Could you have a look at kern/63961

[Christian S.J. Peron]

Hey Andre,

I took a quick look at the PR and I dont think this is a bug.
If you want to match setup packets for TCP connections it
does work, but only if the connection has a PCB associated with it.
For instance, outgoing setup would have a PCB associated with it,
so ipfw could match on that:

dev0# ipfw show
00400     1      64 count tcp from any to any dst-port 4296 setup uid csjp

It should be noted that all the "setup" keyword does is set the
O_TCPFLAGS opcode and set the operand to TH_SYN for SYN packets.
I dont think Incoming TCP connection requests would not have a
PCB associated with it, so there is no-way that ipfw can look
up the credential associated with it.

However the UID negation problem looks like it could be a bug
either in how ipfw(8) reports the rule or how the kernel is
processing it. In either case I will look into it.

-- 
Christian S.J. Peron
csjp at FreeBSD.ORG
FreeBSD Committer