Since it's not currently safe to take device_lock() in the IOMMU probe
path, that can race against really_probe() setting dev->driver before
attempting to bind. The race itself isn't so bad, since we're only
concerned with dereferencing dev->driver itself anyway, but sadly my
attempt to implement the check with minimal churn leads to a kind of
TOCTOU issue, where dev->driver becomes valid after to_fsl_mc_driver(NULL)
is already computed, and thus the check fails to work as intended.
Will and I both hit this with the platform bus, but the pattern here is
the same, so fix it for correctness too.
Reported-by: Will McVicker <willmcvic...@google.com>
Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
Signed-off-by: Robin Murphy <robin.mur...@arm.com>
---
drivers/bus/fsl-mc/fsl-mc-bus.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
index a8be8cf246fb..67031136ef66 100644
--- a/drivers/bus/fsl-mc/fsl-mc-bus.c
+++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
@@ -139,9 +139,9 @@ static int fsl_mc_bus_uevent(const struct device *dev,
struct kobj_uevent_env *e
static int fsl_mc_dma_configure(struct device *dev)
{
+ const struct device_driver *drv = READ_ONCE(dev->driver);
struct device *dma_dev = dev;
struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
- struct fsl_mc_driver *mc_drv = to_fsl_mc_driver(dev->driver);
u32 input_id = mc_dev->icid;
int ret;
@@ -153,8 +153,8 @@ static int fsl_mc_dma_configure(struct device *dev)
else
ret = acpi_dma_configure_id(dev, DEV_DMA_COHERENT, &input_id);
- /* @mc_drv may not be valid when we're called from the IOMMU layer */
- if (!ret && dev->driver && !mc_drv->driver_managed_dma) {
+ /* @drv may not be valid when we're called from the IOMMU layer */
+ if (!ret && drv && !to_fsl_mc_driver(drv)->driver_managed_dma) {
ret = iommu_device_use_default_domain(dev);
if (ret)
arch_teardown_dma_ops(dev);
--
2.39.2.101.g768bb238c484.dirty
