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SubjectRe: [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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