Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754411Ab0GWIia (ORCPT ); Fri, 23 Jul 2010 04:38:30 -0400 Received: from cantor.suse.de ([195.135.220.2]:55293 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752090Ab0GWIi1 (ORCPT ); Fri, 23 Jul 2010 04:38:27 -0400 Date: Fri, 23 Jul 2010 10:37:59 +0200 From: Jan Kara To: shenghui Cc: Jan Kara , linux-ext4 , linux-kernel , kernel-janitors Subject: Re: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get Message-ID: <20100723083759.GA3305@quack.suse.cz> References: <201007122229025316610@gmail.com> <20100721174457.GE1215@atrey.karlin.mff.cuni.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2444 Lines: 65 On Thu 22-07-10 08:03:18, shenghui wrote: > 2010/7/22 Jan Kara : > >> Hi, > >> ? ? ? ?I walked through ext2_xattr_get, and felt that we can > >> do some optimization on it. For name_len check, it's done > >> after down xattr_sem and sb_read, both of which are time > >> consuming operation compared with strlen: > >> ? ? ? ? ?down_read(&EXT2_I(inode)->xattr_sem); > >> ?... > >> ? ? ? ? ?bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl); > >> ?... > >> ? ? ? ? ?/* find named attribute */ > >> ? ? ? ? ?name_len = strlen(name); > >> > >> ? ? ? ? ?error = -ERANGE; > >> ? ? ? ? ?if (name_len > 255) > >> ? ? ? ? ? ? ? ? ?goto cleanup; > >> > >> ? ? ? ?Most of the case, you'll get one valid block, but if the > >> name len > 255, then the xattr_sem down and sb_bread operation > >> can be seen as a waste of time. So I think we'd better do > >> name len check as early as possible. > >> ? ? ? ?Following is my patch, and it's against 2.6.35-rc4. > >> Please check it. > >> > >> Signed-off-by: Wang Sheng-Hui > >> --- > >> ?fs/ext2/xattr.c | ? 12 +++++++----- > >> ?1 files changed, 7 insertions(+), 5 deletions(-) > >> > >> diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c > >> index 7c39157..0b94d61 100644 > >> --- a/fs/ext2/xattr.c > >> +++ b/fs/ext2/xattr.c > >> @@ -161,6 +161,13 @@ ext2_xattr_get(struct inode *inode, int name_index, const char *name, > >> > >> ? ? ? if (name == NULL) > >> ? ? ? ? ? ? ? return -EINVAL; > >> + > >> + ? ? /* find named attribute */ > >> + ? ? name_len = strlen(name); > >> + ? ? error = -ERANGE; > >> + ? ? if (name_len > 255) > >> + ? ? ? ? ? ? goto cleanup; > > ?But you cannot go to cleanup here because you don't hold xattr_sem... > > > > Sorry, I'm a little confused by your words. > The patch just checks name_len, and it > doesn't need xattr_sem. Checking of name_len is fine as you did it. But I wanted to point out that if name_len is greater than 255, you then go to 'cleanup' label which tries to do up_read(&EXT2_I(inode)->xattr_sem). But that's a bug because after you moved the code, we don't hold xattr_sem at the moment we check name_len. Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/