Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759188Ab0GVADW (ORCPT ); Wed, 21 Jul 2010 20:03:22 -0400 Received: from mail-gy0-f174.google.com ([209.85.160.174]:55122 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759120Ab0GVADU convert rfc822-to-8bit (ORCPT ); Wed, 21 Jul 2010 20:03:20 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=ncwY/b2oBZ45LA0j3Tf2xAmKYcTnwHS5WIdJtb5lqGGCF5EY+d5Q/Jad3VBVCKV2AT VIlDVMRCDuFeUt7KxomxRLqReQyzZAcf7rPesyFpdUZYVLN9maeHMEXfgPI1Qq1a2wmc xhuWI4norJMbTkySTjas2MsxU+AeYUwwvIoqc= MIME-Version: 1.0 In-Reply-To: <20100721174457.GE1215@atrey.karlin.mff.cuni.cz> References: <201007122229025316610@gmail.com> <20100721174457.GE1215@atrey.karlin.mff.cuni.cz> Date: Thu, 22 Jul 2010 08:03:18 +0800 Message-ID: Subject: Re: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get From: shenghui To: Jan Kara Cc: linux-ext4 , linux-kernel , kernel-janitors Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2068 Lines: 62 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. -- Thanks and Best Regards, shenghui -- 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/