use a safer idiom for reading pid from file before killing

pointed out by kn, tested in snaps for a week

diff --git a/distrib/miniroot/install.sub b/distrib/miniroot/install.sub
index 33c9e6d..dd910db 100644 (file)
--- a/distrib/miniroot/install.sub
+++ b/distrib/miniroot/install.sub
@@ -1,5 +1,5 @@
 #!/bin/ksh
-#      $OpenBSD: install.sub,v 1.1198 2022/05/09 22:43:57 deraadt Exp $
+#      $OpenBSD: install.sub,v 1.1199 2022/05/16 00:27:46 deraadt Exp $
 #
 # Copyright (c) 1997-2015 Todd Miller, Theo de Raadt, Ken Westerback
 # Copyright (c) 2015, Robert Peichaer <rpe@openbsd.org>
@@ -543,7 +543,7 @@ unlock() {
 
 # Add a trap to kill the dmesg listener co-process on exit of the installer.
 retrap() {
-       trap 'if [ -f /tmp/cppid ]; then kill -KILL -$(cat /tmp/cppid) 2>/dev/null; rm -f /tmp/cppid; fi; echo; stty echo; exit 0' \
+       trap '_cppid=$(</tmp/cppid); if [ -n $_cppid ]; then kill -KILL -$_cppid 2>/dev/null; rm -f /tmp/cppid; fi; echo; stty echo; exit 0' \
                INT EXIT TERM
 }