Bug 215674

Summary:	ip_compute_csum computes illegal zero checksum, should return ffff in such a case
Product:	Networking	Reporter:	Eyal Lotem (eyal.lotem)
Component:	Other	Assignee:	Stephen Hemminger (stephen)
Status:	NEW ---
Severity:	normal
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	4.14.268	Subsystem:
Regression:	No	Bisected commit-id:

Description Eyal Lotem 2022-03-11 11:47:49 UTC

A 0 checksum indicates the checksum is to not be validated, and an 0xffff checksum indicates a zero result.

If the sum is computed to be 0, it should be substituted for 0xffff, to indicate the actual zero checksum.

This bug went unnoticed for a long time, because in 2^-16 of computed checksums, the incorrect result merely foregoes checksum validation, which is likely to not trigger any noticeable errors.