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#include <linux/module.h>
#include <net/ip.h>
#include <linux/ipv6.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_tcpudp.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
MODULE_DESCRIPTION("x_tables match for TCP and UDP, supports IPv4 and IPv6");
MODULE_LICENSE("GPL");
MODULE_ALIAS("xt_tcp");
MODULE_ALIAS("xt_udp");
MODULE_ALIAS("ipt_udp");
MODULE_ALIAS("ipt_tcp");
MODULE_ALIAS("ip6t_udp");
MODULE_ALIAS("ip6t_tcp");
#ifdef DEBUG_IP_FIREWALL_USER
#define duprintf(format, args...) printk(format , ## args)
#else
#define duprintf(format, args...)
#endif
/* Returns 1 if the port is matched by the range, 0 otherwise */
static inline int
port_match(u_int16_t min, u_int16_t max, u_int16_t port, int invert)
{
int ret;
ret = (port >= min && port <= max) ^ invert;
return ret;
}
static int
tcp_find_option(u_int8_t option,
const struct sk_buff *skb,
unsigned int protoff,
unsigned int optlen,
int invert,
int *hotdrop)
{
/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
u_int8_t _opt[60 - sizeof(struct tcphdr)], *op;
unsigned int i;
duprintf("tcp_match: finding option\n");
if (!optlen)
return invert;
/* If we don't have the whole header, drop packet. */
op = skb_header_pointer(skb, protoff + sizeof(struct tcphdr),
optlen, _opt);
if (op == NULL) {
*hotdrop = 1;
return 0;
}
for (i = 0; i < optlen; ) {
if (op[i] == option) return !invert;
if (op[i] < 2) i++;
else i += op[i+1]?:1;
}
return invert;
}
static int
tcp_match(const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
const struct xt_match *match,
const void *matchinfo,
int offset,
unsigned int protoff,
int *hotdrop)
{
struct tcphdr _tcph, *th;
const struct xt_tcp *tcpinfo = matchinfo;
if (offset) {
/* To quote Alan:
Don't allow a fragment of TCP 8 bytes in. Nobody normal
causes this. Its a cracker trying to break in by doing a
flag overwrite to pass the direction checks.
*/
if (offset == 1) {
duprintf("Dropping evil TCP offset=1 frag.\n");
*hotdrop = 1;
}
/* Must not be a fragment. */
return 0;
}
#define FWINVTCP(bool,invflg) ((bool) ^ !!(tcpinfo->invflags & invflg))
th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
if (th == NULL) {
/* We've been asked to examine this packet, and we
can't. Hence, no choice but to drop. */
duprintf("Dropping evil TCP offset=0 tinygram.\n");
*hotdrop = 1;
return 0;
}
if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
ntohs(th->source),
!!(tcpinfo->invflags & XT_TCP_INV_SRCPT)))
return 0;
if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
ntohs(th->dest),
!!(tcpinfo->invflags & XT_TCP_INV_DSTPT)))
return 0;
if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
== tcpinfo->flg_cmp,
XT_TCP_INV_FLAGS))
return 0;
if (tcpinfo->option) {
if (th->doff * 4 < sizeof(_tcph)) {
*hotdrop = 1;
return 0;
}
if (!tcp_find_option(tcpinfo->option, skb, protoff,
th->doff*4 - sizeof(_tcph),
tcpinfo->invflags & XT_TCP_INV_OPTION,
hotdrop))
return 0;
}
return 1;
}
/* Called when user tries to insert an entry of this type. */
static int
tcp_checkentry(const char *tablename,
const void *info,
const struct xt_match *match,
void *matchinfo,
unsigned int matchsize,
unsigned int hook_mask)
{
const struct xt_tcp *tcpinfo = matchinfo;
/* Must specify no unknown invflags */
return !(tcpinfo->invflags & ~XT_TCP_INV_MASK);
}
static int
udp_match(const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
const struct xt_match *match,
const void *matchinfo,
int offset,
unsigned int protoff,
int *hotdrop)
{
struct udphdr _udph, *uh;
const struct xt_udp *udpinfo = matchinfo;
/* Must not be a fragment. */
if (offset)
return 0;
uh = skb_header_pointer(skb, protoff, sizeof(_udph), &_udph);
if (uh == NULL) {
/* We've been asked to examine this packet, and we
can't. Hence, no choice but to drop. */
duprintf("Dropping evil UDP tinygram.\n");
*hotdrop = 1;
return 0;
}
return port_match(udpinfo->spts[0], udpinfo->spts[1],
ntohs(uh->source),
!!(udpinfo->invflags & XT_UDP_INV_SRCPT))
&& port_match(udpinfo->dpts[0], udpinfo->dpts[1],
ntohs(uh->dest),
!!(udpinfo->invflags & XT_UDP_INV_DSTPT));
}
/* Called when user tries to insert an entry of this type. */
static int
udp_checkentry(const char *tablename,
const void *info,
const struct xt_match *match,
void *matchinfo,
unsigned int matchsize,
unsigned int hook_mask)
{
const struct xt_tcp *udpinfo = matchinfo;
/* Must specify no unknown invflags */
return !(udpinfo->invflags & ~XT_UDP_INV_MASK);
}
static struct xt_match tcp_matchstruct = {
.name = "tcp",
.match = tcp_match,
.matchsize = sizeof(struct xt_tcp),
.proto = IPPROTO_TCP,
.family = AF_INET,
.checkentry = tcp_checkentry,
.me = THIS_MODULE,
};
static struct xt_match tcp6_matchstruct = {
.name = "tcp",
.match = tcp_match,
.matchsize = sizeof(struct xt_tcp),
.proto = IPPROTO_TCP,
.family = AF_INET6,
.checkentry = tcp_checkentry,
.me = THIS_MODULE,
};
static struct xt_match udp_matchstruct = {
.name = "udp",
.match = udp_match,
.matchsize = sizeof(struct xt_udp),
.proto = IPPROTO_UDP,
.family = AF_INET,
.checkentry = udp_checkentry,
.me = THIS_MODULE,
};
static struct xt_match udp6_matchstruct = {
.name = "udp",
.match = udp_match,
.matchsize = sizeof(struct xt_udp),
.proto = IPPROTO_UDP,
.family = AF_INET6,
.checkentry = udp_checkentry,
.me = THIS_MODULE,
};
static int __init xt_tcpudp_init(void)
{
int ret;
ret = xt_register_match(&tcp_matchstruct);
if (ret)
return ret;
ret = xt_register_match(&tcp6_matchstruct);
if (ret)
goto out_unreg_tcp;
ret = xt_register_match(&udp_matchstruct);
if (ret)
goto out_unreg_tcp6;
ret = xt_register_match(&udp6_matchstruct);
if (ret)
goto out_unreg_udp;
return ret;
out_unreg_udp:
xt_unregister_match(&udp_matchstruct);
out_unreg_tcp6:
xt_unregister_match(&tcp6_matchstruct);
out_unreg_tcp:
xt_unregister_match(&tcp_matchstruct);
return ret;
}
static void __exit xt_tcpudp_fini(void)
{
xt_unregister_match(&udp6_matchstruct);
xt_unregister_match(&udp_matchstruct);
xt_unregister_match(&tcp6_matchstruct);
xt_unregister_match(&tcp_matchstruct);
}
module_init(xt_tcpudp_init);
module_exit(xt_tcpudp_fini);
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