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Message-ID: <0442526f-b6d9-8868-ac1c-dd11a2d3b2ab@arm.com> Date: Wed, 23 Feb 2022 14:04:23 +0000 From: Robin Murphy <robin.murphy@....com> To: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>, 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 2022-02-22 14:06, Krzysztof Kozlowski wrote: > 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. That's not the issue, though, is it? If I take the struct platform_device definition at face value, this should be perfectly valid: static char foo[] = "foo"; pdev->driver_override = &foo; And in fact that's effectively how the direct assignment form works anyway - string literals are static arrays of type char (or wchar_t), *not* const char, however trying to modify them is undefined behaviour. There's a big difference between "non-const" and "kfree()able", and AFAICS there's no obvious clue that the latter is actually a requirement. Cheers, Robin.
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