[PATCH v3 6/9] vsock/virtio: Move SKB allocation lower-bound check to callers

[Will Deacon <will@kernel.org>]

virtio_vsock_alloc_linear_skb() checks that the requested size is at
least big enough for the packet header (VIRTIO_VSOCK_SKB_HEADROOM).

Of the three callers of virtio_vsock_alloc_linear_skb(), only
vhost_vsock_alloc_skb() can potentially pass a packet smaller than the
header size and, as it already has a check against the maximum packet
size, extend its bounds checking to consider the minimum packet size
and remove the check from virtio_vsock_alloc_linear_skb().

Signed-off-by: Will Deacon <will@kernel.org>
---
 drivers/vhost/vsock.c        | 3 ++-
 include/linux/virtio_vsock.h | 3 ---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 1ad96613680e..24b7547b05a6 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -344,7 +344,8 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,
 
 	len = iov_length(vq->iov, out);
 
-	if (len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM)
+	if (len < VIRTIO_VSOCK_SKB_HEADROOM ||
+	    len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM)
 		return NULL;
 
 	/* len contains both payload and hdr */
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 4504ea29ff82..36dd0cd55368 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -57,9 +57,6 @@ virtio_vsock_alloc_linear_skb(unsigned int size, gfp_t mask)
 {
 	struct sk_buff *skb;
 
-	if (size < VIRTIO_VSOCK_SKB_HEADROOM)
-		return NULL;
-
 	skb = alloc_skb(size, mask);
 	if (!skb)
 		return NULL;
-- 
2.50.0.727.gbf7dc18ff4-goog