Commit 8e2ad411 authored by Willem de Bruijn's avatar Willem de Bruijn Committed by David S. Miller
Browse files

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: default avatarWillem de Bruijn <>
Signed-off-by: default avatarDavid S. Miller <>
parent 8208d21b
......@@ -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;
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,
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