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[NETFILTER]: ipt_REJECT: properly handle IP options

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The current TCP RST construction reuses the old packet and can't
deal with IP options as a consequence of that. Construct the
RST from scratch instead.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Denys Vlasenko 2008-01-14 23:44:26 -08:00 committed by David S. Miller
parent 022748a935
commit 9ba99b0d3f
1 changed files with 34 additions and 62 deletions
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96
net/ipv4/netfilter/ipt_REJECT.c
View File

@ -35,11 +35,8 @@ MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv4");
static void send_reset(struct sk_buff *oldskb, int hook)
{
struct sk_buff *nskb;
struct iphdr *niph;
struct iphdr *oiph, *niph;
struct tcphdr _otcph, *oth, *tcph;
__be16 tmp_port;
__be32 tmp_addr;
int needs_ack;
unsigned int addr_type;
/* IP header checks: fragment. */
@ -58,69 +55,47 @@ static void send_reset(struct sk_buff *oldskb, int hook)
/* Check checksum */
if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
return;
oiph = ip_hdr(oldskb);
/* We need a linear, writeable skb. We also need to expand
headroom in case hh_len of incoming interface < hh_len of
outgoing interface */
nskb = skb_copy_expand(oldskb, LL_MAX_HEADER, skb_tailroom(oldskb),
GFP_ATOMIC);
nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
LL_MAX_HEADER, GFP_ATOMIC);
if (!nskb)
return;
/* This packet will not be the same as the other: clear nf fields */
nf_reset(nskb);
nskb->mark = 0;
skb_init_secmark(nskb);
skb_reserve(nskb, LL_MAX_HEADER);
skb_shinfo(nskb)->gso_size = 0;
skb_shinfo(nskb)->gso_segs = 0;
skb_shinfo(nskb)->gso_type = 0;
skb_reset_network_header(nskb);
niph = (struct iphdr *)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 = IPPROTO_TCP;
niph->check = 0;
niph->saddr = oiph->daddr;
niph->daddr = oiph->saddr;
tcph = (struct tcphdr *)(skb_network_header(nskb) + ip_hdrlen(nskb));
tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
memset(tcph, 0, sizeof(*tcph));
tcph->source = oth->dest;
tcph->dest = oth->source;
tcph->doff = sizeof(struct tcphdr) / 4;
/* Swap source and dest */
niph = ip_hdr(nskb);
tmp_addr = niph->saddr;
niph->saddr = niph->daddr;
niph->daddr = tmp_addr;
tmp_port = tcph->source;
tcph->source = tcph->dest;
tcph->dest = tmp_port;
/* Truncate to length (no data) */
tcph->doff = sizeof(struct tcphdr)/4;
skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr));
if (tcph->ack) {
needs_ack = 0;
if (oth->ack)
tcph->seq = oth->ack_seq;
tcph->ack_seq = 0;
} else {
needs_ack = 1;
else {
tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
oldskb->len - ip_hdrlen(oldskb) -
(oth->doff << 2));
tcph->seq = 0;
tcph->ack = 1;
}
/* Reset flags */
((u_int8_t *)tcph)[13] = 0;
tcph->rst = 1;
tcph->ack = needs_ack;
tcph->window = 0;
tcph->urg_ptr = 0;
/* Adjust TCP checksum */
tcph->check = 0;
tcph->check = tcp_v4_check(sizeof(struct tcphdr),
niph->saddr, niph->daddr,
csum_partial(tcph,
sizeof(struct tcphdr), 0));
/* Set DF, id = 0 */
niph->frag_off = htons(IP_DF);
niph->id = 0;
tcph->rst = 1;
tcph->check = tcp_v4_check(sizeof(struct tcphdr),
niph->saddr, niph->daddr,
csum_partial(tcph,
sizeof(struct tcphdr), 0));
addr_type = RTN_UNSPEC;
if (hook != NF_INET_FORWARD
@ -130,14 +105,16 @@ static void send_reset(struct sk_buff *oldskb, int hook)
)
addr_type = RTN_LOCAL;
/* ip_route_me_harder expects skb->dst to be set */
dst_hold(oldskb->dst);
nskb->dst = oldskb->dst;
if (ip_route_me_harder(nskb, addr_type))
goto free_nskb;
niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
nskb->ip_summed = CHECKSUM_NONE;
/* Adjust IP TTL */
niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);
/* "Never happens" */
if (nskb->len > dst_mtu(nskb->dst))
goto free_nskb;
@ -163,11 +140,6 @@ reject_tg(struct sk_buff *skb, const struct net_device *in,
{
const struct ipt_reject_info *reject = targinfo;
/* Our naive response construction doesn't deal with IP
options, and probably shouldn't try. */
if (ip_hdrlen(skb) != sizeof(struct iphdr))
return NF_DROP;
/* WARNING: This code causes reentry within iptables.
This means that the iptables jump stack is now crap. We
must return an absolute verdict. --RR */