[ 172/187] macvtap: zerocopy: validate vectors before building skb

[Greg Kroah-Hartman]

From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasowang@xxxxxxxxxx>

commit b92946e2919134ebe2a4083e4302236295ea2a73 upstream.

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@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Josh Boyer <jwboyer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/macvtap.c |   25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -528,9 +528,10 @@ static int zerocopy_sg_from_iovec(struct
 		}
 		base = (unsigned long)from->iov_base + offset1;
 		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)
 			/* put_page is in skb free */
 			return -EFAULT;
 		skb->data_len += len;
@@ -647,7 +648,7 @@ static ssize_t macvtap_get_user(struct 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) {
@@ -676,15 +677,31 @@ static ssize_t macvtap_get_user(struct 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


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