From: "crosslonelyover" Subject: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get Date: Mon, 12 Jul 2010 22:29:09 +0800 Message-ID: <201007122229025316610@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "linux-ext4" , "linux-kernel" , "kernel-janitors" Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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