macvtap: always pass ethernet header in linear

[ Upstream commit 8e2ad4113ce4671686740f808ff2795395c39eef ]

The stack expects link layer headers in the skb linear section.
Macvtap can create skbs with llheader in frags in edge cases:
when (IFF_VNET_HDR is off or vnet_hdr.hdr_len < ETH_HLEN) and
prepad + len > PAGE_SIZE and vnet_hdr.flags has no or bad csum.

Add checks to ensure linear is always at least ETH_HLEN.
At this point, len is already ensured to be >= ETH_HLEN.

For backwards compatiblity, rounds up short vnet_hdr.hdr_len.
This differs from tap and packet, which return an error.

Fixes b9fb9ee07e67 ("macvtap: add GSO/csum offload support")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: don't use macvtap16_to_cpu()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 7300447..2fcdede 100644 (file)
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -720,6 +720,8 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
                copylen = vnet_hdr.hdr_len ? vnet_hdr.hdr_len : GOODCOPY_LEN;
                if (copylen > good_linear)
                        copylen = good_linear;
                copylen = vnet_hdr.hdr_len ? vnet_hdr.hdr_len : GOODCOPY_LEN;
                if (copylen > good_linear)
                        copylen = good_linear;

+               else if (copylen < ETH_HLEN)
+                       copylen = ETH_HLEN;

                linear = copylen;
                if (iov_pages(iv, vnet_hdr_len + copylen, count)
                    <= MAX_SKB_FRAGS)
                linear = copylen;
                if (iov_pages(iv, vnet_hdr_len + copylen, count)
                    <= MAX_SKB_FRAGS)


@@ -728,10 +730,11 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 
        if (!zerocopy) {
                copylen = len;
 
        if (!zerocopy) {
                copylen = len;

-               if (vnet_hdr.hdr_len > good_linear)
+               linear = vnet_hdr.hdr_len;
+               if (linear > good_linear)

                        linear = good_linear;
                        linear = good_linear;

-               else
-                       linear = vnet_hdr.hdr_len;
+               else if (linear < ETH_HLEN)
+                       linear = ETH_HLEN;

        }
 
        skb = macvtap_alloc_skb(&q->sk, MACVTAP_RESERVE, copylen,
        }
 
        skb = macvtap_alloc_skb(&q->sk, MACVTAP_RESERVE, copylen,