Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20181101131250.41636-1-smuchun@gmail.com> <CACRpkdaURruTj6W=ozXpKEvLpxLa=6tLdDywac1uj61Hg8ZKpA@mail.gmail.com>
In-Reply-To: <CACRpkdaURruTj6W=ozXpKEvLpxLa=6tLdDywac1uj61Hg8ZKpA@mail.gmail.com>
From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Fri, 2 Nov 2018 10:24:53 +0100
Message-ID: <CACRpkdZ_jrNNB7n0DOuL6n_JtupiwacbMxWcockTak9F8fdAjA@mail.gmail.com>
Subject: Re: [PATCH v2] gpiolib: Fix possible use after free on label
To:     smuchun@gmail.com, Nicolas Pitre <nico@linaro.org>
Cc:     Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Nov 1, 2018 at 4:27 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> On Thu, Nov 1, 2018 at 2:13 PM Muchun Song <smuchun@gmail.com> wrote:
>
> > gpiod_request_commit() copies the pointer to the label passed as
> > an argument only to be used later. But there's a chance the caller
> > could immediately free the passed string(e.g., local variable).
> > This could trigger a use after free when we use gpio label(e.g.,
> > gpiochip_unlock_as_irq(), gpiochip_is_requested()).
> >
> > To be on the safe side: duplicate the string with kstrdup_const()
> > so that if an unaware user passes an address to a stack-allocated
> > buffer, we won't get the arbitrary label.
> >
> > Also fix gpiod_set_consumer_name().
> >
> > Signed-off-by: Muchun Song <smuchun@gmail.com>
>
> I am still a bit worried about the kstrdup_const() that this
> introduces.

Forget it. I realized after actually reading the code
for kstrdup_const() that it really does exactly
what we want.

I should stop assuming things are syntactic sugar
in the kernel, we have some really smart people
working with it...

Patch applied.

Yours,
Linus Walleij