Raspberry5 mailformed TFTP ACK packets

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
raspberry-pi
Domain
embedded-iot, networking

Research direction

Start by inspecting the linked raspberry5_ack.pcapng.gz capture, or the referenced raspberry5_ack_pad.pcapng.gz file, with the filter tftp.opcode == 4. Compare the Raspberry 5 ACK packet structure with Raspberry 4 behavior; done means identifying and correcting the bootloader behavior that adds zero padding beyond the UDP length.

Written by the indexing model from the issue text.

Description

At netboot, a Raspberry5 board sends malformed UDP packets padded with zeros while pulling resources from the TFTP server. As it may be seen in the raspberry5_ack_pad.pcapng.gz, a Raspberry 5 may acknowledge a TFTP data packet with ACK being padded with zeros. While it does not affect the boot process because the UDP length field is set to correct length, it is still an incorrect bootloader behavior.

raspberry5_ack.pcapng.gz

Filter: tftp.opcode == 4

That behavior has never happened with Raspberry 4 boards.

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