[PATCH] iommufd: Fix UAF in selftest IOPF reporting

IOMMUFD selftest TRIGGER_IOPF borrows an attach handle from
group->pasid_array without synchronizing against PASID detach,
then a concurrent iommu_report_device_fault() can dereference
that borrowed handle's domain pointer after the detach erases
the handle and frees the backing struct iommufd_attach_handle.
TRIGGER_IOPF then dereferences the freed handle, causing a UAF.

Fix by adding a iopf_rwsem in mock_dev to follow the expected design
of a real driver. Hold its read side across the whole
iommu_report_device_fault() call, and its write side around every
path that attaches, detaches, or replaces a device domain.
This can block new reports and drains in-flight reports before an old
attach handle or the IOPF fault parameter can be removed.
Also take the write side while registering a mock device, since
it can invoke the mock driver's default-domain attach callback.

Closes: https://lore.kernel.org/all/D5E3AA41600B2056+f4e15662-bd2b-43ea-91cb-518de429e72c@smail.nju.edu.cn/
Fixes: ddee19971081 ("iommufd/selftest: Add IOPF support for mock device")
Cc: [email protected]
Suggested-by: Jason Gunthorpe <[email protected]>
Assisted-by: Codex:gpt-5.6-terra
Signed-off-by: Peiyang He <[email protected]>
---
 drivers/iommu/iommufd/selftest.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
index af07c642a526..727b59799d5f 100644
--- a/drivers/iommu/iommufd/selftest.c
+++ b/drivers/iommu/iommufd/selftest.c
@@ -177,6 +177,7 @@ struct mock_dev {
 	struct device dev;
 	struct mock_viommu *viommu;
 	struct rw_semaphore viommu_rwsem;
+	struct rw_semaphore iopf_rwsem;
 	unsigned long flags;
 	unsigned long vdev_id;
 	int id;
@@ -997,6 +998,7 @@ static struct mock_dev *mock_dev_create(unsigned long dev_flags)
 		return ERR_PTR(-ENOMEM);
 
 	init_rwsem(&mdev->viommu_rwsem);
+	init_rwsem(&mdev->iopf_rwsem);
 	device_initialize(&mdev->dev);
 	mdev->flags = dev_flags;
 	mdev->dev.release = mock_dev_release;
@@ -1022,7 +1024,9 @@ static struct mock_dev *mock_dev_create(unsigned long dev_flags)
 		goto err_put;
 	}
 
+	down_write(&mdev->iopf_rwsem);
 	rc = iommu_mock_device_add(&mdev->dev, &mock_iommu.iommu_dev);
+	up_write(&mdev->iopf_rwsem);
 	if (rc)
 		goto err_put;
 	return mdev;
@@ -1077,7 +1081,9 @@ static int iommufd_test_mock_domain(struct iommufd_ucmd *ucmd,
 	}
 	sobj->idev.idev = idev;
 
+	down_write(&sobj->idev.mock_dev->iopf_rwsem);
 	rc = iommufd_device_attach(idev, IOMMU_NO_PASID, &pt_id);
+	up_write(&sobj->idev.mock_dev->iopf_rwsem);
 	if (rc)
 		goto out_unbind;
 
@@ -1092,7 +1098,9 @@ static int iommufd_test_mock_domain(struct iommufd_ucmd *ucmd,
 	return 0;
 
 out_detach:
+	down_write(&sobj->idev.mock_dev->iopf_rwsem);
 	iommufd_device_detach(idev, IOMMU_NO_PASID);
+	up_write(&sobj->idev.mock_dev->iopf_rwsem);
 out_unbind:
 	iommufd_device_unbind(idev);
 out_mdev:
@@ -1136,7 +1144,9 @@ static int iommufd_test_mock_domain_replace(struct iommufd_ucmd *ucmd,
 	if (IS_ERR(sobj))
 		return PTR_ERR(sobj);
 
+	down_write(&sobj->idev.mock_dev->iopf_rwsem);
 	rc = iommufd_device_replace(sobj->idev.idev, IOMMU_NO_PASID, &pt_id);
+	up_write(&sobj->idev.mock_dev->iopf_rwsem);
 	if (rc)
 		goto out_sobj;
 
@@ -1739,10 +1749,16 @@ static int iommufd_test_trigger_iopf(struct iommufd_ucmd *ucmd,
 {
 	struct iopf_fault event = {};
 	struct iommufd_device *idev;
+	struct mock_dev *mdev;
 
 	idev = iommufd_get_device(ucmd, cmd->trigger_iopf.dev_id);
 	if (IS_ERR(idev))
 		return PTR_ERR(idev);
+	if (!iommufd_selftest_is_mock_dev(idev->dev)) {
+		iommufd_put_object(ucmd->ictx, &idev->obj);
+		return -EINVAL;
+	}
+	mdev = to_mock_dev(idev->dev);
 
 	event.fault.prm.flags = IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE;
 	if (cmd->trigger_iopf.pasid != IOMMU_NO_PASID)
@@ -1753,7 +1769,9 @@ static int iommufd_test_trigger_iopf(struct iommufd_ucmd *ucmd,
 	event.fault.prm.grpid = cmd->trigger_iopf.grpid;
 	event.fault.prm.perm = cmd->trigger_iopf.perm;
 
+	down_read(&mdev->iopf_rwsem);
 	iommu_report_device_fault(idev->dev, &event);
+	up_read(&mdev->iopf_rwsem);
 	iommufd_put_object(ucmd->ictx, &idev->obj);
 
 	return 0;
@@ -1861,14 +1879,19 @@ static int iommufd_test_pasid_attach(struct iommufd_ucmd *ucmd,
 	if (IS_ERR(sobj))
 		return PTR_ERR(sobj);
 
+	down_write(&sobj->idev.mock_dev->iopf_rwsem);
 	rc = iommufd_device_attach(sobj->idev.idev, cmd->pasid_attach.pasid,
 				   &cmd->pasid_attach.pt_id);
+	up_write(&sobj->idev.mock_dev->iopf_rwsem);
 	if (rc)
 		goto out_sobj;
 
 	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
-	if (rc)
+	if (rc) {
+		down_write(&sobj->idev.mock_dev->iopf_rwsem);
 		iommufd_device_detach(sobj->idev.idev, cmd->pasid_attach.pasid);
+		up_write(&sobj->idev.mock_dev->iopf_rwsem);
+	}
 
 out_sobj:
 	iommufd_put_object(ucmd->ictx, &sobj->obj);
@@ -1885,8 +1908,10 @@ static int iommufd_test_pasid_replace(struct iommufd_ucmd *ucmd,
 	if (IS_ERR(sobj))
 		return PTR_ERR(sobj);
 
+	down_write(&sobj->idev.mock_dev->iopf_rwsem);
 	rc = iommufd_device_replace(sobj->idev.idev, cmd->pasid_attach.pasid,
 				    &cmd->pasid_attach.pt_id);
+	up_write(&sobj->idev.mock_dev->iopf_rwsem);
 	if (rc)
 		goto out_sobj;
 
@@ -1906,7 +1931,9 @@ static int iommufd_test_pasid_detach(struct iommufd_ucmd *ucmd,
 	if (IS_ERR(sobj))
 		return PTR_ERR(sobj);
 
+	down_write(&sobj->idev.mock_dev->iopf_rwsem);
 	iommufd_device_detach(sobj->idev.idev, cmd->pasid_detach.pasid);
+	up_write(&sobj->idev.mock_dev->iopf_rwsem);
 	iommufd_put_object(ucmd->ictx, &sobj->obj);
 	return 0;
 }
@@ -1917,7 +1944,9 @@ void iommufd_selftest_destroy(struct iommufd_object *obj)
 
 	switch (sobj->type) {
 	case TYPE_IDEV:
+		down_write(&sobj->idev.mock_dev->iopf_rwsem);
 		iommufd_device_detach(sobj->idev.idev, IOMMU_NO_PASID);
+		up_write(&sobj->idev.mock_dev->iopf_rwsem);
 		iommufd_device_unbind(sobj->idev.idev);
 		mock_dev_destroy(sobj->idev.mock_dev);
 		break;

base-commit: 075b74841bd0065a3bda3440873c747938e69b68
-- 
2.43.0