[PATCH v2 1/3] KVM: arm64: vgic-its: Handle errors from vgic_add_lpi

[Christoffer Dall <christoffer.dall@xxxxxxxxxx>]

During low memory conditions, we could be dereferencing a NULL pointer
when vgic_add_lpi fails to allocate memory.

Consider for example this call sequence:

  vgic_its_cmd_handle_mapi
      itte->irq = vgic_add_lpi(kvm, lpi_nr);
          update_lpi_config(kvm, itte->irq, NULL);
              ret = kvm_read_guest(kvm, propbase + irq->intid
	                                             ^^^^
						     kaboom?

Instead, return an error pointer from vgic_add_lpi and check the return
value from its single caller.

Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
---
Changes since v1:
 - Don't errornously get an extra kref refernce for the struct vgic_irq
 - Don't rework the entire error handling of the function, but follow
   what Marc suggested he prefers based on his fixup patch.
 virt/kvm/arm/vgic/vgic-its.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 07411cf..424f7a5 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -51,7 +51,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid)
 
 	irq = kzalloc(sizeof(struct vgic_irq), GFP_KERNEL);
 	if (!irq)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	INIT_LIST_HEAD(&irq->lpi_list);
 	INIT_LIST_HEAD(&irq->ap_list);
@@ -693,10 +693,11 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
 	u32 device_id = its_cmd_get_deviceid(its_cmd);
 	u32 event_id = its_cmd_get_id(its_cmd);
 	u32 coll_id = its_cmd_get_collection(its_cmd);
-	struct its_itte *itte;
+	struct its_itte *itte, *new_itte = NULL;
 	struct its_device *device;
 	struct its_collection *collection, *new_coll = NULL;
 	int lpi_nr;
+	struct vgic_irq *irq;
 
 	device = find_its_device(its, device_id);
 	if (!device)
@@ -720,7 +721,7 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
 
 	itte = find_itte(its, device_id, event_id);
 	if (!itte) {
-		itte = kzalloc(sizeof(struct its_itte), GFP_KERNEL);
+		new_itte = itte = kzalloc(sizeof(struct its_itte), GFP_KERNEL);
 		if (!itte) {
 			if (new_coll)
 				vgic_its_free_collection(its, coll_id);
@@ -733,7 +734,16 @@ static int vgic_its_cmd_handle_mapi(struct kvm *kvm, struct vgic_its *its,
 
 	itte->collection = collection;
 	itte->lpi = lpi_nr;
-	itte->irq = vgic_add_lpi(kvm, lpi_nr);
+
+	irq = vgic_add_lpi(kvm, lpi_nr);
+	if (IS_ERR(irq)) {
+		if (new_coll)
+			vgic_its_free_collection(its, coll_id);
+		kfree(new_itte);
+		return PTR_ERR(irq);
+	}
+	itte->irq = irq;
+
 	update_affinity_itte(kvm, itte);
 
 	/*
-- 
2.9.0

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