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Subject[ 172/187] macvtap: zerocopy: validate vectors before building skb
Date
From: Greg KH <gregkh@linuxfoundation.org>

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

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

From: Jason Wang <jasowang@redhat.com>

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@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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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