[PATCH 9/9] virtio_ring: validate used buffer length

[Jason Wang]

This patch validate the used buffer length provided by the device
before trying to use it. This is done by record the in buffer length
in a new field in desc_state structure during virtqueue_add(), then we
can fail the virtqueue_get_buf() when we find the device is trying to
give us a used buffer length which is greater than the in buffer
length.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index d2ca0a7365f8..b8374a6144f3 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -69,6 +69,7 @@
 struct vring_desc_state_split {
 	void *data;			/* Data for callback. */
 	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
+	u64 buflen;			/* In buffer length */
 };
 
 struct vring_desc_state_packed {
@@ -76,6 +77,7 @@ struct vring_desc_state_packed {
 	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
 	u16 num;			/* Descriptor list length. */
 	u16 last;			/* The last desc state in a list. */
+	u64 buflen;			/* In buffer length */
 };
 
 struct vring_desc_extra {
@@ -490,6 +492,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	unsigned int i, n, avail, descs_used, prev, err_idx;
 	int head;
 	bool indirect;
+	u64 buflen = 0;
 
 	START_USE(vq);
 
@@ -571,6 +574,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 						     VRING_DESC_F_NEXT |
 						     VRING_DESC_F_WRITE,
 						     indirect);
+			buflen += sg->length;
 		}
 	}
 	/* Last one doesn't continue. */
@@ -605,6 +609,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 
 	/* Store token and indirect buffer state. */
 	vq->split.desc_state[head].data = data;
+	vq->split.desc_state[head].buflen = buflen;
 	if (indirect)
 		vq->split.desc_state[head].indir_desc = desc;
 	else
@@ -784,6 +789,11 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
 		BAD_RING(vq, "id %u is not a head!\n", i);
 		return NULL;
 	}
+	if (unlikely(*len > vq->split.desc_state[i].buflen)) {
+		BAD_RING(vq, "used len %d is larger than in buflen %lld\n",
+			*len, vq->split.desc_state[i].buflen);
+		return NULL;
+	}
 
 	/* detach_buf_split clears data, so grab it now. */
 	ret = vq->split.desc_state[i].data;
@@ -1062,6 +1072,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	unsigned int i, n, err_idx;
 	u16 head, id;
 	dma_addr_t addr;
+	u64 buflen = 0;
 
 	head = vq->packed.next_avail_idx;
 	desc = alloc_indirect_packed(total_sg, gfp);
@@ -1089,6 +1100,8 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 			desc[i].addr = cpu_to_le64(addr);
 			desc[i].len = cpu_to_le32(sg->length);
 			i++;
+			if (n >= out_sgs)
+				buflen += sg->length;
 		}
 	}
 
@@ -1141,6 +1154,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 	vq->packed.desc_state[id].data = data;
 	vq->packed.desc_state[id].indir_desc = desc;
 	vq->packed.desc_state[id].last = id;
+	vq->packed.desc_state[id].buflen = buflen;
 
 	vq->num_added += 1;
 
@@ -1176,6 +1190,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 	unsigned int i, n, c, descs_used, err_idx;
 	__le16 head_flags, flags;
 	u16 head, id, prev, curr, avail_used_flags;
+	u64 buflen = 0;
 
 	START_USE(vq);
 
@@ -1250,6 +1265,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 					1 << VRING_PACKED_DESC_F_AVAIL |
 					1 << VRING_PACKED_DESC_F_USED;
 			}
+			if (n >= out_sgs)
+				buflen += sg->length;
 		}
 	}
 
@@ -1268,6 +1285,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 	vq->packed.desc_state[id].data = data;
 	vq->packed.desc_state[id].indir_desc = ctx;
 	vq->packed.desc_state[id].last = prev;
+	vq->packed.desc_state[id].buflen = buflen;
 
 	/*
 	 * A driver MUST NOT make the first descriptor in the list
@@ -1455,6 +1473,11 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
 		BAD_RING(vq, "id %u is not a head!\n", id);
 		return NULL;
 	}
+	if (unlikely(*len > vq->packed.desc_state[id].buflen)) {
+		BAD_RING(vq, "used len %d is larger than in buflen %lld\n",
+			*len, vq->packed.desc_state[id].buflen);
+		return NULL;
+	}
 
 	/* detach_buf_packed clears data, so grab it now. */
 	ret = vq->packed.desc_state[id].data;
-- 
2.25.1