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lib/55143: pflogd uses internal libpcap state

>Number:         55143
>Category:       lib
>Synopsis:       pflogd uses internal libpcap state
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Apr 05 06:25:00 +0000 2020
>Originator:     Martin Husemann
>Release:        NetBSD 9.99.52
The NetBSD Foundation, Inc.
System: NetBSD 9.99.52 NetBSD 9.99.52 (GENERIC) #378: Tue Mar 31 11:09:27 CEST 2020 amd64
Architecture: x86_64
Machine: amd64

Pflogd is compiled against libpcap:

        -lpcap.8 => /lib/
        -lc.12 => /lib/
        -lutil.7 => /lib/

and it abuses internal state from it, noticable if you remove the include of
(the not publically installed header) pcap-int.h from the source:

/work/src/dist/pf/sbin/pflogd/privsep.c: In function 'set_snaplen':
/work/src/dist/pf/sbin/pflogd/privsep.c:200:7: error: dereferencing pointer to incomplete type 'pcap_t' {aka 'struct pcap'}
  hpcap->snapshot = snap;
Now unfortunately libpcap has an #ifdef ENABLE_REMOTE in that struct, and
it is not defined when compiling pflogd, but is compiled when compiling
our in-tree libpcap.

This means the pcap_t seen by pflogd differs from the pcap_t actually created
and populated by libpcap. And even more unfortunate, the "snapshot" member
is later in the structure than the #ifdef'd part, so pflogd will actually
set hpcap->linktype_ext instead of hpcap->snapshot.

Code inspection (actually found by a #else #error added to pcap-int.h and
the #ifdef ENABLE_REMOTE clause)

One of:
 1) avoid using pcap internal state in pflogd (unfortunately there seems to
    be only a query function for snapshot, not a set function)
 2) add -DENABLE_REMOTE to the pflogd compilation
 3) remove the #ifdef from pcap-int.h
 4) remove pflogd

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