Re: [PATCH] check name_len before down_read xattr_sem and sb_read in ext2_xattr_get

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 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@xxxxxxxxx>
---
  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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