diff options
Diffstat (limited to 'lib/libalias/alias_pptp.c')
| -rw-r--r-- | lib/libalias/alias_pptp.c | 369 |
1 files changed, 369 insertions, 0 deletions
diff --git a/lib/libalias/alias_pptp.c b/lib/libalias/alias_pptp.c new file mode 100644 index 0000000..2d3d9ac --- /dev/null +++ b/lib/libalias/alias_pptp.c @@ -0,0 +1,369 @@ +/* + * alias_pptp.c + * + * Copyright (c) 2000 Whistle Communications, Inc. + * All rights reserved. + * + * Subject to the following obligations and disclaimer of warranty, use and + * redistribution of this software, in source or object code forms, with or + * without modifications are expressly permitted by Whistle Communications; + * provided, however, that: + * 1. Any and all reproductions of the source or object code must include the + * copyright notice above and the following disclaimer of warranties; and + * 2. No rights are granted, in any manner or form, to use Whistle + * Communications, Inc. trademarks, including the mark "WHISTLE + * COMMUNICATIONS" on advertising, endorsements, or otherwise except as + * such appears in the above copyright notice or in the software. + * + * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND + * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO + * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE, + * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. + * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY + * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS + * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE. + * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES + * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING + * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, + * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR + * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF + * THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY + * OF SUCH DAMAGE. + * + * Author: Erik Salander <erik@whistle.com> + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +/* + Alias_pptp.c performs special processing for PPTP sessions under TCP. + Specifically, watch PPTP control messages and alias the Call ID or the + Peer's Call ID in the appropriate messages. Note, PPTP requires + "de-aliasing" of incoming packets, this is different than any other + TCP applications that are currently (ie. FTP, IRC and RTSP) aliased. + + For Call IDs encountered for the first time, a PPTP alias link is created. + The PPTP alias link uses the Call ID in place of the original port number. + An alias Call ID is created. + + For this routine to work, the PPTP control messages must fit entirely + into a single TCP packet. This is typically the case, but is not + required by the spec. + + Unlike some of the other TCP applications that are aliased (ie. FTP, + IRC and RTSP), the PPTP control messages that need to be aliased are + guaranteed to remain the same length. The aliased Call ID is a fixed + length field. + + Reference: RFC 2637 + + Initial version: May, 2000 (eds) + +*/ + +/* Includes */ +#include <sys/types.h> +#include <netinet/in_systm.h> +#include <netinet/in.h> +#include <netinet/ip.h> +#include <netinet/tcp.h> + +#include <stdio.h> + +#include "alias_local.h" + +/* + * PPTP definitions + */ + +struct grehdr /* Enhanced GRE header. */ +{ + u_int16_t gh_flags; /* Flags. */ + u_int16_t gh_protocol; /* Protocol type. */ + u_int16_t gh_length; /* Payload length. */ + u_int16_t gh_call_id; /* Call ID. */ + u_int32_t gh_seq_no; /* Sequence number (optional). */ + u_int32_t gh_ack_no; /* Acknowledgment number (optional). */ +}; +typedef struct grehdr GreHdr; + +/* The PPTP protocol ID used in the GRE 'proto' field. */ +#define PPTP_GRE_PROTO 0x880b + +/* Bits that must be set a certain way in all PPTP/GRE packets. */ +#define PPTP_INIT_VALUE ((0x2001 << 16) | PPTP_GRE_PROTO) +#define PPTP_INIT_MASK 0xef7fffff + +#define PPTP_MAGIC 0x1a2b3c4d +#define PPTP_CTRL_MSG_TYPE 1 + +enum { + PPTP_StartCtrlConnRequest = 1, + PPTP_StartCtrlConnReply = 2, + PPTP_StopCtrlConnRequest = 3, + PPTP_StopCtrlConnReply = 4, + PPTP_EchoRequest = 5, + PPTP_EchoReply = 6, + PPTP_OutCallRequest = 7, + PPTP_OutCallReply = 8, + PPTP_InCallRequest = 9, + PPTP_InCallReply = 10, + PPTP_InCallConn = 11, + PPTP_CallClearRequest = 12, + PPTP_CallDiscNotify = 13, + PPTP_WanErrorNotify = 14, + PPTP_SetLinkInfo = 15 +}; + + /* Message structures */ + struct pptpMsgHead { + u_int16_t length; /* total length */ + u_int16_t msgType; /* PPTP message type */ + u_int32_t magic; /* magic cookie */ + u_int16_t type; /* control message type */ + u_int16_t resv0; /* reserved */ + }; + typedef struct pptpMsgHead *PptpMsgHead; + + struct pptpCodes { + u_int8_t resCode; /* Result Code */ + u_int8_t errCode; /* Error Code */ + }; + typedef struct pptpCodes *PptpCode; + + struct pptpCallIds { + u_int16_t cid1; /* Call ID field #1 */ + u_int16_t cid2; /* Call ID field #2 */ + }; + typedef struct pptpCallIds *PptpCallId; + +static PptpCallId AliasVerifyPptp(struct ip *, u_int16_t *); + + +void +AliasHandlePptpOut(struct ip *pip, /* IP packet to examine/patch */ + struct alias_link *link) /* The PPTP control link */ +{ + struct alias_link *pptp_link; + PptpCallId cptr; + PptpCode codes; + u_int16_t ctl_type; /* control message type */ + struct tcphdr *tc; + + /* Verify valid PPTP control message */ + if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL) + return; + + /* Modify certain PPTP messages */ + switch (ctl_type) { + case PPTP_OutCallRequest: + case PPTP_OutCallReply: + case PPTP_InCallRequest: + case PPTP_InCallReply: + /* Establish PPTP link for address and Call ID found in control message. */ + pptp_link = AddPptp(GetOriginalAddress(link), GetDestAddress(link), + GetAliasAddress(link), cptr->cid1); + break; + case PPTP_CallClearRequest: + case PPTP_CallDiscNotify: + /* Find PPTP link for address and Call ID found in control message. */ + pptp_link = FindPptpOutByCallId(GetOriginalAddress(link), + GetDestAddress(link), + cptr->cid1); + break; + default: + return; + } + + if (pptp_link != NULL) { + int accumulate = cptr->cid1; + + /* alias the Call Id */ + cptr->cid1 = GetAliasPort(pptp_link); + + /* Compute TCP checksum for revised packet */ + tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); + accumulate -= cptr->cid1; + ADJUST_CHECKSUM(accumulate, tc->th_sum); + + switch (ctl_type) { + case PPTP_OutCallReply: + case PPTP_InCallReply: + codes = (PptpCode)(cptr + 1); + if (codes->resCode == 1) /* Connection established, */ + SetDestCallId(pptp_link, /* note the Peer's Call ID. */ + cptr->cid2); + else + SetExpire(pptp_link, 0); /* Connection refused. */ + break; + case PPTP_CallDiscNotify: /* Connection closed. */ + SetExpire(pptp_link, 0); + break; + } + } +} + +void +AliasHandlePptpIn(struct ip *pip, /* IP packet to examine/patch */ + struct alias_link *link) /* The PPTP control link */ +{ + struct alias_link *pptp_link; + PptpCallId cptr; + u_int16_t *pcall_id; + u_int16_t ctl_type; /* control message type */ + struct tcphdr *tc; + + /* Verify valid PPTP control message */ + if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL) + return; + + /* Modify certain PPTP messages */ + switch (ctl_type) + { + case PPTP_InCallConn: + case PPTP_WanErrorNotify: + case PPTP_SetLinkInfo: + pcall_id = &cptr->cid1; + break; + case PPTP_OutCallReply: + case PPTP_InCallReply: + pcall_id = &cptr->cid2; + break; + case PPTP_CallDiscNotify: /* Connection closed. */ + pptp_link = FindPptpInByCallId(GetDestAddress(link), + GetAliasAddress(link), + cptr->cid1); + if (pptp_link != NULL) + SetExpire(pptp_link, 0); + return; + default: + return; + } + + /* Find PPTP link for address and Call ID found in PPTP Control Msg */ + pptp_link = FindPptpInByPeerCallId(GetDestAddress(link), + GetAliasAddress(link), + *pcall_id); + + if (pptp_link != NULL) { + int accumulate = *pcall_id; + + /* De-alias the Peer's Call Id. */ + *pcall_id = GetOriginalPort(pptp_link); + + /* Compute TCP checksum for modified packet */ + tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); + accumulate -= *pcall_id; + ADJUST_CHECKSUM(accumulate, tc->th_sum); + + if (ctl_type == PPTP_OutCallReply || ctl_type == PPTP_InCallReply) { + PptpCode codes = (PptpCode)(cptr + 1); + + if (codes->resCode == 1) /* Connection established, */ + SetDestCallId(pptp_link, /* note the Call ID. */ + cptr->cid1); + else + SetExpire(pptp_link, 0); /* Connection refused. */ + } + } +} + +static PptpCallId +AliasVerifyPptp(struct ip *pip, u_int16_t *ptype) /* IP packet to examine/patch */ +{ + int hlen, tlen, dlen; + PptpMsgHead hptr; + struct tcphdr *tc; + + /* Calculate some lengths */ + 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; + + /* Verify data length */ + if (dlen < (sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds))) + return(NULL); + + /* Move up to PPTP message header */ + hptr = (PptpMsgHead)(((char *) pip) + hlen); + + /* Return the control message type */ + *ptype = ntohs(hptr->type); + + /* Verify PPTP Control Message */ + if ((ntohs(hptr->msgType) != PPTP_CTRL_MSG_TYPE) || + (ntohl(hptr->magic) != PPTP_MAGIC)) + return(NULL); + + /* Verify data length. */ + if ((*ptype == PPTP_OutCallReply || *ptype == PPTP_InCallReply) && + (dlen < sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds) + + sizeof(struct pptpCodes))) + return (NULL); + else + return (PptpCallId)(hptr + 1); +} + + +int +AliasHandlePptpGreOut(struct ip *pip) +{ + GreHdr *gr; + struct alias_link *link; + + gr = (GreHdr *)((char *)pip + (pip->ip_hl << 2)); + + /* Check GRE header bits. */ + if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE) + return (-1); + + link = FindPptpOutByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id); + if (link != NULL) { + struct in_addr alias_addr = GetAliasAddress(link); + + /* Change source IP address. */ + DifferentialChecksum(&pip->ip_sum, + (u_short *)&alias_addr, + (u_short *)&pip->ip_src, + 2); + pip->ip_src = alias_addr; + } + + return (0); +} + + +int +AliasHandlePptpGreIn(struct ip *pip) +{ + GreHdr *gr; + struct alias_link *link; + + gr = (GreHdr *)((char *)pip + (pip->ip_hl << 2)); + + /* Check GRE header bits. */ + if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE) + return (-1); + + link = FindPptpInByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id); + if (link != NULL) { + struct in_addr src_addr = GetOriginalAddress(link); + + /* De-alias the Peer's Call Id. */ + gr->gh_call_id = GetOriginalPort(link); + + /* Restore original IP address. */ + DifferentialChecksum(&pip->ip_sum, + (u_short *)&src_addr, + (u_short *)&pip->ip_dst, + 2); + pip->ip_dst = src_addr; + } + + return (0); +} |
