diff options
Diffstat (limited to 'sys/netinet/libalias/alias_ftp.c')
| -rw-r--r-- | sys/netinet/libalias/alias_ftp.c | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/sys/netinet/libalias/alias_ftp.c b/sys/netinet/libalias/alias_ftp.c new file mode 100644 index 0000000..ca2d53b --- /dev/null +++ b/sys/netinet/libalias/alias_ftp.c @@ -0,0 +1,231 @@ +/* + Alias_ftp.c performs special processing for FTP sessions under + TCP. Specifically, when a PORT command from the client side + is sent, it is intercepted and modified. The address is changed + to the gateway machine and an aliasing port is used. + + For this routine to work, the PORT command must fit entirely + into a single TCP packet. This is typically the case, but exceptions + can easily be envisioned under the actual specifications. + + Probably the most troubling aspect of the approach taken here is + that the new PORT command will typically be a different length, and + this causes a certain amount of bookkeeping to keep track of the + changes of sequence and acknowledgment numbers, since the client + machine is totally unaware of the modification to the TCP stream. + + + This software is placed into the public domain with no restrictions + on its distribution. + + Initial version: August, 1996 (cjm) + + Version 1.6 + Brian Somers and Martin Renters identified an IP checksum + error for modified IP packets. + + Version 1.7: January 9, 1996 (cjm) + Differental checksum computation for change + in IP packet length. + + Version 2.1: May, 1997 (cjm) + Very minor changes to conform with + local/global/function naming conventions + withing the packet alising module. + + See HISTORY file for record of revisions. + + $FreeBSD$ +*/ + +/* Includes */ +#include <ctype.h> +#include <stdio.h> +#include <string.h> +#include <sys/types.h> +#include <netinet/in_systm.h> +#include <netinet/in.h> +#include <netinet/ip.h> +#include <netinet/tcp.h> + +#include "alias_local.h" + +static void NewFtpPortCommand(struct ip *, struct alias_link *, struct in_addr, u_short, int); + + + +void +AliasHandleFtpOut( +struct ip *pip, /* IP packet to examine/patch */ +struct alias_link *link, /* The link to go through (aliased port) */ +int maxpacketsize /* The maximum size this packet can grow to (including headers) */) +{ + int hlen, tlen, dlen; + struct in_addr true_addr; + u_short true_port; + char *sptr; + struct tcphdr *tc; + +/* Calculate data length of TCP packet */ + tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); + hlen = (pip->ip_hl + tc->th_off) << 2; + tlen = ntohs(pip->ip_len); + dlen = tlen - hlen; + +/* Return is data length is too long or too short */ + if (dlen<10 || dlen>80) + return; + +/* Place string pointer and beginning of data */ + sptr = (char *) pip; + sptr += hlen; + +/* Parse through string using state diagram method */ + { + char ch, zero; + int i, state; + u_long a1, a2, a3, a4; + u_short p1, p2; + + a1=0; a2=0; a3=0; a4=0; p1=0; p2=0; + zero = '0'; + state=-4; + for (i=0; i<dlen; i++) + { + ch = sptr[i]; + switch (state) + { + case -4: if (ch == 'P') state=-3; else return; break; + case -3: if (ch == 'O') state=-2; else return; break; + case -2: if (ch == 'R') state=-1; else return; break; + case -1: if (ch == 'T') state= 0; else return; break; + + case 0 : + if (isdigit(ch)) {a1=ch-zero; state=1 ;} break; + case 1 : + if (isdigit(ch)) a1=10*a1+ch-zero; else state=2 ; break; + case 2 : + if (isdigit(ch)) {a2=ch-zero; state=3 ;} break; + case 3 : + if (isdigit(ch)) a2=10*a2+ch-zero; else state=4 ; break; + case 4 : + if (isdigit(ch)) {a3=ch-zero; state=5 ;} break; + case 5 : + if (isdigit(ch)) a3=10*a3+ch-zero; else state=6 ; break; + case 6 : + if (isdigit(ch)) {a4=ch-zero; state=7 ;} break; + case 7 : + if (isdigit(ch)) a4=10*a4+ch-zero; else state=8 ; break; + case 8 : + if (isdigit(ch)) {p1=ch-zero; state=9 ;} break; + case 9 : + if (isdigit(ch)) p1=10*p1+ch-zero; else state=10; break; + case 10: + if (isdigit(ch)) {p2=ch-zero; state=11;} break; + case 11: + if (isdigit(ch)) p2=10*p2+ch-zero; break; + } + } + + if (state == 11) + { + true_port = htons((p1<<8) + p2); + true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4); + NewFtpPortCommand(pip, link, true_addr, true_port, maxpacketsize); + } + } +} + +static void +NewFtpPortCommand(struct ip *pip, + struct alias_link *link, + struct in_addr true_addr, + u_short true_port, + int maxpacketsize) +{ + struct alias_link *ftp_link; + +/* Establish link to address and port found in PORT command */ + ftp_link = FindUdpTcpOut(true_addr, GetDestAddress(link), + true_port, 0, IPPROTO_TCP); + + if (ftp_link != NULL) + { + int slen, hlen, tlen, dlen; + struct tcphdr *tc; + +#ifndef NO_FW_PUNCH +/* Punch hole in firewall */ + PunchFWHole(ftp_link); +#endif + +/* Calculate data length of TCP packet */ + tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); + hlen = (pip->ip_hl + tc->th_off) << 2; + tlen = ntohs(pip->ip_len); + dlen = tlen - hlen; + +/* Create new PORT command */ + { + char stemp[80]; + char *sptr; + u_short alias_port; + u_char *ptr; + int a1, a2, a3, a4, p1, p2; + struct in_addr alias_address; + +/* Decompose alias address into quad format */ + alias_address = GetAliasAddress(link); + ptr = (u_char *) &alias_address.s_addr; + a1 = *ptr++; a2=*ptr++; a3=*ptr++; a4=*ptr; + +/* Decompose alias port into pair format */ + alias_port = GetAliasPort(ftp_link); + ptr = (char *) &alias_port; + p1 = *ptr++; p2=*ptr; + +/* Generate command string */ + sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n", + a1,a2,a3,a4,p1,p2); + +/* Save string length for IP header modification */ + slen = strlen(stemp); + +/* Copy into IP packet */ + sptr = (char *) pip; sptr += hlen; + strncpy(sptr, stemp, maxpacketsize-hlen); + } + +/* Save information regarding modified seq and ack numbers */ + { + int delta; + + SetAckModified(link); + delta = GetDeltaSeqOut(pip, link); + AddSeq(pip, link, delta+slen-dlen); + } + +/* Revise IP header */ + { + u_short new_len; + + new_len = htons(hlen + slen); + DifferentialChecksum(&pip->ip_sum, + &new_len, + &pip->ip_len, + 1); + pip->ip_len = new_len; + } + +/* Compute TCP checksum for revised packet */ + tc->th_sum = 0; + tc->th_sum = TcpChecksum(pip); + } + else + { +#ifdef DEBUG + fprintf(stderr, + "PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n"); +#endif + } +} |
