bin/48554: tcpdump -w does not work

[martin%NetBSD.org@localhost]

>Number:         48554
>Category:       bin
>Synopsis:       tcpdump -w does not work
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jan 27 12:40:00 +0000 2014
>Originator:     Martin Husemann
>Release:        NetBSD 6.99.30
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD night-owl.duskware.de 6.99.30 NetBSD 6.99.30 (NIGHT-OWL) #223: 
Sun Jan 26 12:14:48 CET 2014 
martin%night-owl.duskware.de@localhost:/usr/src/sys/arch/amd64/compile/NIGHT-OWL
 amd64
Architecture: x86_64
Machine: amd64
>Description:

tcpdump is unable to write capture files (for further analysis with wireshark
for example):

 # tcpdump -i wm0 -w /tmp/client.cap
 tcpdump: /tmp/client.cap: No such file or directory

checking ktrace output shows that at the time of the open() call, tcpdump
is already chrooted to /var/chroot/tcpdump (which is owned by root and mode
0755), and also setuser _tcpdump. This causes even local paths (./client.cap)
to fail.

Tcpdump should open the output file before the chroot, everything else is
going to confuse the user.

>How-To-Repeat:
s/a

>Fix:
n/a