Re: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing negative f_pos

From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Christoph Hellwig <hch@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Eric Paris <eparis@redhat.com>, Nick Piggin <npiggin@suse.de>,
	Andi Kleen <andi@firstfloor.org>,
	David Howells <dhowells@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>, <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing negative f_pos
Date: Sat, 16 Jan 2010 21:54:39 +0900	[thread overview]
Message-ID: <87bpgurz00.fsf@devron.myhome.or.jp> (raw)
In-Reply-To: <20100115014422.959401729@intel.com> (Wu Fengguang's message of "Fri, 15 Jan 2010 09:40:00 +0800")

Wu Fengguang <fengguang.wu@intel.com> writes:

> +static int
> +__negative_fpos_check(struct file *file, loff_t pos, size_t count)
> +{
> +	/*
> +	 * pos or pos+count is negative here, check overflow.
> +	 * too big "count" will be caught in rw_verify_area().
> +	 */
> +	if ((pos < 0) && (pos + count < pos))
> +		return -EOVERFLOW;
> +	if (file->f_mode & FMODE_NEG_OFFSET)
> +		return 0;
> +	return -EINVAL;
> +}
> +
>  /*
>   * rw_verify_area doesn't like huge counts. We limit
>   * them to something that fits in "int" so that others
> @@ -222,8 +236,11 @@ int rw_verify_area(int read_write, struc
>  	if (unlikely((ssize_t) count < 0))
>  		return retval;
>  	pos = *ppos;
> -	if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
> -		return retval;
> +	if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) {
> +		retval = __negative_fpos_check(file, pos, count);
> +		if (retval)
> +			return retval;
> +	}
>  
>  	if (unlikely(inode->i_flock && mandatory_lock(inode))) {
>  		retval = locks_mandatory_area(

Um... How do lseek() work? It sounds like to violate error code range.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>