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/**************************************************************************
*
* Copyright (c) 2013 Alcatel-Lucent
*
* Alcatel Lucent licenses this file to You under the Apache License,
* Version 2.0 (the "License"); you may not use this file except in
* compliance with the License. A copy of the License is contained the
* file LICENSE at the top level of this repository.
* You may also obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
**************************************************************************
*
* tcpstuff.c
*
* Absolute minimum to properly refuse TCP connection requests to this
* device. The processTCP function is called if the incoming protocol is
* TCP, but this code simply responds with a TCP RESET which is essentially
* a refusal to establish the connection request being made from a remote
* machine.
* This is similar in functionality to the ICMP "destination unreachable
* message". Note that this is not an absolute necessity but it does
* provide a "clean" response to the remote machine that is making the
* connection request. Without it, the remote machine would keep trying
* to connect.
* For more details, refer to TCP/IP Comer 3rd Edition pg 216-219.
*
* Original author: Ed Sutter (ed.sutter@alcatel-lucent.com)
*
*/
#include "config.h"
#include "endian.h"
#if INCLUDE_ETHERNET
#include "genlib.h"
#include "ether.h"
#include "stddefs.h"
/* SendTcpConnectionReset():
* Called in response to any incoming TCP request.
* It is used to let the sender know that the TCP connection is being
* refused.
*/
int
SendTcpConnectionReset(struct ether_header *re)
{
short datalen, flags;
ulong ackno;
struct ether_header *te;
struct ip *ti, *ri;
struct tcphdr *ttcp, *rtcp;
ri = (struct ip *) (re + 1);
datalen = ecs(ri->ip_len) - ((ri->ip_vhl & 0x0f) * 4);
te = EtherCopy(re);
ti = (struct ip *) (te + 1);
ti->ip_vhl = ri->ip_vhl;
ti->ip_tos = ri->ip_tos;
ti->ip_len = ri->ip_len;
ti->ip_id = ri->ip_id;
ti->ip_off = ecs(IP_DONTFRAG);
ti->ip_ttl = ri->ip_ttl/2;
ti->ip_p = ri->ip_p;
memcpy((char *)&(ti->ip_src.s_addr),(char *)&(ri->ip_dst.s_addr),
sizeof(struct in_addr));
memcpy((char *)&(ti->ip_dst.s_addr),(char *)&(ri->ip_src.s_addr),
sizeof(struct in_addr));
ttcp = (struct tcphdr *) (ti + 1);
rtcp = (struct tcphdr *) (ri + 1);
flags = ecs(rtcp->flags);
flags &= ~TCP_FLAGMASK;
flags |= (TCP_ACK | TCP_RESET);
ttcp->flags = ecs(flags);
ttcp->sport = rtcp->dport;
ttcp->dport = rtcp->sport;
memset((char *)&ttcp->seqno,0,4);
memcpy((char *)&ackno,(char *)&rtcp->seqno,4);
self_ecl(ackno);
ackno+=1;
self_ecl(ackno);
memcpy((char *)&ttcp->ackno,(char *)&ackno,4);
ttcp->windowsize = 0;
ttcp->urgentptr = 0;
memcpy((char *)(ttcp+1),(char *)(rtcp+1),datalen-sizeof(struct tcphdr));
ipChksum(ti); /* compute checksum of ip hdr: (3rd Edition Comer pg 100) */
tcpChksum(ti); /* Compute TCP checksum */
sendBuffer(sizeof(struct ether_header) + ecs(ti->ip_len));
return(0);
}
/* tcpChksum():
* Compute the checksum of the TCP packet.
* The incoming pointer is to an ip header, the tcp header after that ip
* header is directly populated with the result. Similar to the udp
* checksum calculation. This one is mandatory.
*/
void
tcpChksum(struct ip *ihdr)
{
register int i;
register ushort *sp;
register ulong t;
short len;
struct tcphdr *thdr;
struct UdpPseudohdr pseudohdr;
thdr = (struct tcphdr *)(ihdr+1);
thdr->tcpcsum = 0;
/* Start by building the pseudo header: */
memcpy((char *)&pseudohdr.ip_src.s_addr,(char *)&ihdr->ip_src.s_addr,4);
memcpy((char *)&pseudohdr.ip_dst.s_addr,(char *)&ihdr->ip_dst.s_addr,4);
pseudohdr.zero = 0;
pseudohdr.proto = ihdr->ip_p;
len = ecs(ihdr->ip_len) - sizeof(struct ip);
pseudohdr.ulen = ecs(len);
/* Get checksum of pseudo header: */
sp = (ushort *) &pseudohdr;
for (i=0,t=0;i<(sizeof(struct UdpPseudohdr)/sizeof(ushort));i++,sp++)
t += *sp;
/* If length is odd, pad and add one. */
if (len & 1) {
uchar *ucp;
ucp = (uchar *)thdr;
ucp[len] = 0;
len++;
}
len >>= 1;
sp = (ushort *) thdr;
for (i=0;i<len;i++,sp++)
t += *sp;
t = (t & 0xffff) + (t >> 16);
thdr->tcpcsum = ~t;
}
void
tcperrmsg(char *msg)
{
printf("TCP error: %s\n",msg);
}
void
processTCP(struct ether_header *ehdr,ushort size)
{
//struct ip *ipp;
//struct tcphdr *tcpp;
//ipp = (struct ip *)(ehdr + 1);
//tcpp = (struct tcphdr *)((char *)ipp + IP_HLEN(ipp));
SendTcpConnectionReset(ehdr);
return;
}
#endif
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