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: <1212681477.3953.154.camel@calx>
Date:	Thu, 05 Jun 2008 10:57:57 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Thomas Tuttle <ttuttle@...gle.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, 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.

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.

-- 
Mathematics is the supreme nostalgia of our time.

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