[PATCH v5 5/7] iommu/vt-d: Fix RB-tree corruption and Use-After-Free in probe

[Pranjal Shrivastava <praan@google.com>]

The intel_iommu_probe_device() function contains two pre-existing
memory safety issues on its error path:

1. The info->node RB-tree member is zero-initialized via kzalloc. If
   a device does not support ATS, the device_rbtree_insert() call is
   skipped. If a subsequent probe step fails, the error path jumps to
   device_rbtree_remove(), which misinterprets the zeroed node as
   a tree root and corrupts the device RB-tree.

2. The info structure is freed on failure, but the pointer remains
   linked to the device via dev_iommu_priv_set(). This leads to a
   Use-After-Free regression if the pointer is accessed later.

Fix these by explicitly initializing the RB-node as empty and guarding
its removal. Additionally, ensure dev_iommu_priv_set(dev, NULL) is
called before freeing the info structure in the error path.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/all/20260525205628.CD4431F000E9@smtp.kernel.org/
Suggested-by: Baolu Lu <baolu.lu@linux.intel.com>
Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/intel/iommu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 4d0e65bc131d..ed6d3a0203f5 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -157,7 +157,10 @@ static void device_rbtree_remove(struct device_domain_info *info)
 	unsigned long flags;
 
 	spin_lock_irqsave(&iommu->device_rbtree_lock, flags);
-	rb_erase(&info->node, &iommu->device_rbtree);
+	if (!RB_EMPTY_NODE(&info->node)) {
+		rb_erase(&info->node, &iommu->device_rbtree);
+		RB_CLEAR_NODE(&info->node);
+	}
 	spin_unlock_irqrestore(&iommu->device_rbtree_lock, flags);
 }
 
@@ -3254,6 +3257,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
 
 	info->dev = dev;
 	info->iommu = iommu;
+	RB_CLEAR_NODE(&info->node);
 	if (dev_is_pci(dev)) {
 		if (ecap_dev_iotlb_support(iommu->ecap) &&
 		    pci_ats_supported(pdev) &&
@@ -3316,6 +3320,7 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
 clear_rbtree:
 	device_rbtree_remove(info);
 free:
+	dev_iommu_priv_set(dev, NULL);
 	kfree(info);
 
 	return ERR_PTR(ret);
-- 
2.54.0.823.g6e5bcc1fc9-goog