/* * 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 * * $FreeBSD: head/sys/netinet/libalias/alias_pptp.c 64334 2000-08-07 09:51:04Z ru $ */ /* 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 GRE alias link is created. The GRE 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 #include #include #include #include #include #include #include #include "alias_local.h" /* * PPTP definitions */ struct grehdr /* Enhanced GRE header. */ { u_char gh_recursion:3, /* Recursion control. */ gh_ssr_flag:1, /* Strict source route present. */ gh_seq_no_flag:1, /* Sequence number present. */ gh_key_flag:1, /* Key present. */ gh_rt_flag:1, /* Routing present. */ gh_cksum_flag:1; /* Checksum present. */ u_char gh_version:3, /* GRE version. */ gh_flags:4, /* Flags. */ gh_ack_no_flag:1; /* Acknowledgment sequence number present. */ u_short gh_protocol; /* Protocol type. */ u_short gh_length; /* Payload length. */ u_short gh_call_id; /* Call ID. */ u_int32_t gh_seq_no; /* Sequence number (optional). */ u_int32_t gh_ack_no; /* Acknowledgment number (optional). */ }; /* 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_statoReply = 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 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 *); int PptpGetCallID(struct ip *pip, u_short *call_id) { struct grehdr *gr; gr = (struct grehdr *)((char *)pip + (pip->ip_hl << 2)); /* Check GRE header bits. */ if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) == PPTP_INIT_VALUE) { *call_id = gr->gh_call_id; return 1; } else return 0; }; void PptpSetCallID(struct ip *pip, u_short call_id) { struct grehdr *gr; gr = (struct grehdr *)((char *)pip + (pip->ip_hl << 2)); gr->gh_call_id = call_id; }; void AliasHandlePptpOut(struct ip *pip, /* IP packet to examine/patch */ struct alias_link *link) /* The PPTP control link */ { struct alias_link *gre_link; PptpCallId cptr; 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 */ if ((ctl_type >= PPTP_OutCallRequest) && (ctl_type <= PPTP_CallDiscNotify)) { /* Establish GRE link for address and Call ID found in PPTP Control Msg */ gre_link = FindPptpOut(GetOriginalAddress(link), GetDestAddress(link), cptr->cid1); if (gre_link != NULL) { int accumulate = cptr->cid1; /* alias the Call Id */ cptr->cid1 = GetAliasPort(gre_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); } } } void AliasHandlePptpIn(struct ip *pip, /* IP packet to examine/patch */ struct alias_link *link) /* The PPTP control link */ { struct alias_link *gre_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; default: return; break; } /* Find GRE link for address and Call ID found in PPTP Control Msg */ gre_link = FindPptpIn(GetDestAddress(link), GetAliasAddress(link), *pcall_id); if (gre_link != NULL) { int accumulate = *pcall_id; /* alias the Call Id */ *pcall_id = GetOriginalPort(gre_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); } } 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); else return((PptpCallId)(((char *)hptr) + sizeof(struct pptpMsgHead))); }