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SubjectRe: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get
  于 2010-7-12 22:29, crosslonelyover 写道:
> 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<crosslonelyover@gmail.com>
> ---
> 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 =
Hi, I noticed in ext2_xattr_set, name_len check is done
before
down_write(&EXT2_I(inode)->xattr_sem);
So I think ext2_xattr_get should do in the same way.

Please check this patch.

--
Thanks and Regards,
shenghui

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