linux-kernel - Re: [PATCH 1/3] vfs: dedpue: return s64

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Date:   Mon, 7 May 2018 13:32:09 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [PATCH 1/3] vfs: dedpue: return s64

On Mon, May 7, 2018 at 1:11 PM, Matthew Wilcox <willy@...radead.org> wrote:
> On Mon, May 07, 2018 at 10:21:06AM +0200, Miklos Szeredi wrote:
>> f_op->dedupe_file_range() gets a u64 length to dedup and returns an ssize_t
>> actual length deduped.  This breaks badly on 32bit archs since the returned
>> length will be truncated and possibly overflow into the sign bit (xfs and
>> ocfs2 are affected, btrfs limits actual length to 16MiB).
>>
>> Returning s64 should be good, since clone_verify_area() makes sure that the
>> supplied length doesn't overflow.
>
> Why s64 rather than loff_t?  Particularly since the next patch turns
> the paramters into loff_t.

Next patch turns the offsets into loff_t and leaves "len" as u64.  A
size is definitely not an offset, I'd consider changing the type of
"len" to loff_t a misuse.

Thanks,
Miklos