macvtap: zerocopy: validate vectors before building skb

There're several reasons that the vectors need to be validated:

- Return error when caller provides vectors whose num is greater than UIO_MAXIOV.
- Linearize part of skb when userspace provides vectors grater than MAX_SKB_FRAGS.
- Return error when userspace provides vectors whose total length may exceed
- MAX_SKB_FRAGS * PAGE_SIZE.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index a4ff694cea228c4d98289c5ab3dde2f7d430005b..163559c16988329b57878b376d320a8ed8db5bfd 100644 (file)
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -529,9 +529,10 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                }
                base = (unsigned long)from->iov_base + offset;
                size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
+               if (i + size > MAX_SKB_FRAGS)
+                       return -EMSGSIZE;
                num_pages = get_user_pages_fast(base, size, 0, &page[i]);
-               if ((num_pages != size) ||
-                   (num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags)) {
+               if (num_pages != size) {
                        for (i = 0; i < num_pages; i++)
                                put_page(page[i]);
                        return -EFAULT;
@@ -651,7 +652,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
        int err;
        struct virtio_net_hdr vnet_hdr = { 0 };
        int vnet_hdr_len = 0;
-       int copylen;
+       int copylen = 0;
        bool zerocopy = false;
 
        if (q->flags & IFF_VNET_HDR) {
@@ -680,15 +681,31 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
        if (unlikely(len < ETH_HLEN))
                goto err;
 
+       err = -EMSGSIZE;
+       if (unlikely(count > UIO_MAXIOV))
+               goto err;
+
        if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY))
                zerocopy = true;
 
        if (zerocopy) {
+               /* Userspace may produce vectors with count greater than
+                * MAX_SKB_FRAGS, so we need to linearize parts of the skb
+                * to let the rest of data to be fit in the frags.
+                */
+               if (count > MAX_SKB_FRAGS) {
+                       copylen = iov_length(iv, count - MAX_SKB_FRAGS);
+                       if (copylen < vnet_hdr_len)
+                               copylen = 0;
+                       else
+                               copylen -= vnet_hdr_len;
+               }
                /* There are 256 bytes to be copied in skb, so there is enough
                 * room for skb expand head in case it is used.
                 * The rest buffer is mapped from userspace.
                 */
-               copylen = vnet_hdr.hdr_len;
+               if (copylen < vnet_hdr.hdr_len)
+                       copylen = vnet_hdr.hdr_len;
                if (!copylen)
                        copylen = GOODCOPY_LEN;
        } else