From 08ecfcb5b88569705ed760e97f28bf37613e7b3d Mon Sep 17 00:00:00 2001 From: otto <> Date: Fri, 27 Jun 2014 17:37:42 +0000 Subject: [PATCH] Move to a smaller rbytes buffer and skip a random part. Not to improve the random stream itself (it doesn't), but to introduce noise in the arc4random calling pattern. Thanks to matthew@ who pointed out bias in a previous diff, ok deraadt@ matthew@ --- src/lib/libc/stdlib/malloc.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/lib/libc/stdlib/malloc.c b/src/lib/libc/stdlib/malloc.c index ba8bd3ad..5d5437dc 100644 --- a/src/lib/libc/stdlib/malloc.c +++ b/src/lib/libc/stdlib/malloc.c @@ -1,4 +1,4 @@ -/* $OpenBSD: malloc.c,v 1.167 2014/06/02 08:49:38 otto Exp $ */ +/* $OpenBSD: malloc.c,v 1.168 2014/06/27 17:37:42 otto Exp $ */ /* * Copyright (c) 2008, 2010, 2011 Otto Moerbeek * Copyright (c) 2012 Matthew Dempsky @@ -118,7 +118,7 @@ struct dir_info { /* delayed free chunk slots */ void *delayed_chunks[MALLOC_DELAYED_CHUNK_MASK + 1]; size_t rbytesused; /* random bytes used */ - u_char rbytes[512]; /* random bytes */ + u_char rbytes[32]; /* random bytes */ u_short chunk_start; #ifdef MALLOC_STATS size_t inserts; @@ -276,7 +276,8 @@ static void rbytes_init(struct dir_info *d) { arc4random_buf(d->rbytes, sizeof(d->rbytes)); - d->rbytesused = 0; + /* add 1 to account for using d->rbytes[0] */ + d->rbytesused = 1 + d->rbytes[0] % (sizeof(d->rbytes) / 2); } static inline u_char