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	clear passwords with explicit_bzero - slock - simple X display locker utility
	git clone git://git.suckless.org/slock
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	---
	commit a7afade1701a809f6a33b53525d59dd29b38d381
	parent 65b8d5278882310eed758e6fbfd6ab9676db883c
	Author: Hiltjo Posthuma <[email protected]>
	Date: Sun, 31 Jul 2016 13:43:00 +0200

	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.

	Diffstat:
	M Makefile \| 6 +++---
	M config.mk \| 4 ++++
	A explicit_bzero.c \| 19 +++++++++++++++++++
	M slock.c \| 8 ++++++--
	A util.h \| 2 ++

	5 files changed, 34 insertions(+), 5 deletions(-)
	---
	diff --git 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}
	diff --git a/config.mk b/config.mk
	@@ -18,9 +18,13 @@ LIBS = -L/usr/lib -lc -lcrypt -L${X11LIB} -lX11 -lXext -lXra…
	CPPFLAGS = -DVERSION=\"${VERSION}\" -DHAVE_SHADOW_H
	CFLAGS = -std=c99 -pedantic -Wall -Os ${INCS} ${CPPFLAGS}
	LDFLAGS = -s ${LIBS}
	+COMPATSRC = explicit_bzero.c

	# On *BSD remove -DHAVE_SHADOW_H from CPPFLAGS and add -DHAVE_BSD_AUTH
	# On OpenBSD and Darwin remove -lcrypt from LIBS
	+#LIBS = -L/usr/lib -lc -L${X11LIB} -lX11 -lXext -lXrandr
	+#CPPFLAGS = -DVERSION=\"${VERSION}\" -DHAVE_BSD_AUTH -D_BSD_SOURCE
	+#COMPATSRC =

	# compiler and linker
	CC = cc
	diff --git a/explicit_bzero.c b/explicit_bzero.c
	@@ -0,0 +1,19 @@
	+/* $OpenBSD: explicit_bzero.c,v 1.3 2014/06/21 02:34:26 matthew Exp $ */
	+/*
	+ * Public domain.
	+ * Written by Matthew Dempsky.
	+ */
	+
	+#include <string.h>
	+
	+__attribute__((weak)) void
	+__explicit_bzero_hook(void *buf, size_t len)
	+{
	+}
	+
	+void
	+explicit_bzero(void *buf, size_t len)
	+{
	+ memset(buf, 0, len);
	+ __explicit_bzero_hook(buf, len);
	+}
	diff --git a/slock.c b/slock.c
	@@ -23,6 +23,8 @@
	#include <bsd_auth.h>
	#endif

	+#include "util.h"
	+
	enum {
	INIT,
	INPUT,
	@@ -135,7 +137,7 @@ readpw(Display dpy, const char pws)
	* timeout. */
	while (running && !XNextEvent(dpy, &ev)) {
	if (ev.type == KeyPress) {
	- buf[0] = 0;
	+ explicit_bzero(&buf, sizeof(buf));
	num = XLookupString(&ev.xkey, buf, sizeof(buf), &ksym,…
	if (IsKeypadKey(ksym)) {
	if (ksym == XK_KP_Enter)
	@@ -161,14 +163,16 @@ readpw(Display dpy, const char pws)
	XBell(dpy, 100);
	failure = True;
	}
	+ explicit_bzero(&passwd, sizeof(passwd));
	len = 0;
	break;
	case XK_Escape:
	+ explicit_bzero(&passwd, sizeof(passwd));
	len = 0;
	break;
	case XK_BackSpace:
	if (len)
	- --len;
	+ passwd[len--] = 0;
	break;
	default:
	if (num && !iscntrl((int)buf[0]) && (len + num…
	diff --git a/util.h b/util.h
	@@ -0,0 +1,2 @@
	+#undef explicit_bzero
	+void explicit_bzero(void *, size_t);