linux-kernel - Re: [patch] md: bitmap read

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Date:	Wed, 24 Jan 2007 13:39:59 +1100
From:	Neil Brown <neilb@...e.de>
To:	"yang yin" <yinyang801120@...il.com>
Cc:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] md: bitmap read_page error

On Tuesday January 23, yinyang801120@...il.com wrote:
> I think your patch is not enough to slove the read_page error
> completely. I think in the bitmap_init_from_disk we also need to check
> the 'count' never exceeds the size of file before calling the
> read_page function. How do your think about it.
> Thanks your reply.

bitmap_init_from_disk already has a test:

	if (file && i_size_read(file->f_mapping->host) < bytes + sizeof(bitmap_super_t)) {
		printk(KERN_INFO "%s: bitmap file too short %lu < %lu\n",
			bmname(bitmap),
			(unsigned long) i_size_read(file->f_mapping->host),
			bytes + sizeof(bitmap_super_t));
		goto out;
	}

so 'bytes' of the bitmap must fit entirely within the file, and count
is set:
			if (index == num_pages-1)
				count = bytes + sizeof(bitmap_super_t)
					- index * PAGE_SIZE;
			else
				count = PAGE_SIZE;
which ensures that it will not go beyond the end of the file.

So I don't think count can ever exceed the size of the file in this
case. 

Can you still see a problem?

Thanks,
NeilBrown
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