The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet/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: releng/12.0/sys/netinet/accf_dns.c 326272 2017-11-27 15:23:17Z pfg $
   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 struct packet {
   45         struct mbuf *m;         /* Current mbuf. */
   46         struct mbuf *n;         /* nextpkt mbuf. */
   47         unsigned long moff;     /* Offset of the beginning of m. */
   48         unsigned long offset;   /* Which offset we are working at. */
   49         unsigned long len;      /* The number of bytes we have to play with. */
   50 };
   51 
   52 #define DNS_OK 0
   53 #define DNS_WAIT -1
   54 #define DNS_RUN -2
   55 
   56 /* check we can skip over various parts of DNS request */
   57 static int skippacket(struct sockbuf *sb);
   58 
   59 static struct accept_filter accf_dns_filter = {
   60         "dnsready",
   61         sohasdns,
   62         NULL,
   63         NULL
   64 };
   65 
   66 static moduledata_t accf_dns_mod = {
   67         "accf_dns",
   68         accept_filt_generic_mod_event,
   69         &accf_dns_filter
   70 };
   71 
   72 DECLARE_MODULE(accf_dns, accf_dns_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);
   73 
   74 static int
   75 sohasdns(struct socket *so, void *arg, int waitflag)
   76 {
   77         struct sockbuf *sb = &so->so_rcv;
   78 
   79         /* If the socket is full, we're ready. */
   80         if (sbused(sb) >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax)
   81                 goto ready;
   82 
   83         /* Check to see if we have a request. */
   84         if (skippacket(sb) == DNS_WAIT)
   85                 return (SU_OK);
   86 
   87 ready:
   88         return (SU_ISCONNECTED);
   89 }
   90 
   91 #define GET8(p, val) do { \
   92         if (p->offset < p->moff) \
   93                 return DNS_RUN; \
   94         while (p->offset >= p->moff + p->m->m_len) { \
   95                 p->moff += p->m->m_len; \
   96                 p->m = p->m->m_next; \
   97                 if (p->m == NULL) { \
   98                         p->m = p->n; \
   99                         p->n = p->m->m_nextpkt; \
  100                 } \
  101                 if (p->m == NULL) \
  102                         return DNS_WAIT; \
  103         } \
  104         val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \
  105         p->offset++; \
  106         } while (0)
  107 
  108 #define GET16(p, val) do { \
  109         unsigned int v0, v1; \
  110         GET8(p, v0); \
  111         GET8(p, v1); \
  112         val = v0 * 0x100 + v1; \
  113         } while (0)
  114 
  115 static int
  116 skippacket(struct sockbuf *sb) {
  117         unsigned long packlen;
  118         struct packet q, *p = &q;
  119 
  120         if (sbavail(sb) < 2)
  121                 return DNS_WAIT;
  122 
  123         q.m = sb->sb_mb;
  124         q.n = q.m->m_nextpkt;
  125         q.moff = 0;
  126         q.offset = 0;
  127         q.len = sbavail(sb);
  128 
  129         GET16(p, packlen);
  130         if (packlen + 2 > q.len)
  131                 return DNS_WAIT;
  132 
  133         return DNS_OK;
  134 }

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