linux-kernel - Re: [PATCH] compat: fix possible out-of-bound accesses in compat_get_bitmap() and compat_put

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Date:	Sat, 6 Jun 2015 09:13:46 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Helge Deller <deller@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] compat: fix possible out-of-bound accesses in
 compat_get_bitmap() and compat_put_bitmap()

On Fri, Jun 5, 2015 at 11:24 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Yes, but... if we decrement that sucker at all, why do we need to play with
> i at all?  We need exactly nr_compat_longs get_user(), so why not make _that_
> the condition in the single-level loop?

Yeah, I think that code could be clarified further, no argument there.

And wee could just do it the copy in compat_long_t directly on
little-endian and get rid of the complications entirely, but then we'd
have the worry of separate code for big-endian, so I guess that's not
worth it (it's not like this should be hugely performance-sensitive).

I think most of that code falls under "don't touch it if it ain't
broke", with the corollary being "touch it as little as possible even
when it is broke"

                Linus
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