diff options
Diffstat (limited to 'net/netfilter/nf_nat_helper.c')
| -rw-r--r-- | net/netfilter/nf_nat_helper.c | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/net/netfilter/nf_nat_helper.c b/net/netfilter/nf_nat_helper.c new file mode 100644 index 000000000..a95a25196 --- /dev/null +++ b/net/netfilter/nf_nat_helper.c @@ -0,0 +1,231 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* nf_nat_helper.c - generic support functions for NAT helpers + * + * (C) 2000-2002 Harald Welte <laforge@netfilter.org> + * (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org> + * (C) 2007-2012 Patrick McHardy <kaber@trash.net> + */ +#include <linux/module.h> +#include <linux/gfp.h> +#include <linux/types.h> +#include <linux/skbuff.h> +#include <linux/tcp.h> +#include <linux/udp.h> +#include <net/tcp.h> + +#include <net/netfilter/nf_conntrack.h> +#include <net/netfilter/nf_conntrack_helper.h> +#include <net/netfilter/nf_conntrack_ecache.h> +#include <net/netfilter/nf_conntrack_expect.h> +#include <net/netfilter/nf_conntrack_seqadj.h> +#include <net/netfilter/nf_nat.h> +#include <net/netfilter/nf_nat_helper.h> + +/* Frobs data inside this packet, which is linear. */ +static void mangle_contents(struct sk_buff *skb, + unsigned int dataoff, + unsigned int match_offset, + unsigned int match_len, + const char *rep_buffer, + unsigned int rep_len) +{ + unsigned char *data; + + SKB_LINEAR_ASSERT(skb); + data = skb_network_header(skb) + dataoff; + + /* move post-replacement */ + memmove(data + match_offset + rep_len, + data + match_offset + match_len, + skb_tail_pointer(skb) - (skb_network_header(skb) + dataoff + + match_offset + match_len)); + + /* insert data from buffer */ + memcpy(data + match_offset, rep_buffer, rep_len); + + /* update skb info */ + if (rep_len > match_len) { + pr_debug("nf_nat_mangle_packet: Extending packet by " + "%u from %u bytes\n", rep_len - match_len, skb->len); + skb_put(skb, rep_len - match_len); + } else { + pr_debug("nf_nat_mangle_packet: Shrinking packet from " + "%u from %u bytes\n", match_len - rep_len, skb->len); + __skb_trim(skb, skb->len + rep_len - match_len); + } + + if (nf_ct_l3num((struct nf_conn *)skb_nfct(skb)) == NFPROTO_IPV4) { + /* fix IP hdr checksum information */ + ip_hdr(skb)->tot_len = htons(skb->len); + ip_send_check(ip_hdr(skb)); + } else + ipv6_hdr(skb)->payload_len = + htons(skb->len - sizeof(struct ipv6hdr)); +} + +/* Unusual, but possible case. */ +static bool enlarge_skb(struct sk_buff *skb, unsigned int extra) +{ + if (skb->len + extra > 65535) + return false; + + if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC)) + return false; + + return true; +} + +/* Generic function for mangling variable-length address changes inside + * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX + * command in FTP). + * + * Takes care about all the nasty sequence number changes, checksumming, + * skb enlargement, ... + * + * */ +bool __nf_nat_mangle_tcp_packet(struct sk_buff *skb, + struct nf_conn *ct, + enum ip_conntrack_info ctinfo, + unsigned int protoff, + unsigned int match_offset, + unsigned int match_len, + const char *rep_buffer, + unsigned int rep_len, bool adjust) +{ + struct tcphdr *tcph; + int oldlen, datalen; + + if (skb_ensure_writable(skb, skb->len)) + return false; + + if (rep_len > match_len && + rep_len - match_len > skb_tailroom(skb) && + !enlarge_skb(skb, rep_len - match_len)) + return false; + + tcph = (void *)skb->data + protoff; + + oldlen = skb->len - protoff; + mangle_contents(skb, protoff + tcph->doff*4, + match_offset, match_len, rep_buffer, rep_len); + + datalen = skb->len - protoff; + + nf_nat_csum_recalc(skb, nf_ct_l3num(ct), IPPROTO_TCP, + tcph, &tcph->check, datalen, oldlen); + + if (adjust && rep_len != match_len) + nf_ct_seqadj_set(ct, ctinfo, tcph->seq, + (int)rep_len - (int)match_len); + + return true; +} +EXPORT_SYMBOL(__nf_nat_mangle_tcp_packet); + +/* Generic function for mangling variable-length address changes inside + * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX + * command in the Amanda protocol) + * + * Takes care about all the nasty sequence number changes, checksumming, + * skb enlargement, ... + * + * XXX - This function could be merged with nf_nat_mangle_tcp_packet which + * should be fairly easy to do. + */ +bool +nf_nat_mangle_udp_packet(struct sk_buff *skb, + struct nf_conn *ct, + enum ip_conntrack_info ctinfo, + unsigned int protoff, + unsigned int match_offset, + unsigned int match_len, + const char *rep_buffer, + unsigned int rep_len) +{ + struct udphdr *udph; + int datalen, oldlen; + + if (skb_ensure_writable(skb, skb->len)) + return false; + + if (rep_len > match_len && + rep_len - match_len > skb_tailroom(skb) && + !enlarge_skb(skb, rep_len - match_len)) + return false; + + udph = (void *)skb->data + protoff; + + oldlen = skb->len - protoff; + mangle_contents(skb, protoff + sizeof(*udph), + match_offset, match_len, rep_buffer, rep_len); + + /* update the length of the UDP packet */ + datalen = skb->len - protoff; + udph->len = htons(datalen); + + /* fix udp checksum if udp checksum was previously calculated */ + if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL) + return true; + + nf_nat_csum_recalc(skb, nf_ct_l3num(ct), IPPROTO_UDP, + udph, &udph->check, datalen, oldlen); + + return true; +} +EXPORT_SYMBOL(nf_nat_mangle_udp_packet); + +/* Setup NAT on this expected conntrack so it follows master. */ +/* If we fail to get a free NAT slot, we'll get dropped on confirm */ +void nf_nat_follow_master(struct nf_conn *ct, + struct nf_conntrack_expect *exp) +{ + struct nf_nat_range2 range; + + /* This must be a fresh one. */ + BUG_ON(ct->status & IPS_NAT_DONE_MASK); + + /* Change src to where master sends to */ + range.flags = NF_NAT_RANGE_MAP_IPS; + range.min_addr = range.max_addr + = ct->master->tuplehash[!exp->dir].tuple.dst.u3; + nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC); + + /* For DST manip, map port here to where it's expected. */ + range.flags = (NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED); + range.min_proto = range.max_proto = exp->saved_proto; + range.min_addr = range.max_addr + = ct->master->tuplehash[!exp->dir].tuple.src.u3; + nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST); +} +EXPORT_SYMBOL(nf_nat_follow_master); + +u16 nf_nat_exp_find_port(struct nf_conntrack_expect *exp, u16 port) +{ + static const unsigned int max_attempts = 128; + int range, attempts_left; + u16 min = port; + + range = USHRT_MAX - port; + attempts_left = range; + + if (attempts_left > max_attempts) + attempts_left = max_attempts; + + /* Try to get same port: if not, try to change it. */ + for (;;) { + int res; + + exp->tuple.dst.u.tcp.port = htons(port); + res = nf_ct_expect_related(exp, 0); + if (res == 0) + return port; + + if (res != -EBUSY || (--attempts_left < 0)) + break; + + port = min + prandom_u32_max(range); + } + + return 0; +} +EXPORT_SYMBOL_GPL(nf_nat_exp_find_port); |