TFTP hangs with fragmented IP packets

[Laurent Pinchart]

Hi Ramon,

On Sun, Apr 03, 2022 at 02:17:26AM +0300, Ramon Fried wrote:
> On Thu, Mar 31, 2022 at 8:43 AM Ramon Fried wrote:
> > On Tue, Mar 29, 2022 at 11:28 PM Laurent Pinchart wrote:
> > >
> > > Hello,
> > >
> > > I've banged my head a few days ago trying to debug an issue with a TFTP
> > > transfer hanging in the middle.
> > >
> > > I'm testing U-Boot 2022-rc5 on a Toradex Verdin i.MX8MP module (using
> > > the verdin-imx8mp defconfig). My local network MTU is 1500 bytes, and
> > > the board uses the EQoS ethernet controller.
> > >
> > > The problem started occurring after rebuilding a kernel image. U-Boot
> > > started transferring the image, and stopped in the middle, eventually
> > > timing out. Capture network traffic showed that U-Boot was continuously
> > > asking for retransmit of the same block, and eventually timed out.
> > >
> > > U-Boot is configured with a default TFTP block size of 4096 bytes, which
> > > results in the TFTP blocks being sent in one UDP packet split in three
> > > IP packets. U-Boot is configured with IP fragmentation supprot enabled.
> > > This works fine for all TFTP blocks until a paticular one in the middle
> > > of the kernel image.
> > >
> > > I've narrowed it down to a file of 1472 that can't be transferred at
> > > all (I have attached the binary to this e-mail). Changing the value of
> > > any of the last two bytes of the file allows transferring it correctly,
> > > so I suspect a CRC issue, likely related to IP fragmentation. Lowering
> > > the TFTP block size to avoid fragmentation works around the problem.
> > >
> > > Arguably a TFTP block size of 4096 bytes should probably not be used
> > > with a 1500 bytes MTU network, but I thought it would be useful to fix
> > > the issue nonetheless.
> > >
> > > I can test patches.
> > >
> > Interesting.
> > I will try to reproduce.
> > Thanks for reporting.
> 
> Hi.
> I couldn't reproduce the issue with the file you provided.
> I used sandbox64, and changed the TFTP BLOCK size to 4096.
> I managed to TFTP the file successfully.
> 
> => setenv autoload no
> => setenv ethrotate no
> => setenv ethact eth0
> => setenv ipaddr
> => setenv serverip 172.23.1.137
> => env set ipaddr 172.23.1.100
> => tftpboot 0x100000 test.bin
> Using host_eno1 device
> TFTP from server 172.23.1.137; our IP address is 172.23.1.100
> Filename 'test.bin'.
> Load address: 0x100000
> Loading: #
>          718.8 KiB/s
> done
> Bytes transferred = 1472 (5c0 hex)
> =>

Hmmmm... I wonder if it could be specific to the EQoS ethernet
controller in the i.MX8, maybe caused by issues in hardware CRC
calculation ? I don't have any other board I can use for testing this at
the moment as I'm travelling.

> Can you perhaps send me a network PCAP of your device failing to
> digest the file ?

I'll try to do that tomorrow.

-- 
Regards,

Laurent Pinchart