linux-kernel - Re: [RFT PATCH 0/3] Fix kfree() of const memory on setting driver

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Message-ID: <afa7001d-901e-55bf-b8dc-77051b1e7f78@canonical.com>
Date:   Tue, 22 Feb 2022 15:06:07 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Abel Vesa <abel.vesa@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [RFT PATCH 0/3] Fix kfree() of const memory on setting
 driver_override

On 22/02/2022 14:51, Rasmus Villemoes wrote:
> On 22/02/2022 14.27, Krzysztof Kozlowski wrote:
>> Hi,
>>
>> Drivers still seem to use driver_override incorrectly. Perhaps my old
>> patch makes sense now?
>> https://lore.kernel.org/all/1550484960-2392-3-git-send-email-krzk@kernel.org/
>>
>> Not tested - please review and test (e.g. by writing to dirver_override
>> sysfs entry with KASAN enabled).
> 
> Perhaps it would make sense to update the core code to release using
> kfree_const(), allowing drivers to set the initial value with
> kstrdup_const(). Drivers that currently use kstrdup() or kasprintf()
> will continue to work [but if they kstrdup() a string literal they could
> be changed to use kstrdup_const].

The core here means several buses, so the change would not be that
small. However I don't see the reason why "driver_override" is special
and should be freed with kfree_const() while most of other places don't
use it.

The driver_override field definition is here obvious: "char *", so any
assignments of "const char *" are logically wrong (although GCC does not
warn of this literal string const discarding). Adding kfree_const() is
hiding the problem - someone did not read the definition of assigned field.

Best regards,
Krzysztof