kern/123965: tcpdump does not see outgoing RST when pf is enabled

[Kian Mohageri]

>Number:         123965
>Category:       kern
>Synopsis:       tcpdump does not see outgoing RST when pf is enabled
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat May 24 21:50:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Kian Mohageri
>Release:        FreeBSD 7.0-RELEASE i386
>Organization:
>Environment:
System: FreeBSD alvis.restek.wwu.edu 7.0-RELEASE FreeBSD 7.0-RELEASE #0: Sat Mar 1 17:41:33 PST 2008 root at alvis.restek.wwu.edu:/usr/obj/usr/src/sys/GENERIC i386

>Description:
When pf is enabled, block-policy is 'return', and a packet is blocked, pf sends a RST but tcpdump never sees it.

>How-To-Repeat:

 - Enable pf with 'set block-policy return' and rules to deny traffic
 - Start tcpdump on your FreeBSD 7 host
 - Try to connect to FreeBSD 7 host from somewhere (that will be rejected)
 - Notice that tcpdump sees the incoming SYN but not the outgoing RST
 - Disable pf and try again
 - Notice that tcpdump correctly sees both the SYN and the RST

In both cases, the RST *is* originating from the FreeBSD 7 host - that can be verified by tcpdumping on intermediate routers/firewalls.

If it's at all helpful information, a FreeBSD 6.3 host sees the SYN/RST in both cases.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: