Re: [PATCH net v5] net/openvswitch: check Ethernet header length in key_extract()

[Ilya Maximets]

On 7/31/26 12:20 AM, 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@xxxxxxxxxxxxx
> Reviewed-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
> Signed-off-by: Cen Zhang (Microsoft) <blbllhy@xxxxxxxxx>
> ---
> v5: Separate err declaration and initialization per review.
> 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/r/20260725043128.193164-1-blbllhy@xxxxxxxxx
Reviewed-by: Ilya Maximets <i.maximets@xxxxxxx>