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From: Sergey Shtylyov <s.shtylyov@omprussia.ru>
To: Lukas Wunner <lukas@wunner.de>
Cc: Mark Brown <broonie@kernel.org>, <linux-spi@vger.kernel.org>,
	"Sergei Shtylyov" <sergei.shtylyov@cogentembedded.com>
Subject: Re: [PATCH for-5.10] spi: rpc-if: Fix use-after-free on unbind
Date: Mon, 30 Nov 2020 22:18:12 +0300
Message-ID: <31f68249-2499-7ca6-9804-aad39e94b3b6@omprussia.ru> (raw)
In-Reply-To: <20201129113548.GA2587@wunner.de>

On 11/29/20 2:35 PM, Lukas Wunner wrote:

>>> rpcif_spi_remove() accesses the driver's private data after calling
>>> spi_unregister_controller() even though that function releases the last
>>> reference on the spi_controller and thereby frees the private data.
>>
>> OK, your analysis seems correct (sorry for the delay admitting this :-).
> 
> Thanks!  Is it okay to take this for an Acked-by?

   Not yet. :-)

>> Not sure why spi_unregister_controller() drops the device reference
>> while spi_register_controller() itself doesn't allocate the memory... 
> 
> Yes, that's exactly what I'm trying to move away from with
> devm_spi_alloc_master() (introduced in v5.10-rc5 by 5e844cc37a5c).
> The API as it has been so far has made it really easy to shoot oneself
> in the foot.

   Maybe it needs to be fixed, rather than using the managed device API?

>>> Fix by switching over to the new devm_spi_alloc_master() helper which
>>> keeps the private data accessible until the driver has unbound.
>>
>>    Perhaps the order of the calls in the remove() method could be reversed? 
> 
> I'm not familiar with power management on these Renesas controllers
> but rpcif_disable_rpm() calls pm_runtime_put_sync(), which I assume
> may put the controller to sleep.

   Sigh, that's a stupid typo on my part, being fixed now to pm_runtim_disable()...

> SPI transfers may still be ongoing until spi_unregister_controller()
> returns.  Specifically, this function unbinds and unregisters all
> SPI slaves attached to the controller and the slaves' drivers may
> need to perform SPI transfers to quiesce interrupts on the slaves etc.
> 
> Thus, the correct order is to call spi_unregister_controller() first
> and only then perform further teardown steps.  So the order in
> rpcif_spi_remove() seems correct to me.

   OK. :-)

> The only thing that looks confusing is that rpcif_enable_rpm() calls
> pm_runtime_enable(), whereas rpcif_disable_rpm() calls
> pm_runtime_put_sync().  That looks incongruent.

   Do you need a link to the fix (it a whole patchset of minor fixes)?

> Thanks,
> 
> Lukas

MBR, Sergei

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-16  8:23 [PATCH for-5.10] spi: spi-geni-qcom: " Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: spi-qcom-qspi: " Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: spi-sh: " Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: pxa2xx: " Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: rpc-if: " Lukas Wunner
2020-11-28 20:20   ` Sergey Shtylyov
2020-11-29 11:35     ` Lukas Wunner
2020-11-30 19:18       ` Sergey Shtylyov [this message]
2020-12-02 11:43         ` Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: mxic: Don't leak SPI master in probe error path Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: mt7621: " Lukas Wunner
2020-11-16 11:05   ` Stefan Roese
2020-11-16  8:23 ` [PATCH for-5.10] spi: spi-mtk-nor: " Lukas Wunner
2020-11-17  4:02   ` Ikjoon Jang
2020-11-17 12:32   ` Mark Brown
2020-11-16  8:23 ` [PATCH for-5.10] spi: gpio: " Lukas Wunner
2020-11-16 19:23   ` Andrey Smirnov
2020-11-16 23:03     ` Lukas Wunner
2020-11-16 23:59       ` Andrey Smirnov
2020-11-18  1:08   ` Linus Walleij
2020-11-16  8:23 ` [PATCH for-5.10] spi: npcm-fiu: " Lukas Wunner
2020-11-17 22:38   ` Mark Brown
2020-12-01 13:57   ` Mark Brown
2020-12-01 14:30     ` Lukas Wunner
2020-12-01 17:17       ` Mark Brown
2020-12-01 17:49         ` Lukas Wunner
2020-12-02 15:17           ` Mark Brown
2020-11-16  8:23 ` [PATCH for-5.10] spi: rb4xx: " Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] spi: sc18is602: " Lukas Wunner
2020-11-16  8:23 ` [PATCH for-5.10] media: netup_unidvb: " Lukas Wunner
2020-11-23 14:06   ` Mauro Carvalho Chehab
2020-12-01 13:57   ` Mark Brown

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