Re: [PATCH net v4] net/openvswitch: check Ethernet header length in key_extract()

On 25 Jul 2026, at 6:31, Cen Zhang (Microsoft) wrote:

When a packet arrives on an ARPHRD_NONE device (e.g. TUN),
ovs_flow_key_extract() trusts the user-provided skb->protocol field: if
it is ETH_P_TEB, the packet is classified as MAC_PROTO_ETHERNET and
key_extract() is called without ensuring the skb has ETH_HLEN (14) bytes
of linear data. key_extract() unconditionally pulls 2 * ETH_ALEN bytes
for MAC addresses and parse_ethertype() pulls 2 more, either of which
triggers a kernel BUG in __skb_pull() when the linear area is too small.

  kernel BUG at include/linux/skbuff.h:2848!
  RIP: 0010:key_extract+0xa7e/0xd90 net/openvswitch/flow.c:933
  ovs_flow_key_extract+0x419/0xa70
  ovs_vport_receive+0x222/0x390
  netdev_frame_hook+0x3e0/0x630
  tun_get_user+0x2d0c/0x38e0

Fixed by calling check_header() in key_extract() before accessing the
Ethernet header.

Fixes: 217ac77a3c25 ("openvswitch: allow L3 netdev ports")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Cen Zhang (Microsoft) <redacted>
---
v4: Update documentation and move variables into the Ethernet block.
v3: Use check_header() per review, fix format issue.
v2: Moved the check into key_extract() per Ilya Maximets.
Link: https://lore.kernel.org/all/20260721143602.64677-1-blbllhy@gmail.com (local)

Thanks for sending out a v4 with my comments fixed. The change looks good to me.

Reviewed-by:  Eelco Chaudron <echaudro@redhat.com>