Re: dlil_inject_if_input
Re: dlil_inject_if_input
- Subject: Re: dlil_inject_if_input
- From: Justin Walker <email@hidden>
- Date: Fri, 17 Sep 2004 22:39:33 -0700
On Sep 17, 2004, at 21:55, Matt Jaffa wrote:
Here is how I am formulating my IP header:
ipHeader is the ip header pulled out from the mbuf that I am not
letting out into the internet.
struct ip* newip = (struct ip*)_MALLOC(sizeof(struct
ip),M_FREE,M_NOWAIT);
Why are you using _MALLOC instead of (say) MGET? You may be asking for
trouble here, unless you are taking care of properly releasing this
storage.
newip->ip_hl = 5;
newip->ip_v = ipHeader->ip_v;
printf("ipHeader version: %d\n", ipHeader->ip_v);
printf("ipHeader hdrleng: %d\n", ipHeader->ip_hl);
printf("newipheader: %d\n", newip->ip_v);
printf("newipheader: %d\n", newip->ip_hl);
Well, what do the printf's say? FWIW, the kernel code defines _IP_VHL,
and refers to the two fields as the combined field 'ip_vhl'. Why not
print a hex dump of the first few bytes of the two IP headers? That
may provide a clue (and it avoids any funky behavior based on bit-field
operations).
newip->ip_tos = 0;
int data_len = strlen(httpresponse); // this is the
HTTP/1.1 response length of the tcp data I will inject into the input
I assume the length of this canned response is small enough that you
don't have to worry about overflowing whatever you are using for
buffers.
newip->ip_len = sizeof(struct ip) + sizeof(struct tcphdr) +
data_len;
newip->ip_id = 34234;
newip->ip_off = 0x4000;
BTW, I would set ip_off to zero.
newip->ip_ttl = 35;
newip->ip_p = ipHeader->ip_p;
newip->ip_sum = 0;
You compute the checksum later, right?
memcpy(&(newip->ip_src), &(ipHeader->ip_dst), sizeof(struct
in_addr));
memcpy(&(newip->ip_dst), &(ipHeader->ip_src), sizeof(struct
in_addr));
For correctness, you might want to assure that the values you are
copying are in network order (since the IP stack has set it up that way
on output). For PowerPC, host order and network order are the same,
but it pays to keep this straight in your code.
despite the fact that some of the other stuff might be wrong, why
wouldn't the ip_v be the right version? The output does print out 4
like it should be.
Any number of things could be wrong. One obvious possibility is that
when you finally cons up the frame you inject, you aren't matching the
assumptions of the input processing, so that when that code looks looks
at the IP header, it's not seeing your IP header (e.g., there should be
an ethernet header, but isn't; or there is an ethernet header, but
there should not be one).
To emphasize a point above, do *not* allocate mbufs other than by MGET
(or similar call) unless you are actually obeying all the rules for
supplying your own buffers (and freeing same).
Regards,
Justin
--
Justin C. Walker, Curmudgeon-At-Large *
Institute for General Semantics | "Weaseling out of things is
what
| separates us from the animals.
| Well, except the weasel."
| - Homer J Simpson
*--------------------------------------*-------------------------------*
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