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    Subject[PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get
    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 =
    --
    1.7.1.1







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