Dear Greg, Dear Sasha,

please consider applying the patch below to v4.4-stable.

It is a backport of upstream commit 794aaf01444d, which has already been applied to all stable kernels going back to v4.14.

Thanks!

Lukas

-- >8 --

From 429a36a750568599640ae8b9e603d639181fee9a Mon Sep 17 00:00:00 2001

From: "William A. Kennington III" wak@google.com Date: Wed, 7 Apr 2021 02:55:27 -0700 Subject: [PATCH] spi: Fix use-after-free with devm_spi_alloc_*

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 --- 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 e85feee750e3..f743b95d5171 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -1762,6 +1762,7 @@ struct spi_master *devm_spi_alloc_master(struct device *dev, unsigned int size)

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 device *dev, struct spi_master *master) } 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_master *master) /* 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)) diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index f5d387140c46..da487e905337 100644 --- 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;