From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933173AbcBPWtn (ORCPT ); Tue, 16 Feb 2016 17:49:43 -0500 Received: from mail-wm0-f49.google.com ([74.125.82.49]:36895 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932573AbcBPWtk (ORCPT ); Tue, 16 Feb 2016 17:49:40 -0500 From: Rasmus Villemoes To: Alexander Viro , Jeff Layton , "J. Bruce Fields" Cc: Rasmus Villemoes , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] vfs: make sure struct filename->iname is word-aligned Date: Tue, 16 Feb 2016 23:49:24 +0100 Message-Id: <1455662966-7977-1-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I noticed that offsetof(struct filename, iname) is actually 28 on 64 bit platforms, so we always pass an unaligned pointer to strncpy_from_user. This is mostly a problem for those 64 bit platforms without HAVE_EFFICIENT_UNALIGNED_ACCESS, but even on x86_64, unaligned accesses carry a penalty, especially when done in a loop. Let's try to ensure we always pass an aligned destination pointer to strncpy_from_user. I considered making refcnt a long instead of doing the union thing, and mostly ended up tossing a coin. Signed-off-by: Rasmus Villemoes --- Cc'ing Linus, not because it's urgent in any way, but because he's usually interested in strncpy_from_user and he can probably tell me why this is completely immaterial. fs/namei.c | 2 ++ include/linux/fs.h | 5 ++++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/namei.c b/fs/namei.c index f624d132e01e..bd150fa799a2 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -35,6 +35,7 @@ #include #include #include +#include #include #include "internal.h" @@ -127,6 +128,7 @@ getname_flags(const char __user *filename, int flags, int *empty) struct filename *result; char *kname; int len; + BUILD_BUG_ON(offsetof(struct filename, iname) % sizeof(long) != 0); result = audit_reusename(filename); if (result) diff --git a/include/linux/fs.h b/include/linux/fs.h index ae681002100a..d522e6391855 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2245,7 +2245,10 @@ struct filename { const char *name; /* pointer to actual string */ const __user char *uptr; /* original userland pointer */ struct audit_names *aname; - int refcnt; + union { + int refcnt; + long __padding; + }; const char iname[]; }; -- 2.1.4