (frag->fr_flags & PFFRAG_DROP)) goto drop; h = mtod(m, struct ip *); no_fragment: /* At this point, only IP_DF is allowed in ip_off */ if (h->ip_off & ~htons(IP_DF)) { u_int16_t ip_off = h->ip_off; h->ip_off &= htons(IP_DF); h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_off, h->ip_off, 0); } pd->flags |= PFDESC_IP_REAS; return (PF_PASS); drop: REASON_SET(reason, PFRES_NORM); return (PF_DROP); bad: DPFPRINTF(("dropping bad fragment\n")); /* Free associated fragments */ if (frag != NULL) pf_free_fragment(frag); REASON_SET(reason, PFRES_FRAG); return (PF_DROP); } #ifdef INET6 int pf_normalize_ip6(struct mbuf **m0, int dir, struct pfi_kif *kif, u_short *reason, struct pf_pdesc *pd) { struct mbuf *m = *m0; struct ip6_hdr *h = mtod(m, struct ip6_hdr *); int off; struct ip6_ext ext; struct ip6_opt opt; struct ip6_opt_jumbo jumbo; struct ip6_frag frag; u_int32_t jumbolen = 0, plen; u_int16_t fragoff = 0; int optend; int ooff; u_int8_t proto; int terminal; /* Check for illegal packets */ if (sizeof(struct ip6_hdr) + IPV6_MAXPACKET < m->m_pkthdr.len) goto drop; off = sizeof(struct ip6_hdr); proto = h->ip6_nxt; terminal = 0; do { switch (proto) { case IPPROTO_FRAGMENT: goto fragment; break; case IPPROTO_AH: case IPPROTO_ROUTING: case IPPROTO_DSTOPTS: if (!pf_pull_hdr(m, off, &ext, sizeof(ext), NULL, NULL, AF_INET6)) goto shortpkt; if (proto == IPPROTO_AH) off += (ext.ip6e_len + 2) * 4; else off += (ext.ip6e_len + 1) * 8; proto = ext.ip6e_nxt; break; case IPPROTO_HOPOPTS: if (!pf_pull_hdr(m, off, &ext, sizeof(ext), NULL, NULL, AF_INET6)) goto shortpkt; optend = off + (ext.ip6e_len + 1) * 8; ooff = off + sizeof(ext); do { if (!pf_pull_hdr(m, ooff, &opt.ip6o_type, sizeof(opt.ip6o_type), NULL, NULL, AF_INET6)) goto shortpkt; if (opt.ip6o_type == IP6OPT_PAD1) { ooff++; continue; } if (!pf_pull_hdr(m, ooff, &opt, sizeof(opt), NULL, NULL, AF_INET6)) goto shortpkt; if (ooff + sizeof(opt) + opt.ip6o_len > optend) goto drop; switch (opt.ip6o_type) { case IP6OPT_JUMBO: if (h->ip6_plen != 0) goto drop; if (!pf_pull_hdr(m, ooff, &jumbo, sizeof(jumbo), NULL, NULL, AF_INET6)) goto shortpkt; memcpy(&jumbolen, jumbo.ip6oj_jumbo_len, sizeof(jumbolen)); jumbolen = ntohl(jumbolen); if (jumbolen <= IPV6_MAXPACKET) goto drop; if (sizeof(struct ip6_hdr) + jumbolen != m->m_pkthdr.len) goto drop; break; default: break; } ooff += sizeof(opt) + opt.ip6o_len; } while (ooff < optend); off = optend; proto = ext.ip6e_nxt; break; default: terminal = 1; break; } } while (!terminal); /* jumbo payload option must be present, or plen > 0 */ if (ntohs(h->ip6_plen) == 0) plen = jumbolen; else plen = ntohs(h->ip6_plen); if (plen == 0) goto drop; if (sizeof(struct ip6_hdr) + plen > m->m_pkthdr.len) goto shortpkt; return (PF_PASS); fragment: if (ntohs(h->ip6_plen) == 0 || jumbolen) goto drop; plen = ntohs(h->ip6_plen); if (!pf_pull_hdr(m, off, &frag, sizeof(frag), NULL, NULL, AF_INET6)) goto shortpkt; fragoff = ntohs(frag.ip6f_offlg & IP6F_OFF_MASK); if (fragoff + (plen - off - sizeof(frag)) > IPV6_MAXPACKET) goto badfrag; /* do something about it */ /* remember to set pd->flags |= PFDESC_IP_REAS */ return (PF_PASS); shortpkt: REASON_SET(reason, PFRES_SHORT); return (PF_DROP); drop: REASON_SET(reason, PFRES_NORM); return (PF_DROP); badfrag: REASON_SET(reason, PFRES_FRAG); return (PF_DROP); } #endif /* INET6 */ int pf_normalize_tcp(int dir, struct pfi_kif *kif, struct mbuf *m, int ipoff, int off, void *h, struct pf_pdesc *pd) { struct tcphdr *th = pd->hdr.tcp; u_short reason; u_int8_t flags; u_int rewrite = 0; flags = th->th_flags; if (flags & TH_SYN) { /* Illegal packet */ if (flags & TH_RST) goto tcp_drop; if (flags & TH_FIN) flags &= ~TH_FIN; } else { /* Illegal packet */ if (!(flags & (TH_ACK|TH_RST))) goto tcp_drop; } if (!(flags & TH_ACK)) { /* These flags are only valid if ACK is set */ if ((flags & TH_FIN) || (flags & TH_PUSH) || (flags & TH_URG)) goto tcp_drop; } /* Check for illegal header length */ if (th->th_off < (sizeof(struct tcphdr) >> 2)) goto tcp_drop; /* If flags changed, or reserved data set, then adjust */ if (flags != th->th_flags || th->th_x2 != 0) { u_int16_t ov, nv; ov = *(u_int16_t *)(&th->th_ack + 1); th->th_flags = flags; th->th_x2 = 0; nv = *(u_int16_t *)(&th->th_ack + 1); th->th_sum = pf_cksum_fixup(th->th_sum, ov, nv, 0); rewrite = 1; } /* Remove urgent pointer, if TH_URG is not set */ if (!(flags & TH_URG) && th->th_urp) { th->th_sum = pf_cksum_fixup(th->th_sum, th->th_urp, 0, 0); th->th_urp = 0; rewrite = 1; } /* copy back packet headers if we sanitized */ if (rewrite) m_copyback(m, off, sizeof(*th), th); return (PF_PASS); tcp_drop: REASON_SET(&reason, PFRES_NORM); return (PF_DROP); } int pf_normalize_tcp_init(struct mbuf *m, int off, struct pf_pdesc *pd, struct tcphdr *th, struct pf_state_peer *src, struct pf_state_peer *dst) { u_int32_t tsval, tsecr; u_int8_t hdr[60]; u_int8_t *opt; KASSERT(src->scrub == NULL); src->scrub = pool_get(&pf_state_scrub_pl, PR_NOWAIT); if (src->scrub == NULL) return (1); bzero(src->scrub, sizeof(*src->scrub)); switch (pd->af) { #ifdef INET case AF_INET: { struct ip *h = mtod(m, struct ip *); src->scrub->pfss_ttl = h->ip_ttl; break; } #endif /* INET */ #ifdef INET6 case AF_INET6: { struct ip6_hdr *h = mtod(m, struct ip6_hdr *); src->scrub->pfss_ttl = h->ip6_hlim; break; } #endif /* INET6 */ } /* * All normalizations below are only begun if we see the start of * the connections. They must all set an enabled bit in pfss_flags */ if ((th->th_flags & TH_SYN) == 0) return (0); if (th->th_off > (sizeof(struct tcphdr) >> 2) && src->scrub && pf_pull_hdr(m, off, hdr, th->th_off << 2, NULL, NULL, pd->af)) { /* Diddle with TCP options */ int hlen; opt = hdr + sizeof(struct tcphdr); hlen = (th->th_off << 2) - sizeof(struct tcphdr); while (hlen >= TCPOLEN_TIMESTAMP) { switch (*opt) { case TCPOPT_EOL: /* FALLTHROUGH */ case TCPOPT_NOP: opt++; hlen--; break; case TCPOPT_TIMESTAMP: if (opt[1] >= TCPOLEN_TIMESTAMP) { src->scrub->pfss_flags |= PFSS_TIMESTAMP; src->scrub->pfss_ts_mod = htonl(arc4random()); /* note PFSS_PAWS not set yet */ memcpy(&tsval, &opt[2], sizeof(u_int32_t)); memcpy(&tsecr, &opt[6], sizeof(u_int32_t)); src->scrub->pfss_tsval0 = ntohl(tsval); src->scrub->pfss_tsval = ntohl(tsval); src->scrub->pfss_tsecr = ntohl(tsecr); getmicrouptime(&src->scrub->pfss_last); } /* FALLTHROUGH */ default: hlen -= MAX(opt[1], 2); opt += MAX(opt[1], 2); break; } } } return (0); } void pf_normalize_tcp_cleanup(struct pf_state *state) { if (state->src.scrub) pool_put(&pf_state_scrub_pl, state->src.scrub); if (state->dst.scrub) pool_put(&pf_state_scrub_pl, state->dst.scrub); /* Someday... flush the TCP segment reassembly descriptors. */ } int pf_normalize_tcp_stateful(struct mbuf *m, int off, struct pf_pdesc *pd, u_short *reason, struct tcphdr *th, struct pf_state *state, struct pf_state_peer *src, struct pf_state_peer *dst, int *writeback) { struct timeval uptime; u_int32_t tsval, tsecr; u_int tsval_from_last; u_int8_t hdr[60]; u_int8_t *opt; int copyback = 0; int got_ts = 0; KASSERT(src->scrub || dst->scrub); /* * Enforce the minimum TTL seen for this connection. Negate a common * technique to evade an intrusion detection system and confuse * firewall state code. */ switch (pd->af) { #ifdef INET case AF_INET: { if (src->scrub) { struct ip *h = mtod(m, struct ip *); if (h->ip_ttl > src->scrub->pfss_ttl) src->scrub->pfss_ttl = h->ip_ttl; h->ip_ttl = src->scrub->pfss_ttl; } break; } #endif /* INET */ #ifdef INET6 case AF_INET6: { if (src->scrub) { struct ip6_hdr *h = mtod(m, struct ip6_hdr *); if (h->ip6_hlim > src->scrub->pfss_ttl) src->scrub->pfss_ttl = h->ip6_hlim; h->ip6_hlim = src->scrub->pfss_ttl; } break; } #endif /* INET6 */ } if (th->th_off > (sizeof(struct tcphdr) >> 2) && ((src->scrub && (src->scrub->pfss_flags & PFSS_TIMESTAMP)) || (dst->scrub && (dst->scrub->pfss_flags & PFSS_TIMESTAMP))) && pf_pull_hdr(m, off, hdr, th->th_off << 2, NULL, NULL, pd->af)) { /* Diddle with TCP options */ int hlen; opt = hdr + sizeof(struct tcphdr); hlen = (th->th_off << 2) - sizeof(struct tcphdr); while (hlen >= TCPOLEN_TIMESTAMP) { switch (*opt) { case TCPOPT_EOL: /* FALLTHROUGH */ case TCPOPT_NOP: opt++; hlen--; break; case TCPOPT_TIMESTAMP: /* Modulate the timestamps. Can be used for * NAT detection, OS uptime determination or * reboot detection. */ if (got_ts) { /* Huh? Multiple timestamps!? */ if (pf_status.debug >= PF_DEBUG_MISC) { DPFPRINTF(("multiple TS??")); pf_print_state(state); printf("\n"); } REASON_SET(reason, PFRES_TS); return (PF_DROP); } if (opt[1] >= TCPOLEN_TIMESTAMP) { memcpy(&tsval, &opt[2], sizeof(u_int32_t)); if (tsval && src->scrub && (src->scrub->pfss_flags & PFSS_TIMESTAMP)) { tsval = ntohl(tsval); pf_change_a(&opt[2], &th->th_sum, htonl(tsval + src->scrub->pfss_ts_mod), 0); copyback = 1; } /* Modulate TS reply iff valid (!0) */ memcpy(&tsecr, &opt[6], sizeof(u_int32_t)); if (tsecr && dst->scrub && (dst->scrub->pfss_flags & PFSS_TIMESTAMP)) { tsecr = ntohl(tsecr) - dst->scrub->pfss_ts_mod; pf_change_a(&opt[6], &th->th_sum, htonl(tsecr), 0); copyback = 1; } got_ts = 1; } /* FALLTHROUGH */ default: hlen -= MAX(opt[1], 2); opt += MAX(opt[1], 2); break; } } if (copyback) { /* Copyback the options, caller copys back header */ *writeback = 1; m_copyback(m, off + sizeof(struct tcphdr), (th->th_off << 2) - sizeof(struct tcphdr), hdr + sizeof(struct tcphdr)); } } /* * Must invalidate PAWS checks on connections idle for too long. * The fastest allowed timestamp clock is 1ms. That turns out to * be about 24 days before it wraps. XXX Right now our lowerbound * TS echo check only works for the first 12 days of a connection * when the TS has exhausted half its 32bit space */ #define TS_MAX_IDLE (24*24*60*60) #define TS_MAX_CONN (12*24*60*60) /* XXX remove when better tsecr check */ getmicrouptime(&uptime); if (src->scrub && (src->scrub->pfss_flags & PFSS_PAWS) && (uptime.tv_sec - src->scrub->pfss_last.tv_sec > TS_MAX_IDLE || time_second - state->creation > TS_MAX_CONN)) { if (pf_status.debug >= PF_DEBUG_MISC) { DPFPRINTF(("src idled out of PAWS\n")); pf_print_state(state); printf("\n"); } src->scrub->pfss_flags = (src->scrub->pfss_flags & ~PFSS_PAWS) | PFSS_PAWS_IDLED; } if (dst->scrub && (dst->scrub->pfss_flags & PFSS_PAWS) && uptime.tv_sec - dst->scrub->pfss_last.tv_sec > TS_MAX_IDLE) { if (pf_status.debug >= PF_DEBUG_MISC) { DPFPRINTF(("dst idled out of PAWS\n")); pf_print_state(state); printf("\n"); } dst->scrub->pfss_flags = (dst->scrub->pfss_flags & ~PFSS_PAWS) | PFSS_PAWS_IDLED; } if (got_ts && src->scrub && dst->scrub && (src->scrub->pfss_flags & PFSS_PAWS) && (dst->scrub->pfss_flags & PFSS_PAWS)) { /* Validate that the timestamps are "in-window". * RFC1323 describes TCP Timestamp options that allow * measurement of RTT (round trip time) and PAWS * (protection against wrapped sequence numbers). PAWS * gives us a set of rules for rejecting packets on * long fat pipes (packets that were somehow delayed * in transit longer than the time it took to send the * full TCP sequence space of 4Gb). We can use these * rules and infer a few others that will let us treat * the 32bit timestamp and the 32bit echoed timestamp * as sequence numbers to prevent a blind attacker from * inserting packets into a connection. * * RFC1323 tells us: * - The timestamp on this packet must be greater than * or equal to the last value echoed by the other * endpoint. The RFC says those will be discarded * since it is a dup that has already been acked. * This gives us a lowerbound on the timestamp. * timestamp >= other last echoed timestamp * - The timestamp will be less than or equal to * the last timestamp plus the time between the * last packet and now. The RFC defines the max * clock rate as 1ms. We will allow clocks to be * up to 10% fast and will allow a total difference * or 30 seconds due to a route change. And this * gives us an upperbound on the timestamp. * timestamp <= last timestamp + max ticks * We have to be careful here. Windows will send an * initial timestamp of zero and then initialize it * to a random value after the 3whs; presumably to * avoid a DoS by having to call an expensive RNG * during a SYN flood. Proof MS has at least one * good security geek. * * - The TCP timestamp option must also echo the other * endpoints timestamp. The timestamp echoed is the * one carried on the earliest unacknowledged segment * on the left edge of the sequence window. The RFC * states that the host will reject any echoed * timestamps that were larger than any ever sent. * This gives us an upperbound on the TS echo. * tescr <= largest_tsval * - The lowerbound on the TS echo is a little more * tricky to determine. The other endpoint's echoed * values will not decrease. But there may be * network conditions that re-order packets and * cause our view of them to decrease. For now the * only lowerbound we can safely determine is that * the TS echo will never be less than the original * TS. XXX There is probably a better lowerbound. * Remove TS_MAX_CONN with better lowerbound check. * tescr >= other original TS * * It is also important to note that the fastest * timestamp clock of 1ms will wrap its 32bit space in * 24 days. So we just disable TS checking after 24 * days of idle time. We actually must use a 12d * connection limit until we can come up with a better * lowerbound to the TS echo check. */ struct timeval delta_ts; int ts_fudge; /* * PFTM_TS_DIFF is how many seconds of leeway to allow * a host's timestamp. This can happen if the previous * packet got delayed in transit for much longer than * this packet. */ if ((ts_fudge = state->rule.ptr->timeout[PFTM_TS_DIFF]) == 0) ts_fudge = pf_default_rule.timeout[PFTM_TS_DIFF]; /* Calculate max ticks since the last timestamp */ #define TS_MAXFREQ 1100 /* RFC max TS freq of 1Khz + 10% skew */ #define TS_MICROSECS 1000000 /* microseconds per second */ timersub(&uptime, &src->scrub->pfss_last, &delta_ts); tsval_from_last = (delta_ts.tv_sec + ts_fudge) * TS_MAXFREQ; tsval_from_last += delta_ts.tv_usec / (TS_MICROSECS/TS_MAXFREQ); if ((src->state >= TCPS_ESTABLISHED && dst->state >= TCPS_ESTABLISHED) && (SEQ_LT(tsval, dst->scrub->pfss_tsecr) || SEQ_GT(tsval, src->scrub->pfss_tsval + tsval_from_last) || (tsecr && (SEQ_GT(tsecr, dst->scrub->pfss_tsval) || SEQ_LT(tsecr, dst->scrub->pfss_tsval0))))) { /* Bad RFC1323 implementation or an insertion attack. * * - Solaris 2.6 and 2.7 are known to send another ACK * after the FIN,FIN|ACK,ACK closing that carries * an old timestamp. */ DPFPRINTF(("Timestamp failed %c%c%c%c\n", SEQ_LT(tsval, dst->scrub->pfss_tsecr) ? '0' : ' ', SEQ_GT(tsval, src->scrub->pfss_tsval + tsval_from_last) ? '1' : ' ', SEQ_GT(tsecr, dst->scrub->pfss_tsval) ? '2' : ' ', SEQ_LT(tsecr, dst->scrub->pfss_tsval0)? '3' : ' ')); DPFPRINTF((" tsval: %lu tsecr: %lu +ticks: %lu " "idle: %lus %lums\n", tsval, tsecr, tsval_from_last, delta_ts.tv_sec, delta_ts.tv_usec / 1000)); DPFPRINTF((" src->tsval: %lu tsecr: %lu\n", src->scrub->pfss_tsval, src->scrub->pfss_tsecr)); DPFPRINTF((" dst->tsval: %lu tsecr: %lu tsval0: %lu" "\n", dst->scrub->pfss_tsval, dst->scrub->pfss_tsecr, dst->scrub->pfss_tsval0)); if (pf_status.debug >= PF_DEBUG_MISC) { pf_print_state(state); pf_print_flags(th->th_flags); printf("\n"); } REASON_SET(reason, PFRES_TS); return (PF_DROP); } /* XXX I'd really like to require tsecr but it's optional */ } else if (!got_ts && (th->th_flags & TH_RST) == 0 && ((src->state == TCPS_ESTABLISHED && dst->state == TCPS_ESTABLISHED) || pd->p_len > 0 || (th->th_flags & TH_SYN)) && src->scrub && dst->scrub && (src->scrub->pfss_flags & PFSS_PAWS) && (dst->scrub->pfss_flags & PFSS_PAWS)) { /* Didn't send a timestamp. Timestamps aren't really useful * when: * - connection opening or closing (often not even sent). * but we must not let an attacker to put a FIN on a * data packet to sneak it through our ESTABLISHED check. * - on a TCP reset. RFC suggests not even looking at TS. * - on an empty ACK. The TS will not be echoed so it will * probably not help keep the RTT calculation in sync and * there isn't as much danger when the sequence numbers * got wrapped. So some stacks don't include TS on empty * ACKs :-( * * To minimize the disruption to mostly RFC1323 conformant * stacks, we will only require timestamps on data packets. * * And what do ya know, we cannot require timestamps on data * packets. There appear to be devices that do legitimate * TCP connection hijacking. There are HTTP devices that allow * a 3whs (with timestamps) and then buffer the HTTP request. * If the intermediate device has the HTTP response cache, it * will spoof the response but not bother timestamping its * packets. So we can look for the presence of a timestamp in * the first data packet and if there, require it in all future * packets. */ if (pd->p_len > 0 && (src->scrub->pfss_flags & PFSS_DATA_TS)) { /* * Hey! Someone tried to sneak a packet in. Or the * stack changed its RFC1323 behavior?!?! */ if (pf_status.debug >= PF_DEBUG_MISC) { DPFPRINTF(("Did not receive expected RFC1323 " "timestamp\n")); pf_print_state(state); pf_print_flags(th->th_flags); printf("\n"); } REASON_SET(reason, PFRES_TS); return (PF_DROP); } } /* * We will note if a host sends his data packets with or without * timestamps. And require all data packets to contain a timestamp * if the first does. PAWS implicitly requires that all data packets be * timestamped. But I think there are middle-man devices that hijack * TCP streams immediately after the 3whs and don't timestamp their * packets (seen in a WWW accelerator or cache). */ if (pd->p_len > 0 && src->scrub && (src->scrub->pfss_flags & (PFSS_TIMESTAMP|PFSS_DATA_TS|PFSS_DATA_NOTS)) == PFSS_TIMESTAMP) { if (got_ts) src->scrub->pfss_flags |= PFSS_DATA_TS; else { src->scrub->pfss_flags |= PFSS_DATA_NOTS; if (pf_status.debug >= PF_DEBUG_MISC && dst->scrub && (dst->scrub->pfss_flags & PFSS_TIMESTAMP)) { /* Don't warn if other host rejected RFC1323 */ DPFPRINTF(("Broken RFC1323 stack did not " "timestamp data packet. Disabled PAWS " "security.\n")); pf_print_state(state); pf_print_flags(th->th_flags); printf("\n"); } } } /* * Update PAWS values */ if (got_ts && src->scrub && PFSS_TIMESTAMP == (src->scrub->pfss_flags & (PFSS_PAWS_IDLED|PFSS_TIMESTAMP))) { getmicrouptime(&src->scrub->pfss_last); if (SEQ_GEQ(tsval, src->scrub->pfss_tsval) || (src->scrub->pfss_flags & PFSS_PAWS) == 0) src->scrub->pfss_tsval = tsval; if (tsecr) { if (SEQ_GEQ(tsecr, src->scrub->pfss_tsecr) || (src->scrub->pfss_flags & PFSS_PAWS) == 0) src->scrub->pfss_tsecr = tsecr; if ((src->scrub->pfss_flags & PFSS_PAWS) == 0 && (SEQ_LT(tsval, src->scrub->pfss_tsval0) || src->scrub->pfss_tsval0 == 0)) { /* tsval0 MUST be the lowest timestamp */ src->scrub->pfss_tsval0 = tsval; } /* Only fully initialized after a TS gets echoed */ if ((src->scrub->pfss_flags & PFSS_PAWS) == 0) src->scrub->pfss_flags |= PFSS_PAWS; } } /* I have a dream.... TCP segment reassembly.... */ return (0); } int pf_normalize_mss(struct mbuf *m, int off, struct pf_pdesc *pd, u_int16_t maxmss) { struct tcphdr *th = pd->hdr.tcp; u_int16_t *mss; int thoff; int opt, cnt, optlen = 0; u_char opts[MAX_TCPOPTLEN]; u_char *optp = opts; thoff = th->th_off << 2; cnt = thoff - sizeof(struct tcphdr); if (cnt > 0 && !pf_pull_hdr(m, off + sizeof(*th), opts, cnt, NULL, NULL, pd->af)) return (0); for (; cnt > 0; cnt -= optlen, optp += optlen) { opt = optp[0]; if (opt == TCPOPT_EOL) break; if (opt == TCPOPT_NOP) optlen = 1; else { if (cnt < 2) break; optlen = optp[1]; if (optlen < 2 || optlen > cnt) break; } switch (opt) { case TCPOPT_MAXSEG: mss = (u_int16_t *)(optp + 2); if ((ntohs(*mss)) > maxmss) { th->th_sum = pf_cksum_fixup(th->th_sum, *mss, htons(maxmss), 0); *mss = htons(maxmss); m_copyback(m, off + sizeof(*th), thoff - sizeof(*th), opts); m_copyback(m, off, sizeof(*th), th); } break; default: break; } } return (0); } void pf_scrub_ip(struct mbuf **m0, u_int16_t flags, u_int8_t min_ttl, u_int8_t tos) { struct mbuf *m = *m0; struct ip *h = mtod(m, struct ip *); /* Clear IP_DF if no-df was requested */ if (flags & PFSTATE_NODF && h->ip_off & htons(IP_DF)) { u_int16_t ip_off = h->ip_off; h->ip_off &= htons(~IP_DF); h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_off, h->ip_off, 0); } /* Enforce a minimum ttl, may cause endless packet loops */ if (min_ttl && h->ip_ttl < min_ttl) { u_int16_t ip_ttl = h->ip_ttl; h->ip_ttl = min_ttl; h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_ttl, h->ip_ttl, 0); } /* Enforce tos */ if (flags & PFSTATE_SETTOS) { u_int16_t ov, nv; ov = *(u_int16_t *)h; h->ip_tos = tos; nv = *(u_int16_t *)h; h->ip_sum = pf_cksum_fixup(h->ip_sum, ov, nv, 0); } /* random-id, but not for fragments */ if (flags & PFSTATE_RANDOMID && !(h->ip_off & ~htons(IP_DF))) { u_int16_t ip_id = h->ip_id; h->ip_id = ip_randomid(); h->ip_sum = pf_cksum_fixup(h->ip_sum, ip_id, h->ip_id, 0); } } #ifdef INET6 void pf_scrub_ip6(struct mbuf **m0, u_int8_t min_ttl) { struct mbuf *m = *m0; struct ip6_hdr *h = mtod(m, struct ip6_hdr *); /* Enforce a minimum ttl, may cause endless packet loops */ if (min_ttl && h->ip6_hlim < min_ttl) h->ip6_hlim = min_ttl; } #endif