netdev - [PATCH] AF_PACKET: Fix PACKET_MMAP on 64-bit kernel/32-bit user systems

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Message-ID: <20090810130359.p2hixk2eoow8kwg8@imap.linux.ibm.com>
Date:	Mon, 10 Aug 2009 13:03:59 -0400
From:	cndougla@...ux.vnet.ibm.com
To:	netdev@...r.kernel.org
Subject: [PATCH] AF_PACKET: Fix PACKET_MMAP on 64-bit kernel/32-bit user
	systems

PACKET_MMAP sets up a ring buffer at a memory location so that kernel  
and user space can read from it without extra overhead. However, the  
data is written with a header, struct tpacket_hdr, which begins with  
an unsigned long field, tp_status. This means in a split 64-bit/32-bit  
environment the kernel- and user-space reads from the mmap'd region  
will be different, since in kernel-space the field is 64-bit while in  
user-space the field is 32-bit.

The following patch makes the size of the structure constant by  
changing the tp_status field to 32-bits. It does not appear to need  
64-bits, since only 4-bits are actually used throughout the AF_PACKET  
code.

Signed-off-by: Chase Douglas <cndougla@...ux.vnet.ibm.com>
--- a/include/linux/if_packet.h   2009-08-10 16:53:11.000000000 +0000
+++ b/include/linux/if_packet.h   2009-08-10 16:53:28.000000000 +0000
@@ -65,7 +65,7 @@ struct tpacket_auxdata

  struct tpacket_hdr
  {
-       unsigned long   tp_status;
+       unsigned int    tp_status;
  #define TP_STATUS_KERNEL       0
  #define TP_STATUS_USER         1
  #define TP_STATUS_COPY         2

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