slock

simple X display locker utility
git clone git://git.suckless.org/slock
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commit a7afade1701a809f6a33b53525d59dd29b38d381
parent 65b8d5278882310eed758e6fbfd6ab9676db883c
Author: Hiltjo Posthuma <hiltjo@codemadness.org>
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:
Makefile | 6+++---
config.mk | 4++++
explicit_bzero.c | 19+++++++++++++++++++
slock.c | 8++++++--
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${X11LIB} -lX11 -lXext -lXrandr CPPFLAGS = -DVERSION=\"${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, 0); 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 < sizeof(passwd))) { diff --git a/util.h b/util.h @@ -0,0 +1,2 @@ +#undef explicit_bzero +void explicit_bzero(void *, size_t);