linux-kernel - Re: [PATCH] block: create ioctl to discard-or-zeroout a range of blocks

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Date:	Tue, 10 Nov 2015 22:14:35 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	"Seymour, Shane M" <shane.seymour@....com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: Re: [PATCH] block: create ioctl to discard-or-zeroout a range of
 blocks

On Wed, Nov 11, 2015 at 05:30:07AM +0000, Seymour, Shane M wrote:
> A quick question about this part of the patch:
> 
> > +	uint64_t end = start + len - 1;
> 
> > +	if (end >= i_size_read(bdev->bd_inode))
>  		return -EINVAL;
>  
> > +	/* Invalidate the page cache, including dirty pages */
> > +	mapping = bdev->bd_inode->i_mapping;
> > +	truncate_inode_pages_range(mapping, start, end);
> 
> blk_ioctl_zeroout accepts unsigned values for start and end (uint64_t) but
> loff_t types are turned from i_size_read() and passed as the 2nd and 3rd
> values to truncate_inode_pages_range() and loff_t is a signed value. It
> should be possible to pass in some values would overflow the calculation of
> end causing the test on the value of end and the result of i_size_read to
> pass but then end up passing a large unsigned value for in start that would
> be implicitly converted to signed in truncate_inode_pages_range. I was
> wondering if you'd tested passing in data that would cause sign conversion
> issues when passed into truncate_inode_pages_range (does it handle it
> gracefully?) or should this code:
> 
> 	if (start & 511)
>  		return -EINVAL;
>  	if (len & 511)
>  		return -EINVAL;
> 
> be something more like this (for better sanity checking of your arguments)
> which will ensure that you don't have implicit conversion issues from
> unsigned to signed and ensure that the result of adding them together won't
> either:
> 
> 	if ((start & 511) || (start > (uint64_t)LLONG_MAX))
>  		return -EINVAL;
>  	if ((len & 511) ) || (len > (uint64_t)LLONG_MAX))
>  		return -EINVAL;
> 	if (end > (uint64_t)LLONG_MAX)
> 		return -EINVAL;
> 
> My apologies in advance if I've made a mistake when looking at this and my
> concerns about unsigned values being implicitly converted to signed are
> unfounded (I would have hoped for compiler warnings about any implicit
> conversions though).

I don't have a device large enough to test for signedness errors, since passing
huge values for start and len never make it past the i_size_read check.
However, I do see that I forgot to check the padding values, so I'll update
that.

--D
> 
> Thanks
> Shane
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