Commit c9897252a66b for kernel

commit c9897252a66b43a17d04c19bc7303fd6539a56ba
Merge: b7ff0e7a9ae3 498c631f9c6d
Author: Jakub Kicinski <kuba@kernel.org>
Date:   Thu Oct 29 09:11:22 2026 -0700

    Merge branch 'net-fix-eth_type_trans-crashes-on-skbs-coming-from-the-stack'

    Eric Dumazet says:

    ====================
    net: fix eth_type_trans() crashes on skbs coming from the stack

    eth_type_trans() assumes ETH_HLEN bytes are present in skb->head.
    NIC drivers always provide this, and they should keep using the fast
    version, without an extra pskb_may_pull().

    Devices looping skbs from their transmit path back to their receive
    path get skbs built by the stack instead. tc actions (act_vlan pop_eth,
    act_ife decode), BPF helpers (bpf_skb_change_head() before a redirect)
    or OVS actions (pop_eth followed by pop_mpls/pop_nsh) can leave fewer
    than ETH_HLEN bytes in the linear part, and eth_type_trans() then hits
    the BUG() in __skb_pull().

    Instead of fixing every producer, or adding a check to all
    eth_type_trans() users, fix the few consumers exposed to this:

    - Patch 1 adds eth_type_trans_careful(), which pulls the Ethernet
      header first and returns a drop reason on failure.
    - Patch 2 uses it in loopback_xmit().
    - Patch 3 uses it in __dev_forward_skb2(), used by BPF redirects to
      ingress and by veth, macvlan, ipvlan, netdevsim and l2tp_eth.
    - Patch 4 uses it in OVS internal_dev_recv(), covering both the MPLS
      (TEB) and NSH pop cases at once (only the MPLS case was tested).
    - Patch 5 (from Jamal) fixes act_ife decode on egress, which was
      consuming the inner Ethernet header. This is no longer a crash after
      patch 2, but egress decode never delivered a correct frame.

    Other eth_type_trans() users already pull the header or never see
    such skbs:
    - vrf_process_v{4,6}_outbound() already pull ETH_HLEN + IP header
      before vrf_local_xmit().
    - tun already uses pskb_may_pull_reason(skb, ETH_HLEN).
    - XDP: bpf_xdp_adjust_head() and bpf_xdp_adjust_tail() keep at least
      ETH_HLEN bytes in the linear part, and multi-buffer tail shrinking
      only trims frags.

    Tested under virtme-ng with AF_PACKET reproducers. Without the series,
    all four cases crash in eth_type_trans():
    - lo egress "action vlan pop_eth", eth/eth/8192 bytes frame
    - lo egress "action ife decode pipe", IFE frame with 8192 bytes payload
    - lo egress "action vlan pop_eth continue", then a BPF program doing
      bpf_skb_change_head(skb, 1, 0) + bpf_redirect(veth1, BPF_F_INGRESS)
    - OVS flow "pop_eth,pop_mpls(0x6558),0" to the internal port,
      eth/mpls/eth/4096 bytes frame
    With the series, no crash. An ICMP echo inside an IFE frame decoded
    on lo egress is now received and answered. Normal traffic on lo,
    veth (including 8000 byte pings) and vrf is unchanged.

    Link: https://lore.kernel.org/netdev/20261005052249.1914367-2-weir@nebusec.ai/
    Link: https://lore.kernel.org/netdev/ACT-N6N4.v3.r0.20261023200137-4@mojatatu.com/
    v1: https://lore.kernel.org/netdev/20261027082604.1485903-1-edumazet@kernel.org/
    ====================

    Link: https://patch.msgid.link/20261028122703.2093730-1-edumazet@kernel.org
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>