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macvtap: always pass ethernet header in linear

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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>
This commit is contained in:
Willem de Bruijn 2016-03-08 15:18:54 -05:00 committed by David S. Miller
parent 8208d21bf3
commit 8e2ad4113c
1 changed files with 6 additions and 3 deletions
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9
drivers/net/macvtap.c
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@ -760,6 +760,8 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
macvtap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
if (copylen > good_linear)
copylen = good_linear;
else if (copylen < ETH_HLEN)
copylen = ETH_HLEN;
linear = copylen;
i = *from;
iov_iter_advance(&i, copylen);
@ -769,10 +771,11 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
if (!zerocopy) {
copylen = len;
if (macvtap16_to_cpu(q, vnet_hdr.hdr_len) > good_linear)
linear = macvtap16_to_cpu(q, vnet_hdr.hdr_len);
if (linear > good_linear)
linear = good_linear;
else
linear = macvtap16_to_cpu(q, vnet_hdr.hdr_len);
else if (linear < ETH_HLEN)
linear = ETH_HLEN;
}
skb = macvtap_alloc_skb(&q->sk, MACVTAP_RESERVE, copylen,