[UBUNTU OEM-5.14, Jammy, HWE-5.17, Kinetic, OEM-6.0, Lunar, OEM-6.1, Unstable 1/1] netfilter: nft_payload: incorrect arithmetics when fetching VLAN header bits

[Thadeu Lima de Souza Cascardo]

From: Pablo Neira Ayuso <pablo at netfilter.org>

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: Davide Ornaghi <d.ornaghi97 at gmail.com>
Fixes: f6ae9f120dad ("netfilter: nft_payload: add C-VLAN support")
Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>
(cherry picked from commit 696e1a48b1a1b01edad542a1ef293665864a4dd0 net.git)
CVE-2023-0179
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 net/netfilter/nft_payload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index 4edd899aeb9b..d7de2ecb287e 100644
--- a/net/netfilter/nft_payload.c
+++ b/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);
 
-- 
2.34.1