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Date: Tue, 18 Dec 2012 22:02:23 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, Ming Lei <ming.lei@canonical.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v2] firmware: make sure paths remain relative
Message-ID: <20121218220223.5ae69bf0@pyramind.ukuu.org.uk>
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On Tue, 18 Dec 2012 13:04:49 -0800
Kees Cook <keescook@chromium.org> wrote:

> Some devices have configurable firmware locations. If these configuration
> mechanisms are exposed to unprivileged userspace, it may be possible to
> load firmware from an unexpected location. To minimize the risk of this,
> make sure the string "../" does not appear in the firmware name. This
> means that neither the users of request_firmware, nor the uevent handler
> have to do this filtering themselves.

Have you verified no existing distribution ever does this ?


> +	if (strstr(name, "../")) {

and this is obviously buggy and hasn't been tested

Hint foo/bar../baz

You need to check for ^../ /../ and /..$

Alan