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

From: Xie Yongji
Date: Mon May 17 2021 - 05:15:01 EST


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