From d3d805ce3ba68be9a7f329129b705ba46ee50bc0 Mon Sep 17 00:00:00 2001 From: matthew <> Date: Fri, 24 Sep 2010 13:33:00 +0000 Subject: [PATCH] Add timingsafe_bcmp(3) to libc, mention that it's already in the kernel in kern(9), and remove it from OpenSSH. ok deraadt@, djm@ --- src/include/string.h | 3 ++- src/lib/libc/string/Makefile.inc | 6 +++-- src/lib/libc/string/bcmp.3 | 28 ++++++++++++++++++++--- src/lib/libc/string/timingsafe_bcmp.c | 33 +++++++++++++++++++++++++++ 4 files changed, 64 insertions(+), 6 deletions(-) create mode 100644 src/lib/libc/string/timingsafe_bcmp.c diff --git a/src/include/string.h b/src/include/string.h index e33204d9..3a1494d1 100644 --- a/src/include/string.h +++ b/src/include/string.h @@ -1,4 +1,4 @@ -/* $OpenBSD: string.h,v 1.19 2010/05/18 22:24:55 tedu Exp $ */ +/* $OpenBSD: string.h,v 1.20 2010/09/24 13:33:00 matthew Exp $ */ /* $NetBSD: string.h,v 1.6 1994/10/26 00:56:30 cgd Exp $ */ /*- @@ -124,6 +124,7 @@ size_t strlcpy(char *, const char *, size_t) void strmode(int, char *); char *strsep(char **, const char *); char *strsignal(int); +int timingsafe_bcmp(const void *, const void *, size_t); #endif __END_DECLS diff --git a/src/lib/libc/string/Makefile.inc b/src/lib/libc/string/Makefile.inc index 3264b799..34edd8eb 100644 --- a/src/lib/libc/string/Makefile.inc +++ b/src/lib/libc/string/Makefile.inc @@ -1,4 +1,4 @@ -# $OpenBSD: Makefile.inc,v 1.22 2010/05/18 22:24:55 tedu Exp $ +# $OpenBSD: Makefile.inc,v 1.23 2010/09/24 13:33:00 matthew Exp $ # string sources .PATH: ${LIBCSRCDIR}/arch/${MACHINE_CPU}/string ${LIBCSRCDIR}/string @@ -9,7 +9,8 @@ SRCS+= bm.c memccpy.c memrchr.c strcasecmp.c strcasestr.c strcoll.c strdup.c \ wcscat.c wcschr.c wcscmp.c wcscpy.c wcscspn.c wcslcat.c wcslcpy.c \ wcslen.c wcsncat.c wcsncmp.c wcsncpy.c wcspbrk.c wcsrchr.c wcsspn.c \ wcsstr.c wcstok.c wcswcs.c wcswidth.c wmemchr.c wmemcmp.c wmemcpy.c \ - wmemmove.c wmemset.c + wmemmove.c wmemset.c \ + timingsafe_bcmp.c # machine-dependent net sources # m-d Makefile.inc must include sources for: @@ -178,3 +179,4 @@ MLINKS+=wmemchr.3 wcspbrk.3 MLINKS+=wmemchr.3 wcsrchr.3 MLINKS+=wmemchr.3 wcsspn.3 MLINKS+=wmemchr.3 wcsstr.3 +MLINKS+=bcmp.3 timingsafe_bcmp.3 diff --git a/src/lib/libc/string/bcmp.3 b/src/lib/libc/string/bcmp.3 index 57e1a0fa..1a777506 100644 --- a/src/lib/libc/string/bcmp.3 +++ b/src/lib/libc/string/bcmp.3 @@ -27,18 +27,21 @@ .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" -.\" $OpenBSD: bcmp.3,v 1.7 2007/05/31 19:19:32 jmc Exp $ +.\" $OpenBSD: bcmp.3,v 1.8 2010/09/24 13:33:00 matthew Exp $ .\" -.Dd $Mdocdate: May 31 2007 $ +.Dd $Mdocdate: September 24 2010 $ .Dt BCMP 3 .Os .Sh NAME -.Nm bcmp +.Nm bcmp , +.Nm timingsafe_bcmp .Nd compare byte string .Sh SYNOPSIS .Fd #include .Ft int .Fn bcmp "const void *b1" "const void *b2" "size_t len" +.Ft int +.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len" .Sh DESCRIPTION The .Fn bcmp @@ -53,6 +56,20 @@ bytes long. Zero-length strings are always identical. .Pp The strings may overlap. +.Pp +The +.Fn timingsafe_bcmp +function has the same semantics as +.Fn bcmp , +but its running time is independent of the contents of +.Fa b1 +and +.Fa b2 , +making it safe to use for comparing secret values such as cryptographic MACs. +In contrast, +.Fn bcmp +returns after finding the first differing byte, +making it vulnerable to timing attacks. .Sh SEE ALSO .Xr memcmp 3 , .Xr strcasecmp 3 , @@ -64,3 +81,8 @@ A .Fn bcmp function first appeared in .Bx 4.2 . +.Pp +The +.Fn timingsafe_bcmp +function first appeared in +.Ox 4.9 . diff --git a/src/lib/libc/string/timingsafe_bcmp.c b/src/lib/libc/string/timingsafe_bcmp.c new file mode 100644 index 00000000..9c4287cf --- /dev/null +++ b/src/lib/libc/string/timingsafe_bcmp.c @@ -0,0 +1,33 @@ +/* $OpenBSD: timingsafe_bcmp.c,v 1.1 2010/09/24 13:33:00 matthew Exp $ */ +/* + * Copyright (c) 2010 Damien Miller. All rights reserved. + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#if !defined(_KERNEL) && !defined(_STANDALONE) +#include +#else +#include +#endif + +int +timingsafe_bcmp(const void *b1, const void *b2, size_t n) +{ + const unsigned char *p1 = b1, *p2 = b2; + int ret = 0; + + for (; n > 0; n--) + ret |= *p1++ ^ *p2++; + return (ret != 0); +}