Re: [PATCH dpdk v5 4/5] net: parse L3 protocol after MPLS labels

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 18 May 2026 15:27:18 +0200
Robin Jarry <rjarry@redhat.com> wrote:

> rte_net_get_ptype stops at the MPLS layer and never identifies the L3
> protocol of the payload. Also, the label parsing uses a fixed maximum of
> 5 headers instead of checking the bottom of stack bit.
> 
> Use the bottom of stack bit to consume all labels and inspect the first
> nibble of the payload to determine if it is IPv4 or IPv6.
> 
> Add test cases to verify this works. Ensure that an unknown protocol
> after MPLS (e.g. ARP) does not produce a bogus L3 type.
> 
> Signed-off-by: Robin Jarry <rjarry@redhat.com>
> ---

AI spotted similar potential uint8_t overflow here.

Patch 4/5: net: parse L3 protocol after MPLS labels

Warning: same uint8_t l2_len concern as patch 2. The old loop was capped
at MAX_MPLS_HDR (5); the new "do { } while (!mh->bs)" is bounded only by
packet length, so a deep label stack wraps l2_len.

Info: the local is named "nimble" (and the read into nimble_copy);
the comment says "first 4 bits", i.e. the nibble. Likely meant "nibble".