[v1] spi: Fix null dereference on suspend

Commit Message

Mark Hasemeyer Nov. 7, 2023, 9:47 p.m. UTC

A race condition exists where a synchronous (noqueue) transfer can be
active during a system suspend. This can cause a null pointer
dereference exception to occur when the system resumes.

Example order of events leading to the exception:
1. spi_sync() calls __spi_transfer_message_noqueue() which sets
   ctlr->cur_msg
2. Spi transfer begins via spi_transfer_one_message()
3. System is suspended interrupting the transfer context
4. System is resumed
6. spi_controller_resume() calls spi_start_queue() which resets cur_msg
   to NULL
7. Spi transfer context resumes and spi_finalize_current_message() is
   called which dereferences cur_msg (which is now NULL)

Wait for synchronous transfers to complete before suspending by
acquiring the bus mutex and setting/checking a suspend flag.

Signed-off-by: Mark Hasemeyer <[e-mail]>
---

 drivers/spi/spi.c       | 56 ++++++++++++++++++++++++++++-------------
 include/linux/spi/spi.h |  1 +
 2 files changed, 40 insertions(+), 17 deletions(-)

Comments

Mark Brown Nov. 8, 2023, 5:34 p.m. UTC | #1

On Tue, 07 Nov 2023 14:47:43 -0700, Mark Hasemeyer wrote:
> A race condition exists where a synchronous (noqueue) transfer can be
> active during a system suspend. This can cause a null pointer
> dereference exception to occur when the system resumes.
> 
> Example order of events leading to the exception:
> 1. spi_sync() calls __spi_transfer_message_noqueue() which sets
>    ctlr->cur_msg
> 2. Spi transfer begins via spi_transfer_one_message()
> 3. System is suspended interrupting the transfer context
> 4. System is resumed
> 6. spi_controller_resume() calls spi_start_queue() which resets cur_msg
>    to NULL
> 7. Spi transfer context resumes and spi_finalize_current_message() is
>    called which dereferences cur_msg (which is now NULL)
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: Fix null dereference on suspend
      commit: 4f646616d11c3ec3f5a5cb2cd683cfc0fa9a5018

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

Patch

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 791df0e69105..8ead7acb99f3 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3317,33 +3317,52 @@  void spi_unregister_controller(struct spi_controller *ctlr)
 }
 EXPORT_SYMBOL_GPL(spi_unregister_controller);
 
+static inline int __spi_check_suspended(const struct spi_controller *ctlr)
+{
+	return ctlr->flags & SPI_CONTROLLER_SUSPENDED ? -ESHUTDOWN : 0;
+}
+
+static inline void __spi_mark_suspended(struct spi_controller *ctlr)
+{
+	mutex_lock(&ctlr->bus_lock_mutex);
+	ctlr->flags |= SPI_CONTROLLER_SUSPENDED;
+	mutex_unlock(&ctlr->bus_lock_mutex);
+}
+
+static inline void __spi_mark_resumed(struct spi_controller *ctlr)
+{
+	mutex_lock(&ctlr->bus_lock_mutex);
+	ctlr->flags &= ~SPI_CONTROLLER_SUSPENDED;
+	mutex_unlock(&ctlr->bus_lock_mutex);
+}
+
 int spi_controller_suspend(struct spi_controller *ctlr)
 {
-	int ret;
+	int ret = 0;
 
 	/* Basically no-ops for non-queued controllers */
-	if (!ctlr->queued)
-		return 0;
-
-	ret = spi_stop_queue(ctlr);
-	if (ret)
-		dev_err(&ctlr->dev, "queue stop failed\n");
+	if (ctlr->queued) {
+		ret = spi_stop_queue(ctlr);
+		if (ret)
+			dev_err(&ctlr->dev, "queue stop failed\n");
+	}
 
+	__spi_mark_suspended(ctlr);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(spi_controller_suspend);
 
 int spi_controller_resume(struct spi_controller *ctlr)
 {
-	int ret;
-
-	if (!ctlr->queued)
-		return 0;
+	int ret = 0;
 
-	ret = spi_start_queue(ctlr);
-	if (ret)
-		dev_err(&ctlr->dev, "queue restart failed\n");
+	__spi_mark_resumed(ctlr);
 
+	if (ctlr->queued) {
+		ret = spi_start_queue(ctlr);
+		if (ret)
+			dev_err(&ctlr->dev, "queue restart failed\n");
+	}
 	return ret;
 }
 EXPORT_SYMBOL_GPL(spi_controller_resume);
@@ -4147,8 +4166,7 @@  static void __spi_transfer_message_noqueue(struct spi_controller *ctlr, struct s
 	ctlr->cur_msg = msg;
 	ret = __spi_pump_transfer_message(ctlr, msg, was_busy);
 	if (ret)
-		goto out;
-
+		dev_err(&ctlr->dev, "noqueue transfer failed\n");
 	ctlr->cur_msg = NULL;
 	ctlr->fallback = false;
 
@@ -4164,7 +4182,6 @@  static void __spi_transfer_message_noqueue(struct spi_controller *ctlr, struct s
 		spi_idle_runtime_pm(ctlr);
 	}
 
-out:
 	mutex_unlock(&ctlr->io_mutex);
 }
 
@@ -4187,6 +4204,11 @@  static int __spi_sync(struct spi_device *spi, struct spi_message *message)
 	int status;
 	struct spi_controller *ctlr = spi->controller;
 
+	if (__spi_check_suspended(ctlr)) {
+		dev_warn_once(&spi->dev, "Attempted to sync while suspend\n");
+		return -ESHUTDOWN;
+	}
+
 	status = __spi_validate(spi, message);
 	if (status != 0)
 		return status;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 86825c88b576..255a0562aea5 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -566,6 +566,7 @@  struct spi_controller {
 #define SPI_CONTROLLER_MUST_RX		BIT(3)	/* Requires rx */
 #define SPI_CONTROLLER_MUST_TX		BIT(4)	/* Requires tx */
 #define SPI_CONTROLLER_GPIO_SS		BIT(5)	/* GPIO CS must select slave */
+#define SPI_CONTROLLER_SUSPENDED	BIT(6)	/* Currently suspended */
 
 	/* Flag indicating if the allocation of this struct is devres-managed */
 	bool			devm_allocated;