accf_dns.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (C) 2007 David Malone <dwmalone@FreeBSD.org>
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  *
   28  *      $FreeBSD$
   29  */
   30 
   31 #define ACCEPT_FILTER_MOD
   32 
   33 #include <sys/param.h>
   34 #include <sys/kernel.h>
   35 #include <sys/mbuf.h>
   36 #include <sys/module.h>
   37 #include <sys/signalvar.h>
   38 #include <sys/sysctl.h>
   39 #include <sys/socketvar.h>
   40 
   41 /* check for full DNS request */
   42 static int sohasdns(struct socket *so, void *arg, int waitflag);
   43 
   44 ACCEPT_FILTER_DEFINE(accf_dns, "dnsready", sohasdns, NULL, NULL, 1);
   45 
   46 struct packet {
   47         struct mbuf *m;         /* Current mbuf. */
   48         struct mbuf *n;         /* nextpkt mbuf. */
   49         unsigned long moff;     /* Offset of the beginning of m. */
   50         unsigned long offset;   /* Which offset we are working at. */
   51         unsigned long len;      /* The number of bytes we have to play with. */
   52 };
   53 
   54 #define DNS_OK 0
   55 #define DNS_WAIT -1
   56 #define DNS_RUN -2
   57 
   58 /* check we can skip over various parts of DNS request */
   59 static int skippacket(struct sockbuf *sb);
   60 
   61 static int
   62 sohasdns(struct socket *so, void *arg, int waitflag)
   63 {
   64         struct sockbuf *sb = &so->so_rcv;
   65 
   66         /* If the socket is full, we're ready. */
   67         if (sbused(sb) >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax)
   68                 goto ready;
   69 
   70         /* Check to see if we have a request. */
   71         if (skippacket(sb) == DNS_WAIT)
   72                 return (SU_OK);
   73 
   74 ready:
   75         return (SU_ISCONNECTED);
   76 }
   77 
   78 #define GET8(p, val) do { \
   79         if (p->offset < p->moff) \
   80                 return DNS_RUN; \
   81         while (p->offset >= p->moff + p->m->m_len) { \
   82                 p->moff += p->m->m_len; \
   83                 p->m = p->m->m_next; \
   84                 if (p->m == NULL) { \
   85                         p->m = p->n; \
   86                         p->n = p->m->m_nextpkt; \
   87                 } \
   88                 if (p->m == NULL) \
   89                         return DNS_WAIT; \
   90         } \
   91         val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \
   92         p->offset++; \
   93         } while (0)
   94 
   95 #define GET16(p, val) do { \
   96         unsigned int v0, v1; \
   97         GET8(p, v0); \
   98         GET8(p, v1); \
   99         val = v0 * 0x100 + v1; \
  100         } while (0)
  101 
  102 static int
  103 skippacket(struct sockbuf *sb) {
  104         unsigned long packlen;
  105         struct packet q, *p = &q;
  106 
  107         if (sbavail(sb) < 2)
  108                 return DNS_WAIT;
  109 
  110         q.m = sb->sb_mb;
  111         q.n = q.m->m_nextpkt;
  112         q.moff = 0;
  113         q.offset = 0;
  114         q.len = sbavail(sb);
  115 
  116         GET16(p, packlen);
  117         if (packlen + 2 > q.len)
  118                 return DNS_WAIT;
  119 
  120         return DNS_OK;
  121 }

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FreeBSD/Linux Kernel Cross Reference sys/netinet/accf_dns.c

FreeBSD/Linux Kernel Cross Reference
sys/netinet/accf_dns.c