IP address in the kernel

[Jeremy Andrus <jandru39@calvin.edu>]

OK. I've written some code based on Trevor Hamm's suggestions, but it 
segfaults. Here's what I have:

----- BEGIN CODE -----
  struct in_device *in_dev;
  struct in_ifaddr **ifap = NULL;
  struct in_ifaddr *ifa = NULL;
  struct net_device *dev;
  struct in_addr in;
  unsigned long pci_ip_dword;
  char iname[4];

  strcpy(iname, "eth0");
  if ( (dev = dev_get_by_name(iname)) == NULL ) {
    printk("  |--> Couldn't find a network interface.\n");
    printk("       You need at least one interface (eth0) for this 
netfilter hook to work.\n");
    return 0;
  }
  printk("Looking for 'eth0' . . .\n");
  if ( (in_dev = in_dev_get(dev)) != NULL ) {
    if (ifa == NULL) {
      for (ifap=&in_dev->ifa_list; (ifa=*ifap) != NULL; 
ifap=&ifa->ifa_next)
        if (strcmp(iname, ifa->ifa_label) == 0)
           break;
    }
  }

  printk("making dword . . .\n");
  in.s_addr = ifa->ifa_local;
  pci_ip_dword = (unsigned long)in.s_addr;
  pci_ip_dword = (pci_ip_dword << 15);
  pci_ip_dword = (pci_ip_dword & 0x7F800000);
  printk("My IP address dword is: %lx\n", (unsigned long)pci_ip_dword);

----- END CODE -----

When I modprobe my netfilter target, dmesg has this in it:

----- BEGIN DMESG DUMP -----
Looking for 'eth0' . . .
making dword . . .
My IP address dword is: 54000000
making a note of it . . .
Unable to handle kernel NULL pointer dereference at virtual address 
00000011
 printing eip:
e0840a02
*pde = 00000000
Oops: 0002
CPU:    0
EIP:    0010:[<e0840a02>]    Not tainted
EFLAGS: 00010286
eax: 00000001   ebx: e08480b0   ecx: 30687465   edx: 00000001
esi: 00000070   edi: e0848040   ebp: 00000000   esp: def73d74
ds: 0018   es: 0018   ss: 0018
Process iptables (pid: 102, stackpage=def73000)
Stack: def73e08 e0848040 e08480d0 00000000 00000002 00000000 00000163 
e084a040 
       00000000 def73dc0 e084b000 c0126c4f def73dc0 00000000 e084833c 
e0848040 
       00000000 0004b000 00000000 00000000 e0841149 def73e08 0000000e 
e0848000 
Call Trace: [<c0126c4f>] [<e0841149>] [<e084161b>] [<e0842880>] 
[<c01bf540>] 
   [<c01bf5a2>] [<c01cabef>] [<c010ff03>] [<c01e0318>] [<c01e5c7a>] 
[<c01b42f1>] 
   [<c01b4996>] [<c0106c5b>] 

Code: ff 40 10 8b 42 34 80 48 14 18 89 53 04 b9 80 27 84 e0 ff 05 

----- END DMESG DUMP -----

The pci_ip_dword isn't correct either. Grrrr. Kernel hacking. Grrrr.

	-Jeremy 


-- 
----------------------------
Jeremy C. Andrus
http://www.jeremya.com/
----------------------------
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