[PATCH 4.4 20/54] spi: Fix use-after-free with devm_spi_alloc_*

Greg Kroah-Hartman
2021-05-31T13:17:28Z

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

commit 794aaf01444d4e765e2b067cba01cc69c1c68ed9 upstream.

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>
[lukas: backport to v4.4.270]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/spi/spi.c | 9 ++-------
include/linux/spi/spi.h | 3 +++
2 files changed, 5 insertions(+), 7 deletions(-)

--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1762,6 +1762,7 @@ struct spi_master *devm_spi_alloc_master

master = spi_alloc_master(dev, size);
if (master) {
+ master->devm_allocated = true;
*ptr = master;
devres_add(dev, ptr);
} else {
@@ -1951,11 +1952,6 @@ int devm_spi_register_master(struct devi
}
EXPORT_SYMBOL_GPL(devm_spi_register_master);

-static int devm_spi_match_master(struct device *dev, void *res, void *master)
-{
- return *(struct spi_master **)res == master;
-}
-
static int __unregister(struct device *dev, void *null)
{
spi_unregister_device(to_spi_device(dev));
@@ -1994,8 +1990,7 @@ void spi_unregister_master(struct spi_ma
/* Release the last reference on the master if its driver
* has not yet been converted to devm_spi_alloc_master().
*/
- if (!devres_find(master->dev.parent, devm_spi_release_master,
- devm_spi_match_master, master))
+ if (!master->devm_allocated)
put_device(&master->dev);

if (IS_ENABLED(CONFIG_SPI_DYNAMIC))
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -425,6 +425,9 @@ struct spi_master {
#define SPI_MASTER_MUST_RX BIT(3) /* requires rx */
#define SPI_MASTER_MUST_TX BIT(4) /* requires tx */

+ /* flag indicating this is a non-devres managed controller */
+ bool devm_allocated;
+
/* lock and mutex for SPI bus locking */
spinlock_t bus_lock_spinlock;
struct mutex bus_lock_mutex;