Subject: Re: [PATCH] net: fec: fix regression on i.MX28 introduced by rx_copybreak support

From: Lothar Waßmann <[email-masked]>
Date: Tue, 7 Oct 2014 16:17:02 +0200

Hi,

David Laight wrote:
> From: Lothar Waßmann
> > commit 1b7bde6d659d ("net: fec: implement rx_copybreak to improve rx performance")
> > introduced a regression for i.MX28. The swap_buffer() function doing
> > the endian conversion of the received data on i.MX28 may access memory
> > beyond the actual packet size in the DMA buffer. fec_enet_copybreak()
> > does not copy those bytes, so that the last bytes of a packet may be
> > filled with invalid data after swapping.
> > This will likely lead to checksum errors on received packets.
> > E.g. when trying to mount an NFS rootfs:
> > UDP: bad checksum. From 192.168.1.225:111 to 192.168.100.73:44662 ulen 36
> > 
> > Do the byte swapping and copying to the new skb in one go if
> > necessary.
> 
> ISTM that if you need to do the 'swap' you should copy the data regardless
> of the length.
> 
The swap function has to look at at most 3 bytes beyond the actual
packet length. That is what the original swap_buffer() function does and
what the new function swap_buffer2(), that does the endian swapping
while copying to the new buffer, also does.

Lothar Waßmann
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