Commit 8e2ad411 authored Mar 08, 2016 by Willem de Bruijn Committed by David S. Miller Mar 11, 2016

macvtap: always pass ethernet header in linear



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 b9fb9ee0 ("macvtap: add GSO/csum offload support")
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 8208d21b

drivers/net/macvtap.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -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 = good_linear;
		else
		linear = macvtap16_to_cpu(q, vnet_hdr.hdr_len);
		if (linear > good_linear)
		linear = good_linear;
		else if (linear < ETH_HLEN)
		linear = ETH_HLEN;
		}

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

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