[lwip-devel] [bug #34534] Error in sending fragmented IP if MEM_ALIGNMENT > 1

[Andriy Korud]

URL:
  <http://savannah.nongnu.org/bugs/?34534>

                 Summary: Error in sending fragmented IP if MEM_ALIGNMENT > 1
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: akorud
            Submitted on: Wed 12 Oct 2011 05:49:20 AM GMT
                Category: IPv4
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 
            lwIP version: 1.4.0

    _______________________________________________________

Details:

Hi, I've discovered that this change "Fixed bug #29361 (ip_frag has problems
with zero-copy DMA MACs) by adding custom pbufs and implementing custom pbufs
that reference other (original) pbufs." has introduced new problem. 
In line 379 in pbuf.c new custom pbuf is referenced with alignment, resulting
wrong data to be sent. In ip_frag() too chained pbuf's are created for each
fragment: for header and payload. Header takes 20 bytes and payload instead to
be referenced to position +20, points to byte at +32 (MEM_ALIGNMENT 32). This
cause bytes in range 20..31 are not sent at all. 
How to reproduce: set MEM_ALIGNMENT to 32 and try to ping with packets > MTU.
Ping replies will return corrupted. 
Temporary solution (works for me) - rollback mentioned change. Probably
removing p->pbuf.payload = LWIP_MEM_ALIGN((void *)((u8_t *)payload_mem +
offset)); will also work, I'm not sure of side effects. 




    _______________________________________________________

Reply to this item at:

  <http://savannah.nongnu.org/bugs/?34534>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.nongnu.org/