linux-kernel - Re: [PATCH] dcache: Translating dentry into pathname without taking rename

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Message-ID: <5227E49F.1090809@hp.com>
Date:	Wed, 04 Sep 2013 21:55:43 -0400
From:	Waiman Long <waiman.long@...com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH] dcache: Translating dentry into pathname without taking
 rename_lock

On 09/04/2013 03:43 PM, Al Viro wrote:
> On Wed, Sep 04, 2013 at 03:33:00PM -0400, Waiman Long wrote:
>
>> I have thought about that. But if a d_move() is going on, the string
>> in the buffer will be discarded as the sequence number will change.
>> So whether or not it have embedded null byte shouldn't matter. That
>> is why I didn't add code to do byte-by-byte copy at this first
>> patch. I can add code to do that if you think it is safer to do so.
> Sigh...  Junk in the output is not an issue; reading from invalid address
> is, since you might not survive to the sequence number check.  Again,
> if p is an address returned by kmalloc(size, ...), dereferencing p + offset
> is not safe unless offset is less than size.

Yeah, I understand that. As said in my reply to Linus, I will use 
memchr() to see if there is null byte within the specified length. If 
one is found, I will assume the string is not valid and return error to 
the caller.

Longman
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