On 20 May 2025, at 6:13, Faicker Mo wrote:
> The unexpected MPLS packet may not end with the bottom label stack.
> When there are many stacks, The label count value has wrapped around.
> A dead loop occurs, soft lockup/CPU stuck finally.
>
> stack backtrace:
> UBSAN: array-index-out-of-bounds in
> /build/linux-0Pa0xK/linux-5.15.0/net/openvswitch/flow.c:662:26
> index -1 is out of range for type '__be32 [3]'
> CPU: 34 PID: 0 Comm: swapper/34 Kdump: loaded Tainted: G OE
> 5.15.0-121-generic #131-Ubuntu
> Hardware name: Dell Inc. PowerEdge C6420/0JP9TF, BIOS 2.12.2 07/14/2021
> Call Trace:
> <IRQ>
> show_stack+0x52/0x5c
> dump_stack_lvl+0x4a/0x63
> dump_stack+0x10/0x16
> ubsan_epilogue+0x9/0x36
> __ubsan_handle_out_of_bounds.cold+0x44/0x49
> key_extract_l3l4+0x82a/0x840 [openvswitch]
> ? kfree_skbmem+0x52/0xa0
> key_extract+0x9c/0x2b0 [openvswitch]
> ovs_flow_key_extract+0x124/0x350 [openvswitch]
> ovs_vport_receive+0x61/0xd0 [openvswitch]
> ? kernel_init_free_pages.part.0+0x4a/0x70
> ? get_page_from_freelist+0x353/0x540
> netdev_port_receive+0xc4/0x180 [openvswitch]
> ? netdev_port_receive+0x180/0x180 [openvswitch]
> netdev_frame_hook+0x1f/0x40 [openvswitch]
> __netif_receive_skb_core.constprop.0+0x23a/0xf00
> __netif_receive_skb_list_core+0xfa/0x240
> netif_receive_skb_list_internal+0x18e/0x2a0
> napi_complete_done+0x7a/0x1c0
> bnxt_poll+0x155/0x1c0 [bnxt_en]
> __napi_poll+0x30/0x180
> net_rx_action+0x126/0x280
> ? bnxt_msix+0x67/0x80 [bnxt_en]
> handle_softirqs+0xda/0x2d0
> irq_exit_rcu+0x96/0xc0
> common_interrupt+0x8e/0xa0
> </IRQ>
>
> Signed-off-by: Faicker Mo <faicker...@zenlayer.com>
> ---
> net/openvswitch/flow.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> index 8a848ce72e29..834b1b9110ac 100644
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -805,6 +805,8 @@ static int key_extract_l3l4(struct sk_buff *skb, struct
> sw_flow_key *key)
> if (label_count <= MPLS_LABEL_DEPTH)
> memcpy(&key->mpls.lse[label_count - 1], &lse,
> MPLS_HLEN);
> + else if (unlikely(label_count == 255))
> + return 0;
Thanks for finding and solving this issue, Faicker. I think that if we hit 255
stack labels, it's safe to say the packet is invalid, and we should probably
return -EINVAL. This also makes sense because the inner_network_header is not
correct based on the terminated decode.
>
> skb_set_inner_network_header(skb, skb->mac_len +
> label_count * MPLS_HLEN);
> --
> 2.34.1
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