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[lwip-devel] [bug #36318] Wrong UDP data size for small datagrams


From: dagos
Subject: [lwip-devel] [bug #36318] Wrong UDP data size for small datagrams
Date: Thu, 26 Apr 2012 15:51:53 +0000
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:11.0) Gecko/20100101 Firefox/11.0

URL:
  <http://savannah.nongnu.org/bugs/?36318>

                 Summary: Wrong UDP data size for small datagrams
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: dagos
            Submitted on: jeu. 26 avril 2012 15:51:52 GMT
                Category: UDP
                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

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Details:

When a UDP datagram WITH PADDING is read by LWIP, p->tot_len includes padding
size.
This is wrong for 2 reasons:
- CheckSum calculation will fail (p->tot_len is used instead of UDP total size
field), and the paquet is rejected (if CHECKSUM_CHECK_UDP = 1)
- Data size given by p->tot_len is wrong so more data could be read by the
application.

To solve the problem, add in udp.c, l.114:
+ p->tot_len = ntohs(udphdr->len);  // DELETE PADDING





    _______________________________________________________

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