[PATCH net 3/3] ibmveth: don't read an unset MAC header on transmit

[Doruk Tan Ozturk <doruk@0sec.ai>]

ibmveth_is_packet_unsupported(), called from ibmveth_start_xmit(), reads
the Ethernet header via eth_hdr(skb) to test the destination address.

On the AF_PACKET SOCK_RAW + PACKET_QDISC_BYPASS transmit path the skb
reaches ndo_start_xmit() with the MAC header unset, so eth_hdr(skb)
resolves to skb->head + (u16)~0 and the read is out of bounds.

On the TX path the L2 header is at skb->data, so use skb_eth_hdr(), as
done for the same class by
commit f5089008f90c ("macsec: don't read an unset MAC header in macsec_encrypt()")
and commit 96cc4b69581d ("macvlan: do not assume mac_header is set in macvlan_broadcast()").

Fixes: 6f2275433a2f ("ibmveth: Detect unsupported packets before sending to the hypervisor")
Cc: stable@vger.kernel.org
Found by 0sec automated security-research tooling (https://0sec.ai).
Assisted-by: 0sec:claude-opus-4-8
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
---
 drivers/net/ethernet/ibm/ibmveth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index 73e051d26b9d..88e8bdfbcd11 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c
@@ -1218,7 +1218,7 @@ static int ibmveth_is_packet_unsupported(struct sk_buff *skb,
 	struct ethhdr *ether_header;
 	int ret = 0;
 
-	ether_header = eth_hdr(skb);
+	ether_header = skb_eth_hdr(skb);
 
 	if (ether_addr_equal(ether_header->h_dest, netdev->dev_addr)) {
 		netdev_dbg(netdev, "veth doesn't support loopback packets, dropping packet.\n");
-- 
2.43.0