linux-kernel - Re: [PATCH] /dev/mem: handle out-of-bounds read/write

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Message-ID: <20140130132827.GA22557@kroah.com>
Date:	Thu, 30 Jan 2014 05:28:27 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Petr Tesarik <ptesarik@...e.cz>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] /dev/mem: handle out-of-bounds read/write

On Thu, Jan 30, 2014 at 09:48:02AM +0100, Petr Tesarik wrote:
> The loff_t type may be wider than phys_addr_t (e.g. on 32-bit systems).
> Consequently, the file offset may be truncated in the assignment.
> Currently, /dev/mem wraps around, which may cause applications to read
> or write incorrect regions of memory by accident.

Does that really happen?  If so, that's a userspace bug, right?

> Let's follow POSIX file semantics here and return 0 when reading from
> and -EFBIG when writing to an offset that cannot be represented by a
> phys_addr_t.
> 
> Note that the conditional is optimized out by the compiler if loff_t
> has the same size as phys_addr_t.
> 
> Signed-off-by: Petr Tesarik <ptesarik@...e.cz>
> ---
>  drivers/char/mem.c | 6 ++++++
>  1 file changed, 6 insertions(+)

What is going to break if we apply this patch?  :)

thanks,

greg k-h
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