[RFC PATCH 17/17] virtio_ring: Add validation for used length

[Xie Yongji]

This adds validation for used length (might come
from an untrusted device) when it will be used by
virtio device driver.

Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index d999a1d6d271..7d4845d06f21 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -68,11 +68,13 @@
 struct vring_desc_state_split {
 	void *data;			/* Data for callback. */
 	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
+	u32 in_len;			/* Total length of writable buffer */
 };
 
 struct vring_desc_state_packed {
 	void *data;			/* Data for callback. */
 	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
+	u32 in_len;			/* Total length of writable buffer */
 	u16 num;			/* Descriptor list length. */
 	u16 last;			/* The last desc state in a list. */
 };
@@ -486,7 +488,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	struct scatterlist *sg;
 	struct vring_desc *desc;
-	unsigned int i, n, avail, descs_used, prev, err_idx;
+	unsigned int i, n, avail, descs_used, prev, err_idx, in_len = 0;
 	int head;
 	bool indirect;
 
@@ -570,6 +572,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 						     VRING_DESC_F_NEXT |
 						     VRING_DESC_F_WRITE,
 						     indirect);
+			in_len += sg->length;
 		}
 	}
 	/* Last one doesn't continue. */
@@ -604,6 +607,7 @@ 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].in_len = in_len;
 	if (indirect)
 		vq->split.desc_state[head].indir_desc = desc;
 	else
@@ -784,6 +788,10 @@ 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].in_len < *len)) {
+		BAD_RING(vq, "id %u has invalid length: %u!\n", i, *len);
+		return NULL;
+	}
 
 	/* detach_buf_split clears data, so grab it now. */
 	ret = vq->split.desc_state[i].data;
@@ -1059,7 +1067,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 {
 	struct vring_packed_desc *desc;
 	struct scatterlist *sg;
-	unsigned int i, n, err_idx;
+	unsigned int i, n, err_idx, in_len = 0;
 	u16 head, id;
 	dma_addr_t addr;
 
@@ -1084,6 +1092,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 			if (vring_mapping_error(vq, addr))
 				goto unmap_release;
 
+			in_len += (n < out_sgs) ? 0 : sg->length;
 			desc[i].flags = cpu_to_le16(n < out_sgs ?
 						0 : VRING_DESC_F_WRITE);
 			desc[i].addr = cpu_to_le64(addr);
@@ -1141,6 +1150,7 @@ 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].in_len = in_len;
 
 	vq->num_added += 1;
 
@@ -1173,7 +1183,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	struct vring_packed_desc *desc;
 	struct scatterlist *sg;
-	unsigned int i, n, c, descs_used, err_idx;
+	unsigned int i, n, c, descs_used, err_idx, in_len = 0;
 	__le16 head_flags, flags;
 	u16 head, id, prev, curr, avail_used_flags;
 
@@ -1223,6 +1233,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 			if (vring_mapping_error(vq, addr))
 				goto unmap_release;
 
+			in_len += (n < out_sgs) ? 0 : sg->length;
 			flags = cpu_to_le16(vq->packed.avail_used_flags |
 				    (++c == total_sg ? 0 : VRING_DESC_F_NEXT) |
 				    (n < out_sgs ? 0 : VRING_DESC_F_WRITE));
@@ -1268,6 +1279,7 @@ 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].in_len = in_len;
 
 	/*
 	 * A driver MUST NOT make the first descriptor in the list
@@ -1456,6 +1468,10 @@ 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].in_len < *len)) {
+		BAD_RING(vq, "id %u has invalid length: %u!\n", id, *len);
+		return NULL;
+	}
 
 	/* detach_buf_packed clears data, so grab it now. */
 	ret = vq->packed.desc_state[id].data;
-- 
2.11.0