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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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