From: Lothar > 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.
I understood the bug. The point I was making is that if you have to do a read-write of the received data (to byteswap it) then you might as well always copy it into a new skb that is just big enough for the actual receive frame. David