// SPDX-License-Identifier: GPL-2.0-only
/* (C) 1999-2001 Paul `Rusty' Russell
* (C) 2002-2004 Netfilter Core Team <[email protected]>
*/
#include <linux/module.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/route.h>
#include <net/dst.h>
#include <net/netfilter/ipv4/nf_reject.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_bridge.h>
static int nf_reject_iphdr_validate(struct sk_buff *skb)
{
struct iphdr *iph;
u32 len;
if (!pskb_may_pull(skb, sizeof(struct iphdr)))
return 0;
iph = ip_hdr(skb);
if (iph->ihl < 5 || iph->version != 4)
return 0;
len = ntohs(iph->tot_len);
if (skb->len < len)
return 0;
else if (len < (iph->ihl*4))
return 0;
if (!pskb_may_pull(skb, iph->ihl*4))
return 0;
return 1;
}
struct sk_buff *nf_reject_skb_v4_tcp_reset(struct net *net,
struct sk_buff *oldskb,
const struct net_device *dev,
int hook)
{
const struct tcphdr *oth;
struct sk_buff *nskb;
struct iphdr *niph;
struct tcphdr _oth;
if (!nf_reject_iphdr_validate(oldskb))
return NULL;
oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
if (!oth)
return NULL;
nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
LL_MAX_HEADER, GFP_ATOMIC);
if (!nskb)
return NULL;
nskb->dev = (struct net_device *)dev;
skb_reserve(nskb, LL_MAX_HEADER);
niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
niph->tot_len = htons(nskb->len);
ip_send_check(niph);
return nskb;
}
EXPORT_SYMBOL_GPL(nf_reject_skb_v4_tcp_reset);
struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
struct sk_buff *oldskb,
const struct net_device *dev,
int hook, u8 code)
{
struct sk_buff *nskb;
struct iphdr *niph;
struct icmphdr *icmph;
unsigned int len;
int dataoff;
__wsum csum;
u8 proto;
if (!nf_reject_iphdr_validate(oldskb))
return NULL;
/* IP header checks: fragment. */
if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
return NULL;
/* RFC says return as much as we can without exceeding 576 bytes. */
len = min_t(unsigned int, 536, oldskb->len);
if (!pskb_may_pull(oldskb, len))
return NULL;
if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
return NULL;
dataoff = ip_hdrlen(oldskb);
proto = ip_hdr(oldskb)->protocol;
if (!skb_csum_unnecessary(oldskb) &&
nf_reject_verify_csum(oldskb, dataoff, proto) &&
nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
return NULL;
nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
LL_MAX_HEADER + len, GFP_ATOMIC);
if (!nskb)
return NULL;
nskb->dev = (struct net_device *)dev;
skb_reserve(nskb, LL_MAX_HEADER);
niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
skb_reset_transport_header(nskb);
icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
icmph->type = ICMP_DEST_UNREACH;
icmph->code = code;
skb_put_data(nskb, skb_network_header(oldskb), len);
csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
icmph->checksum = csum_fold(csum);
niph->tot_len = htons(nskb->len);
ip_send_check(niph);
return nskb;
}
EXPORT_SYMBOL_GPL(nf_reject_skb_v4_unreach);
const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
struct tcphdr *_oth, int hook)
{
const struct tcphdr *oth;
/* IP header checks: fragment. */
if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
return NULL;
if (ip_hdr(oldskb)->protocol != IPPROTO_TCP)
return NULL;
oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
sizeof(struct tcphdr), _oth);
if (oth == NULL)
return NULL;
/* No RST for RST. */
if (oth->rst)
return NULL;
/* Check checksum */
if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
return NULL;
return oth;
}
EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
const struct sk_buff *oldskb,
__u8 protocol, int ttl)
{
struct iphdr *niph, *oiph = ip_hdr(oldskb);
skb_reset_network_header(nskb);
niph = skb_put(nskb, sizeof(struct iphdr));
niph->version = 4;
niph->ihl = sizeof(struct iphdr) / 4;
niph->tos = 0;
niph->id = 0;
niph->frag_off = htons(IP_DF);
niph->protocol = protocol;
niph->check = 0;
niph->saddr = oiph->daddr;
niph->daddr = oiph->saddr;
niph->ttl = ttl;
nskb->protocol = htons(ETH_P_IP);
return niph;
}
EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
const struct tcphdr *oth)
{
struct iphdr *niph = ip_hdr(nskb);
struct tcphdr *tcph;
skb_reset_transport_header(nskb);
tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
tcph->source = oth->dest;
tcph->dest = oth->source;
tcph->doff = sizeof(struct tcphdr) / 4;
if (oth->ack) {
tcph->seq = oth->ack_seq;
} else {
tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
oldskb->len - ip_hdrlen(oldskb) -
(oth->doff << 2));
tcph->ack = 1;
}
tcph->rst = 1;
tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
niph->daddr, 0);
nskb->ip_summed = CHECKSUM_PARTIAL;
nskb->csum_start = (unsigned char *)tcph - nskb->head;
nskb->csum_offset = offsetof(struct tcphdr, check);
}
EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
{
struct dst_entry *dst = NULL;
struct flowi fl;
memset(&fl, 0, sizeof(struct flowi));
fl.u.ip4.daddr = ip_hdr(skb_in)->saddr;
nf_ip_route(dev_net(skb_in->dev), &dst, &fl, false);
if (!dst)
return -1;
skb_dst_set(skb_in, dst);
return 0;
}
/* Send RST reply */
void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
int hook)
{
const struct tcphdr *oth;
struct sk_buff *nskb;
struct tcphdr _oth;
oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
if (!oth)
return;
if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
nf_reject_fill_skb_dst(oldskb) < 0)
return;
if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
return;
nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
LL_MAX_HEADER, GFP_ATOMIC);
if (!nskb)
return;
/* ip_route_me_harder expects skb->dst to be set */
skb_dst_set_noref(nskb, skb_dst(oldskb));
nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
skb_reserve(nskb, LL_MAX_HEADER);
nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
ip4_dst_hoplimit(skb_dst(nskb)));
nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
if (ip_route_me_harder(net, sk, nskb, RTN_UNSPEC))
goto free_nskb;
/* "Never happens" */
if (nskb->len > dst_mtu(skb_dst(nskb)))
goto free_nskb;
nf_ct_attach(nskb, oldskb);
nf_ct_set_closing(skb_nfct(oldskb));
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
/* If we use ip_local_out for bridged traffic, the MAC source on
* the RST will be ours, instead of the destination's. This confuses
* some routers/firewalls, and they drop the packet. So we need to
* build the eth header using the original destination's MAC as the
* source, and send the RST packet directly.
*/
if (nf_bridge_info_exists(oldskb)) {
struct ethhdr *oeth = eth_hdr(oldskb);
struct iphdr *niph = ip_hdr(nskb);
struct net_device *br_indev;
br_indev = nf_bridge_get_physindev(oldskb, net);
if (!br_indev)
goto free_nskb;
nskb->dev = br_indev;
niph->tot_len = htons(nskb->len);
ip_send_check(niph);
if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
oeth->h_source, oeth->h_dest, nskb->len) < 0)
goto free_nskb;
dev_queue_xmit(nskb);
} else
#endif
ip_local_out(net, nskb->sk, nskb);
return;
free_nskb:
kfree_skb(nskb);
}
EXPORT_SYMBOL_GPL(nf_send_reset);
void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
{
struct iphdr *iph = ip_hdr(skb_in);
int dataoff = ip_hdrlen(skb_in);
u8 proto = iph->protocol;
if (iph->frag_off & htons(IP_OFFSET))
return;
if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
nf_reject_fill_skb_dst(skb_in) < 0)
return;
if (skb_csum_unnecessary(skb_in) ||
!nf_reject_verify_csum(skb_in, dataoff, proto)) {
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
return;
}
if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
}
EXPORT_SYMBOL_GPL(nf_send_unreach);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("IPv4 packet rejection core");
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