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netfilter: nft_payload: simplify vlan header handling

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If the offset is within the ethernet + vlan header size boundary, then
rebuild the ethernet + vlan header and use it to copy the bytes to the
register. Otherwise, subtract the vlan header size from the offset and
fall back to use skb_copy_bits().

There is one corner case though: If the offset plus the length of the
payload instruction goes over the ethernet + vlan header boundary, then,
fetch as many bytes as possible from the rebuilt ethernet + vlan header
and fall back to copy the remaining bytes through skb_copy_bits().

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Florian Westphal <fw@strlen.de>
This commit is contained in:
Pablo Neira Ayuso 2019-10-31 15:51:21 +01:00
parent 25da5eb32c
commit f41f72d09e
1 changed files with 9 additions and 19 deletions
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28
net/netfilter/nft_payload.c
View file

@ -28,17 +28,22 @@ static bool
nft_payload_copy_vlan(u32 *d, const struct sk_buff *skb, u8 offset, u8 len)
{
int mac_off = skb_mac_header(skb) - skb->data;
u8 vlan_len, *vlanh, *dst_u8 = (u8 *) d;
u8 *vlanh, *dst_u8 = (u8 *) d;
struct vlan_ethhdr veth;
vlanh = (u8 *) &veth;
if (offset < ETH_HLEN) {
u8 ethlen = min_t(u8, len, ETH_HLEN - offset);
if (offset < VLAN_ETH_HLEN) {
u8 ethlen = len;
if (skb_copy_bits(skb, mac_off, &veth, ETH_HLEN))
return false;
veth.h_vlan_proto = skb->vlan_proto;
veth.h_vlan_TCI = htons(skb_vlan_tag_get(skb));
veth.h_vlan_encapsulated_proto = skb->protocol;
if (offset + len > VLAN_ETH_HLEN)
ethlen -= offset + len - VLAN_ETH_HLEN;
memcpy(dst_u8, vlanh + offset, ethlen);
@ -48,25 +53,10 @@ nft_payload_copy_vlan(u32 *d, const struct sk_buff *skb, u8 offset, u8 len)
dst_u8 += ethlen;
offset = ETH_HLEN;
} else if (offset >= VLAN_ETH_HLEN) {
} else {
offset -= VLAN_HLEN;
goto skip;
}
veth.h_vlan_TCI = htons(skb_vlan_tag_get(skb));
veth.h_vlan_encapsulated_proto = skb->protocol;
vlanh += offset;
vlan_len = min_t(u8, len, VLAN_ETH_HLEN - offset);
memcpy(dst_u8, vlanh, vlan_len);
len -= vlan_len;
if (!len)
return true;
dst_u8 += vlan_len;
skip:
return skb_copy_bits(skb, offset + mac_off, dst_u8, len) == 0;
}