From: Guillaume Nault <gnault@redhat.com>

Date: Wed, 6 Apr 2022 16:18:54 +0200

Subject: veth: Ensure eth header is in skb's linear part

Patch-mainline: v5.18-rc3

Git-commit: 726e2c5929de841fdcef4e2bf995680688ae1b87

References: git-fixes

After feeding a decapsulated packet to a veth device with act_mirred,

skb_headlen() may be 0. But veth_xmit() calls __dev_forward_skb(),

which expects at least ETH_HLEN byte of linear data (as

__dev_forward_skb2() calls eth_type_trans(), which pulls ETH_HLEN bytes

unconditionally).

Use pskb_may_pull() to ensure veth_xmit() respects this constraint.

kernel BUG at include/linux/skbuff.h:2328!

RIP: 0010:eth_type_trans+0xcf/0x140

Call Trace:

 <IRQ>

 __dev_forward_skb2+0xe3/0x160

 veth_xmit+0x6e/0x250 [veth]

 dev_hard_start_xmit+0xc7/0x200

 __dev_queue_xmit+0x47f/0x520

 ? skb_ensure_writable+0x85/0xa0

 ? skb_mpls_pop+0x98/0x1c0

 tcf_mirred_act+0x442/0x47e [act_mirred]

 tcf_action_exec+0x86/0x140

 fl_classify+0x1d8/0x1e0 [cls_flower]

 ? dma_pte_clear_level+0x129/0x1a0

 ? dma_pte_clear_level+0x129/0x1a0

 ? prb_fill_curr_block+0x2f/0xc0

 ? skb_copy_bits+0x11a/0x220

 __tcf_classify+0x58/0x110

 tcf_classify_ingress+0x6b/0x140

 __netif_receive_skb_core.constprop.0+0x47d/0xfd0

 ? __iommu_dma_unmap_swiotlb+0x44/0x90

 __netif_receive_skb_one_core+0x3d/0xa0

 netif_receive_skb+0x116/0x170

 be_process_rx+0x22f/0x330 [be2net]

 be_poll+0x13c/0x370 [be2net]

 __napi_poll+0x2a/0x170

 net_rx_action+0x22f/0x2f0

 __do_softirq+0xca/0x2a8

 __irq_exit_rcu+0xc1/0xe0

 common_interrupt+0x83/0xa0

Fixes: e314dbdc1c0d ("[NET]: Virtual ethernet device driver.")

Signed-off-by: Guillaume Nault <gnault@redhat.com>

Signed-off-by: David S. Miller <davem@davemloft.net>

Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>

---

 drivers/net/veth.c |    2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/veth.c

+++ b/drivers/net/veth.c

@@ -325,7 +325,7 @@ static netdev_tx_t veth_xmit(struct sk_b

 	rcu_read_lock();

 	rcv = rcu_dereference(priv->peer);

-	if (unlikely(!rcv)) {

+	if (unlikely(!rcv) || !pskb_may_pull(skb, ETH_HLEN)) {

 		kfree_skb(skb);

 		goto drop;

 	}