[PATCH 5.11 250/601] spi: Fix use-after-free with devm_spi_alloc_*

Greg Kroah-Hartman
2021-05-12T17:22:02Z

From: William A. Kennington III <wak@google.com>

[ Upstream commit 794aaf01444d4e765e2b067cba01cc69c1c68ed9 ]

We can't rely on the contents of the devres list during
spi_unregister_controller(), as the list is already torn down at the
time we perform devres_find() for devm_spi_release_controller. This
causes devices registered with devm_spi_alloc_{master,slave}() to be
mistakenly identified as legacy, non-devm managed devices and have their
reference counters decremented below 0.

------------[ cut here ]------------
WARNING: CPU: 1 PID: 660 at lib/refcount.c:28 refcount_warn_saturate+0x108/0x174
[<b0396f04>] (refcount_warn_saturate) from [<b03c56a4>] (kobject_put+0x90/0x98)
[<b03c5614>] (kobject_put) from [<b0447b4c>] (put_device+0x20/0x24)
r4:b6700140
[<b0447b2c>] (put_device) from [<b07515e8>] (devm_spi_release_controller+0x3c/0x40)
[<b07515ac>] (devm_spi_release_controller) from [<b045343c>] (release_nodes+0x84/0xc4)
r5:b6700180 r4:b6700100
[<b04533b8>] (release_nodes) from [<b0454160>] (devres_release_all+0x5c/0x60)
r8:b1638c54 r7:b117ad94 r6:b1638c10 r5:b117ad94 r4:b163dc10
[<b0454104>] (devres_release_all) from [<b044e41c>] (__device_release_driver+0x144/0x1ec)
r5:b117ad94 r4:b163dc10
[<b044e2d8>] (__device_release_driver) from [<b044f70c>] (device_driver_detach+0x84/0xa0)
r9:00000000 r8:00000000 r7:b117ad94 r6:b163dc54 r5:b1638c10 r4:b163dc10
[<b044f688>] (device_driver_detach) from [<b044d274>] (unbind_store+0xe4/0xf8)

Instead, determine the devm allocation state as a flag on the
controller which is guaranteed to be stable during cleanup.

Fixes: 5e844cc37a5c ("spi: Introduce device-managed SPI controller allocation")
Signed-off-by: William A. Kennington III <wak@google.com>
Link: https://lore.kernel.org/r/20210407095527.2771582-1-wak@google.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/spi/spi.c | 9 ++-------
include/linux/spi/spi.h | 3 +++
2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6f81a3c4c7e0..8131302cd204 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2488,6 +2488,7 @@ struct spi_controller *__devm_spi_alloc_controller(struct device *dev,

ctlr = __spi_alloc_controller(dev, size, slave);
if (ctlr) {
+ ctlr->devm_allocated = true;
*ptr = ctlr;
devres_add(dev, ptr);
} else {
@@ -2834,11 +2835,6 @@ int devm_spi_register_controller(struct device *dev,
}
EXPORT_SYMBOL_GPL(devm_spi_register_controller);

-static int devm_spi_match_controller(struct device *dev, void *res, void *ctlr)
-{
- return *(struct spi_controller **)res == ctlr;
-}
-
static int __unregister(struct device *dev, void *null)
{
spi_unregister_device(to_spi_device(dev));
@@ -2885,8 +2881,7 @@ void spi_unregister_controller(struct spi_controller *ctlr)
/* Release the last reference on the controller if its driver
* has not yet been converted to devm_spi_alloc_master/slave().
*/
- if (!devres_find(ctlr->dev.parent, devm_spi_release_controller,
- devm_spi_match_controller, ctlr))
+ if (!ctlr->devm_allocated)
put_device(&ctlr->dev);

/* free bus id */
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index aa09fdc8042d..f939d8d665d3 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -512,6 +512,9 @@ struct spi_controller {

#define SPI_MASTER_GPIO_SS BIT(5) /* GPIO CS must select slave */

+ /* flag indicating this is a non-devres managed controller */
+ bool devm_allocated;
+
/* flag indicating this is an SPI slave controller */
bool slave;

--
2.30.2