clear passwords with explicit_bzero

Make sure to explicitly clear memory that is used for password input. memset
is often optimized out by the compiler.

Brought to attention by the OpenBSD community, see:
https://marc.info/?t=146989502600003&r=1&w=2
Thread subject: x11/slock: clear passwords with explicit_bzero

Changes:

- explicit_bzero.c import from libressl-portable.
- Makefile: add COMPATSRC for compatibility src.
- config.mk: add separate *BSD section in config.mk to simply uncomment it on
  these platforms.

1 files changed, 3 insertions, 3 deletions

diff --git a/Makefile b/Makefile
index 86b3437..8b3e248 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@
 
 include config.mk
 
-SRC = slock.c
+SRC = slock.c ${COMPATSRC}
 OBJ = ${SRC:.c=.o}
 
 all: options slock
@@ -35,8 +35,8 @@ clean:
 dist: clean
         @echo creating dist tarball
         @mkdir -p slock-${VERSION}
-        @cp -R LICENSE Makefile README config.def.h config.mk ${SRC} slock.1 \
-                slock-${VERSION}
+        @cp -R LICENSE Makefile README config.def.h config.mk ${SRC} \
+                explicit_bzero.c slock.1 slock-${VERSION}
         @tar -cf slock-${VERSION}.tar slock-${VERSION}
         @gzip slock-${VERSION}.tar
         @rm -rf slock-${VERSION}