netfilter: nft_payload: incorrect arithmetics when fetching VLAN header bits

stable inclusion
from stable-v5.10.164
commit 550efeff989b041f3746118c0ddd863c39ddc1aa
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6AOP8
CVE: CVE-2023-0179

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=550efeff989b041f3746118c0ddd863c39ddc1aa

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

commit 696e1a48 upstream.

If the offset + length goes over the ethernet + vlan header, then the
length is adjusted to copy the bytes that are within the boundaries of
the vlan_ethhdr scratchpad area. The remaining bytes beyond ethernet +
vlan header are copied directly from the skbuff data area.

Fix incorrect arithmetic operator: subtract, not add, the size of the
vlan header in case of double-tagged packets to adjust the length
accordingly to address CVE-2023-0179.
Reported-by: NDavide Ornaghi <d.ornaghi97@gmail.com>
Fixes: f6ae9f12 ("netfilter: nft_payload: add C-VLAN support")
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZiyang Xuan <william.xuanziyang@huawei.com>
Reviewed-by: NYue Haibing <yuehaibing@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

net/netfilter/nft_payload.c

@@ -62,7 +62,7 @@ nft_payload_copy_vlan(u32 *d, const struct sk_buff *skb, u8 offset, u8 len)
 			return false;
 
 		if (offset + len > VLAN_ETH_HLEN + vlan_hlen)
-			ethlen -= offset + len - VLAN_ETH_HLEN + vlan_hlen;
+			ethlen -= offset + len - VLAN_ETH_HLEN - vlan_hlen;
 
 		memcpy(dst_u8, vlanh + offset - vlan_hlen, ethlen);