Re: RHEL 4.5 + brigde + sample QUEUE app=panic

[Scott MacKay <scottmackay@yahoo.com>]

More details....

The culprit seems to be the memcpy(), transferring the
payload back into the skb.
memcpy(e->skb->data, v->payload, v->data_len); 

I commented that out, and put a "return 0;"after:
 e->skb->nfcache |= NFC_ALTERED;

(basically skip the memcop and extra routing).  Worked
fine.

I now put in a for loop to run several different
tests.  It basically was:
        for (index=0;index<v->data_len;index++)  {
          /* insert test */
        }
First was:
    c=v->payload[index];  /* read the payload */
No crashes.
Second was:
    c=e->skb->data[index]; /* read the skb payload */
No crashes.
Next was:
    c=e->skb->data[index];  /* read sky payload */
    e->skb->data[index]=c;  /* write value back */
No crashes.
Now
    c=v->payload[index];
    e->skb->data[index]=c;
No crashes.
Finally:
    e->skb->data[index]=v->payload[index];
Crashes.

My test was with wget-ting a kernel and I would
actually see read errors appear before it finally
died.

I wil be retesting the final couple, but any idea why
in the world the memcpy and memcpy-ish loop would
crash everything?

-Scott


--- Scott MacKay <scottmackay@yahoo.com> wrote:

> Related to this:
> I got and rebuilt the ip_queue.c code and it seems
> to
> be within the ipq_mangle_ipv4 code.  The top part
> does
> not affect us since that is only for when size
> changes.  I commented out the mangle call (so I was
> still passing data down) and the system seemed to
> run
> ok, just like data_len=0.
> 
> When I reenabled the memcpy and the ALTER flag
> change
> it worked for a while but then locked up, the
> keyboard
> lights flashing.
> 
> Note that this did not always/immediately cause a
> crash but pretty close.  The last thing I could try
> is
> a simple for loop on the incoming data to see if
> accessing the data (like char c=payload[i] kind of
> throwaway) is the issue.  If there are any thoughts
> on
> the stuff sendmsg() sends to the ip_queue I would
> love
> to know.  
> 
> -Scott



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