Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755931Ab0GLO26 (ORCPT ); Mon, 12 Jul 2010 10:28:58 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:49560 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755788Ab0GLO24 (ORCPT ); Mon, 12 Jul 2010 10:28:56 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:subject:message-id:x-mailer:mime-version:content-type :content-transfer-encoding; b=MMPozgnmC+t9EoJbMq1AVGL/WmFYpTfLDzCO9ew7H+yTlvcExuiW8a+CRHXPFr28fd 7qwuNXa5nDlHcQi4jbgcguqEOj6hXH8/f9rX4twdRjf+Ie+8TDOF2Dx6rgTSP+/7JcRI 7PiBixA6zXwu4ATN9fLZbGnc9sF8gPevDXtlU= Date: Mon, 12 Jul 2010 22:29:09 +0800 From: "crosslonelyover" To: "linux-ext4" , "linux-kernel" , "kernel-janitors" Subject: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get Message-ID: <201007122229025316610@gmail.com> X-mailer: Foxmail 6, 15, 201, 22 [cn] Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2002 Lines: 72 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; + down_read(&EXT2_I(inode)->xattr_sem); error = -ENODATA; if (!EXT2_I(inode)->i_file_acl) @@ -181,12 +188,7 @@ bad_block: ext2_error(inode->i_sb, "ext2_xattr_get", error = -EIO; goto cleanup; } - /* find named attribute */ - name_len = strlen(name); - error = -ERANGE; - if (name_len > 255) - goto cleanup; entry = FIRST_ENTRY(bh); while (!IS_LAST_ENTRY(entry)) { struct ext2_xattr_entry *next = -- 1.7.1.1 -- 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/