From ac398c3bafa6e4c80e20571373a96947db863b3d Mon Sep 17 00:00:00 2001 From: Lasse Collin Date: Sun, 13 Mar 2016 20:21:49 +0200 Subject: [PATCH] liblzma: Disable external SHA-256 by default. This is the sane thing to do. The conflict with OpenSSL on some OSes and especially that the OS-provided versions can be significantly slower makes it clear that it was a mistake to have the external SHA-256 support enabled by default. Those who want it can now pass --enable-external-sha256 to configure. INSTALL was updated with notes about OSes where this can be a bad idea. The SHA-256 detection code in configure.ac had some bugs that could lead to a build failure in some situations. These were fixed, although it doesn't matter that much now that the external SHA-256 is disabled by default. MINIX >= 3.2.0 uses NetBSD's libc and thus has SHA256_Init in libc instead of libutil. Support for the libutil version was removed. --- INSTALL | 36 +++++++++++++++++++ configure.ac | 76 +++++++++++++++++++-------------------- src/liblzma/check/check.h | 16 ++++----- 3 files changed, 79 insertions(+), 49 deletions(-) diff --git a/INSTALL b/INSTALL index 22ef0773..fb2b6d7c 100644 --- a/INSTALL +++ b/INSTALL @@ -246,6 +246,42 @@ XZ Utils Installation the liblzma ABI, so this option should be used only when it is known to not cause problems. + --enable-external-sha256 + Try to use SHA-256 code from the operating system libc + or similar base system libraries. This doesn't try to + use OpenSSL or libgcrypt or such libraries. + + The reasons to use this option: + + - It makes liblzma slightly smaller. + + - It might improve SHA-256 speed if the implementation + in the operating is very good (but see below). + + External SHA-256 is disabled by default for two reasons: + + - On some operating systems the symbol names of the + SHA-256 functions conflict with OpenSSL's libcrypto. + This causes weird problems such as decompression + errors if an application is linked against both + liblzma and libcrypto. This problem affects at least + FreeBSD 10 and older and MINIX 3.3.0 and older, but + other OSes that provide a function "SHA256_Init" might + also be affected. FreeBSD 11 has the problem fixed. + NetBSD had the problem but it was fixed it in 2009 + already. OpenBSD uses "SHA256Init" and thus never had + a conflict with libcrypto. + + - The SHA-256 code in liblzma is faster than the SHA-256 + code provided by some operating systems. If you are + curious, build two copies of xz (internal and external + SHA-256) and compare the decompression (xz --test) + times: + + dd if=/dev/zero bs=1024k count=1024 \ + | xz -v -0 -Csha256 > foo.xz + time xz --test foo.xz + --disable-xz --disable-xzdec --disable-lzmadec diff --git a/configure.ac b/configure.ac index 32e68efa..7a22bf21 100644 --- a/configure.ac +++ b/configure.ac @@ -275,6 +275,20 @@ m4_foreach([NAME], [SUPPORTED_CHECKS], [AM_CONDITIONAL(COND_CHECK_[]m4_toupper(NAME), test "x$enable_check_[]NAME" = xyes) ])dnl +AC_MSG_CHECKING([if external SHA-256 should be used]) +AC_ARG_ENABLE([external-sha256], AS_HELP_STRING([--enable-external-sha256], + [Use SHA-256 code from the operating system. + See INSTALL for possible subtle problems.]), + [], [enable_external_sha256=no]) +if test "x$enable_check_sha256" != "xyes"; then + enable_external_sha256=no +fi +if test "x$enable_external_sha256" = xyes; then + AC_MSG_RESULT([yes]) +else + AC_MSG_RESULT([no]) +fi + ########################### # Assembler optimizations # @@ -669,48 +683,34 @@ TUKLIB_PHYSMEM TUKLIB_CPUCORES TUKLIB_MBSTR -# Check for system-provided SHA-256. The supported implementations are listed -# below. The detection for the ones marked with [*] has been intentionally -# disabled because they have symbol name conflicts with OpenSSL's libcrypto -# which can cause weird problems (clean namespaces would make things too -# boring, I guess). +# If requsted, check for system-provided SHA-256. At least the following +# implementations are supported: # # OS Headers Library Type Function -# FreeBSD sys/types.h + sha256.h libmd SHA256_CTX SHA256_Init [*] +# FreeBSD sys/types.h + sha256.h libmd SHA256_CTX SHA256_Init # NetBSD sys/types.h + sha2.h SHA256_CTX SHA256_Init # OpenBSD sys/types.h + sha2.h SHA2_CTX SHA256Init # Solaris sys/types.h + sha2.h libmd SHA256_CTX SHA256Init -# MINIX 3 sys/types.h + minix/sha2.h libutil SHA256_CTX SHA256_Init [*] +# MINIX 3 sys/types.h + sha2.h SHA256_CTX SHA256_Init # Darwin CommonCrypto/CommonDigest.h CC_SHA256_CTX CC_SHA256_Init # -# Notes: +# Note that Darwin's CC_SHA256_Update takes buffer size as uint32_t instead +# of size_t. # -# - NetBSD's SHA256_Init doesn't conflict with libcrypto because -# libcrypto on NetBSD was made to use the libc implementation to avoid -# this exact symbol conflict problem: -# http://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2009-012.txt.asc -# -# - As of 2016-03-10, FreeBSD seems to have the issue fixed in SVN head -# but not in the FreeBSD 10 branch. -# -# - Darwin's CC_SHA256_Update takes buffer size as uint32_t instead -# of size_t. -# -# We don't check for e.g. OpenSSL or libgcrypt because we don't want -# to introduce dependencies to other packages by default. Maybe such -# libraries could be supported via additional configure options though. -# -if test "x$enable_check_sha256" = "xyes"; then +sha256_header_found=no +sha256_type_found=no +sha256_func_found=no +if test "x$enable_external_sha256" = "xyes"; then # Test for Common Crypto before others, because Darwin has sha256.h # too and we don't want to use that, because on older versions it # uses OpenSSL functions, whose SHA256_Init is not guaranteed to # succeed. - sha256_header_found=no AC_CHECK_HEADERS( - [CommonCrypto/CommonDigest.h sha256.h sha2.h minix/sha2.h], + [CommonCrypto/CommonDigest.h sha256.h sha2.h], [sha256_header_found=yes ; break]) if test "x$sha256_header_found" = xyes; then - AC_CHECK_TYPES([CC_SHA256_CTX, SHA256_CTX, SHA2_CTX], [], [], + AC_CHECK_TYPES([CC_SHA256_CTX, SHA256_CTX, SHA2_CTX], + [sha256_type_found=yes], [], [[#ifdef HAVE_SYS_TYPES_H # include #endif @@ -722,21 +722,19 @@ if test "x$enable_check_sha256" = "xyes"; then #endif #ifdef HAVE_SHA2_H # include - #endif - #ifdef HAVE_MINIX_SHA2_H - # include #endif]]) - dnl Omit detection of the FreeBSD and MINIX 3 versions: - dnl AC_SEARCH_LIBS([SHA256_Init], [md util]) - AC_SEARCH_LIBS([SHA256Init], [md]) - AC_CHECK_FUNCS([CC_SHA256_Init SHA256_Init SHA256Init], - [break]) + if test "x$sha256_type_found" = xyes ; then + AC_SEARCH_LIBS([SHA256Init], [md]) + AC_SEARCH_LIBS([SHA256_Init], [md]) + AC_CHECK_FUNCS([CC_SHA256_Init SHA256Init SHA256_Init], + [sha256_func_found=yes ; break]) + fi fi fi -AM_CONDITIONAL([COND_INTERNAL_SHA256], - [test "x$ac_cv_func_SHA256_Init" != xyes \ - && test "x$ac_cv_func_SHA256Init" != xyes \ - && test "x$ac_cv_func_CC_SHA256_Init" != xyes]) +AM_CONDITIONAL([COND_INTERNAL_SHA256], [test "x$sha256_func_found" = xno]) +if test "x$enable_external_sha256$sha256_func_found" = xyesno; then + AC_MSG_ERROR([--enable-external-sha256 was specified but no supported external SHA-256 implementation was found]) +fi # Check for SSE2 intrinsics. AC_CHECK_DECL([_mm_movemask_epi8], diff --git a/src/liblzma/check/check.h b/src/liblzma/check/check.h index b8902f05..3007d889 100644 --- a/src/liblzma/check/check.h +++ b/src/liblzma/check/check.h @@ -15,13 +15,12 @@ #include "common.h" -// If either the data type or the function for external SHA-256 is missing, -// use the internal SHA-256 code. -#if !(defined(HAVE_CC_SHA256_CTX) || defined(HAVE_SHA256_CTX) \ - || defined(HAVE_SHA2_CTX)) \ - || !(defined(HAVE_CC_SHA256_INIT) \ - || defined(HAVE_SHA256_INIT) \ - || defined(HAVE_SHA256INIT)) +// If the function for external SHA-256 is missing, use the internal SHA-256 +// code. Due to how configure works, these defines can only get defined when +// both a usable header and a type have already been found. +#if !(defined(HAVE_CC_SHA256_INIT) \ + || defined(HAVE_SHA256_INIT) \ + || defined(HAVE_SHA256INIT)) # define HAVE_INTERNAL_SHA256 1 #endif @@ -35,9 +34,6 @@ #elif defined(HAVE_SHA2_H) # include # include -#elif defined(HAVE_MINIX_SHA2_H) -# include -# include #endif #if defined(HAVE_INTERNAL_SHA256)