Re: [syzbot] test uaf in iommufd_vfio_ioas

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Subject: test uaf in iommufd_vfio_ioas
Author: lizhi.xu@xxxxxxxxxxxxx

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 2af9b20dbb39

diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index e71523cbd0de..8d2dba522baf 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -137,6 +137,7 @@ static struct iommufd_object *iommufd_object_remove(struct iommufd_ctx *ictx,
 						    u32 id, bool extra_put)
 {
 	struct iommufd_object *obj;
+	struct iommufd_ioas *ioas;
 	XA_STATE(xas, &ictx->objects, id);
 
 	xa_lock(&ictx->objects);
@@ -159,7 +160,9 @@ static struct iommufd_object *iommufd_object_remove(struct iommufd_ctx *ictx,
 	}
 
 	xas_store(&xas, NULL);
-	if (ictx->vfio_ioas == container_of(obj, struct iommufd_ioas, obj))
+	ioas = container_of(obj, struct iommufd_ioas, obj);
+	ioas->obj = NULL;
+	if (ictx->vfio_ioas == ioas)
 		ictx->vfio_ioas = NULL;
 
 out_xa:
diff --git a/drivers/iommu/iommufd/vfio_compat.c b/drivers/iommu/iommufd/vfio_compat.c
index 6c810bf80f99..06317d0bd95e 100644
--- a/drivers/iommu/iommufd/vfio_compat.c
+++ b/drivers/iommu/iommufd/vfio_compat.c
@@ -140,6 +140,8 @@ int iommufd_vfio_ioas(struct iommufd_ucmd *ucmd)
 		ioas = iommufd_get_ioas(ucmd->ictx, cmd->ioas_id);
 		if (IS_ERR(ioas))
 			return PTR_ERR(ioas);
+		if (!ioas->obj)
+			return -EINVAL;
 		xa_lock(&ucmd->ictx->objects);
 		ucmd->ictx->vfio_ioas = ioas;
 		xa_unlock(&ucmd->ictx->objects);