[PATCH] spi: fix use-after-free on managed registration failure

[Johan Hovold <johan@kernel.org>]

The SPI API is asymmetric and the controller is freed as part of
deregistration (unless it has been allocated using
devm_spi_alloc_host/target()).

A recent change converting the managed registration function to use
devm_add_action_or_reset() inadvertently introduced a (mostly
theoretical) regression where a non-devres managed controller could be
freed as part of failed registration. This in turn would lead to
use-after-free in controller driver error paths.

Fix this by taking another reference before calling
devm_add_action_or_reset() and not releasing it on errors for
non-devres allocated controllers.

An alternative would be a partial revert of the offending commit, but
it is better to handle this explicitly until the API has been fixed
(e.g. see 5e844cc37a5c ("spi: Introduce device-managed SPI controller
allocation")).

Fixes: b6376dbed8e1 ("spi: Simplify devm_spi_*_controller()")
Reported-by: Felix Gu <ustc.gu@gmail.com>
Link: https://lore.kernel.org/all/20260324145548.139952-1-ustc.gu@gmail.com/
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/spi/spi.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index cb00619864cf..aac378e668a8 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3537,8 +3537,19 @@ int devm_spi_register_controller(struct device *dev,
 	if (ret)
 		return ret;
 
-	return devm_add_action_or_reset(dev, devm_spi_unregister_controller, ctlr);
+	/*
+	 * Prevent controller from being freed by spi_unregister_controller()
+	 * if devm_add_action_or_reset() fails for a non-devres allocated
+	 * controller.
+	 */
+	spi_controller_get(ctlr);
+
+	ret = devm_add_action_or_reset(dev, devm_spi_unregister_controller, ctlr);
 
+	if (ret == 0 || ctlr->devm_allocated)
+		spi_controller_put(ctlr);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(devm_spi_register_controller);
 
-- 
2.52.0