linux-kernel - Re: [PATCH 1/5] pagemap: Modify add_to_pagemap to use copy_to_user instead of put

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Message-ID: <4ca0a85e0806050901q52deba94r3056fdb0e7d46c8c@mail.gmail.com>
Date:	Thu, 5 Jun 2008 12:01:06 -0400
From:	"Thomas Tuttle" <ttuttle@...gle.com>
To:	"Matt Mackall" <mpm@...enic.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] pagemap: Modify add_to_pagemap to use copy_to_user instead of put_user.

On Thu, Jun 5, 2008 at 11:57 AM, Matt Mackall <mpm@...enic.com> wrote:
>
> On Thu, 2008-06-05 at 11:04 -0400, Thomas Tuttle wrote:
>> While fiddling with pagemap, I discovered a bug in add_to_pagemap.
>> When it is copying an entry that is not at the end of the buffer, it
>> uses put_user to copy a u64 into a char* buffer.  The problem is that
>> put_user determines how much to copy based on the size of the
>> *destination*, not the source, so it only copied one byte.  To fix
>> this, I replaced the call to put_user with a call to copy_to_user, as
>> is used when copying the last (possibly partial) PFN into the buffer.0
>
> This looks fine to me, so:
>
> Acked-by: Matt Mackall <mpm@...enic.com>
>
> But your 3/5 undoes this, right? So we should just take one or the other
> route. While I like going the simplifying route, it's not very pretty
> from the user interface point of view. But it does have plenty of
> precedent in direct-I/O-like things.

No, my 3/5 further keeps the use of copy_to_user instead of put_user,
but eliminates entirely the code for partial reads.  3/5 depends on
1/5.

--ttuttle
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