From: Lukas Wunner <lukas@wunner.de>
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-spi <linux-spi@vger.kernel.org>,
Mark Brown <broonie@kernel.org>
Subject: Re: Use after free in bcm2835_spi_remove()
Date: Wed, 14 Oct 2020 16:09:12 +0200 [thread overview]
Message-ID: <20201014140912.GB24850@wunner.de> (raw)
In-Reply-To: <bd6eaa71-46cc-0aca-65ff-ae716864cbe3@gmail.com>
On Tue, Oct 13, 2020 at 04:48:42PM -0700, Florian Fainelli wrote:
> With KASAN now working on ARM 32-bit, I was able to get the following
> trace upon reboot which invokes bcm2835_spi_shutdown() calling
> bcm2835_spi_remove(), the same can be triggered by doing a driver unbind:
Thank you for the report. Apparently the problem is that
spi_unregister_controller() drops the last ref on the controller,
causing it to be freed, and afterwards we access the controller's
private data, which is part of the same allocation as
struct spi_controller:
bcm2835_spi_remove()
spi_unregister_controller()
device_unregister()
put_device()
spi_controller_release() # spi_master_class.dev_release()
kfree(ctlr)
bcm2835_dma_release(ctlr, bs)
...
However, when I submitted commit 9dd277ff92d0, I double-checked that
the kfree() happens after bcm2835_spi_remove() has finished and I
even wrote in the commit message:
"Note that
the struct spi_controller as well as the driver-private data are not
freed until after bcm2835_spi_remove() has finished, so accessing them
is safe."
I'm puzzled now that it doesn't work as intended. I do not see any
recent commits which changed the behavior, so I must have made a
mistake and missed something.
The below patch should fix the issue. Could you verify that?
Unfortunately I do not have access to a RasPi currently.
An alternative to this patch would be a devm function which acquires
a ref on the spi controller on ->probe() and automatically releases it
after ->remove() has finished. This could be used by other SPI drivers
as well.
Thanks,
Lukas
-- >8 --
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index 41986ac..5254fda 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -1377,6 +1377,7 @@ static int bcm2835_spi_remove(struct platform_device *pdev)
bcm2835_debugfs_remove(bs);
+ spi_controller_get(ctlr);
spi_unregister_controller(ctlr);
bcm2835_dma_release(ctlr, bs);
@@ -1386,6 +1387,7 @@ static int bcm2835_spi_remove(struct platform_device *pdev)
BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX);
clk_disable_unprepare(bs->clk);
+ spi_controller_put(ctlr);
return 0;
}
next prev parent reply other threads:[~2020-10-14 14:18 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-13 23:48 Use after free in bcm2835_spi_remove() Florian Fainelli
2020-10-14 14:09 ` Lukas Wunner [this message]
2020-10-14 19:40 ` Vladimir Oltean
2020-10-14 20:25 ` Mark Brown
2020-10-14 21:20 ` Florian Fainelli
2020-10-22 12:12 ` Lukas Wunner
2020-10-15 5:38 ` Lukas Wunner
2020-10-15 12:53 ` Mark Brown
2020-10-28 9:59 ` Lukas Wunner
2020-10-29 22:24 ` Mark Brown
2020-11-11 19:07 ` [PATCH 0/4] Use-after-free be gone Lukas Wunner
2020-11-11 19:07 ` [PATCH 1/4] spi: Introduce device-managed SPI controller allocation Lukas Wunner
2020-11-11 19:07 ` [PATCH 2/4] spi: bcm2835: Fix use-after-free on unbind Lukas Wunner
2020-11-11 20:18 ` Florian Fainelli
2020-11-11 19:07 ` [PATCH 3/4] spi: bcm2835aux: " Lukas Wunner
2020-11-11 19:07 ` [PATCH 4/4] spi: bcm-qspi: " Lukas Wunner
2020-11-11 21:12 ` Florian Fainelli
2020-11-12 13:50 ` [PATCH 0/4] Use-after-free be gone Mark Brown
2020-11-12 19:39 ` Mark Brown
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