linux-ext4 - Re: [PATCH] ext4: avoid unneeded lookup when xattr name is invalid

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Message-ID: <20140512140044.GC31376@thunk.org>
Date:	Mon, 12 May 2014 10:00:44 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Zhang Zhen <zhenzhang.zhang@...wei.com>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: avoid unneeded lookup when xattr name is invalid

On Fri, Apr 11, 2014 at 03:15:07PM +0800, Zhang Zhen wrote:
> In ext4_xattr_set_handle() we have checked the xattr name's length. So we should
> also check it in ext4_xattr_get() to avoid unneeded lookup caused by invalid name.
> 
> Signed-off-by: Zhang Zhen <zhenzhang.zhang@...wei.com>

Applied, although I dropped this bit:

> In addition, we deleted the check of NULL in ext4_xattr_set_handle(), because in all
> the callers of the ext4_xattr_set_handle(), the name can't be NULL.

Verifying this is non-trivial, since there are many non-local
users of this function, and in order to make sure this is true you
need to verify (at least) the callers of the callers.  I could be
convinced to turn this into a BUG_ON(!name), or "if
(unlikely(!name))", but leaving the check in is a good idea, since
even if it is true today, it's not necessarily guarantted to be true N
years in the future.

					- Ted
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