Page MenuHomeFreeBSD

Add ipfw protocol modification module ipfw_pmod

Authored by ae on Mar 27 2017, 1:51 PM.



This patch add new ipfw_pmod kernel module, that currently implements tcp-setmss rule action.
It sets TCP MSS value and supports both IPv4 and IPv6.

tcp-setmss rule works like setdscp rule. All TCP packets with SYN flag are matched, and if packet contains MSS TCP option, and its value is greater than specified in tcp-setmss VALUE, it modifies this value and updates TCP checksum if needed.

New O_EXTERNAL_DATA opcode added. It used together with O_EXTERNAL_ACTION opcode, but it does not require creating of some named instances, like O_EXTERNAL_INSTANCE opcode requires.

Later we can add some another opcodes with similar functional, but for different protocols to this ipfw_pmod module.

Test Plan

I tested the rule:

tcp-setmss 1300 tcp from any to any

for locally generated TCP traffic and for forwarded traffic, both IPv4 and IPv6. It modifies MSS value correctly.

Diff Detail

rS FreeBSD src repository - subversion
Automatic diff as part of commit; lint not applicable.
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

Modify some comments and error messages. Fix checksum modification
for forwarded traffic.

ae edited the test plan for this revision. (Show Details)
ae added reviewers: network, julian.
This revision was automatically updated to reflect the committed changes.
wblock added inline comments.
must be loaded or the kernel must have

s/original/the original/


s/specified/the specified/

The search continues with the next rule
regardless of whether a packet is matched by the
.Cm tcp-setmss