pkg/55845: pkgin may cause pkg_add to dump core

[he%NetBSD.org@localhost]

>Number:         55845
>Category:       pkg
>Synopsis:       pkgin may cause pkg_add to dump core
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 05 12:40:00 +0000 2020
>Originator:     he%NetBSD.org@localhost
>Release:        NetBSD 9.0_STABLE
>Organization:
	I try...
>Environment:
	
	
System: NetBSD smistad.uninett.no 9.0_STABLE NetBSD 9.0_STABLE (GENERIC) #0: Sat May 30 02:09:41 CEST 2020 he%smistad.uninett.no@localhost:/usr/obj/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:

	I had postgres95-client installed, but in a pkg upgrade to
	2020Q3 packages, pkgin wanted to install postgresql12-client
	instead.  This was installed as a dependency of
	p5-DBD-postgresql, so when trying to reinstall that without
	tidying up the old posgresql95-client package, I experienced
	this:

# pkgin in p5-DBD-postgresql
calculating dependencies...done.
postgresql12-client-12.4nb1 (to be installed) conflicts with installed package postgresql95-client-9.5.23nb1.
proceed ? [y/N] n
Segmentation fault (core dumped)
# pkg_info | grep pkgin
pkgin-20.8.0        Apt / yum like tool for managing pkgsrc binary packages
#
# ls -l *.core
-rw-------  1 root  wsrc  4885936 Dec  4 14:33 pkg_add.core
# 

	What?!?  Why would pkgin run pkg_add behind my back when I
	said that pkgin should *not* proceed?

	I *think* pkgin uses /usr/pkg/sbin/pkg_add (not sure), if so
	this points to a string comparison against ... null? 

# gdb /usr/pkg/sbin/pkg_add pkg_add.core
...
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000074a4d756b490 in strcmp () from /usr/lib/libc.so.12
(gdb) where
#0  0x000074a4d756b490 in strcmp () from /usr/lib/libc.so.12
#1  0x0000000000440147 in check_dependencies ()
#2  0x0000000000407a33 in pkg_do ()
#3  0x000000000040805f in pkg_perform ()
#4  0x0000000000440440 in main ()
(gdb)

(gdb) i reg
...
rdi            0xfffffffffffffff8  -8
...
rip            0x74a4d756b490      0x74a4d756b490 <strcmp+64>
...
(gdb) x/i 0x74a4d756b490
=> 0x74a4d756b490 <strcmp+64>:  mov    0x8(%rdi),%rax
(gdb) 


>How-To-Repeat:
	Have an old p5-DBD-postgresql installed, together with an old
	postgres95-client package.

>Fix:
	Sorry, no suggestion here.

>Unformatted: