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Subject[PATCH 3.2 107/115] macvtap: always pass ethernet header in linear
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Willem de Bruijn <willemb@google.com>

[ 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>
---
drivers/net/macvtap.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -720,6 +720,8 @@ static ssize_t macvtap_get_user(struct m
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)
@@ -728,10 +730,11 @@ static ssize_t macvtap_get_user(struct m

if (!zerocopy) {
copylen = len;
- if (vnet_hdr.hdr_len > good_linear)
+ linear = vnet_hdr.hdr_len;
+ if (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,
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