Re: [PATCH net-next v4 1/2] net: hsr: require valid EOT supervision TLV

[Fernando Fernandez Mancera <fmancera@suse.de>]

On 4/1/26 11:23 AM, luka.gejak@linux.dev wrote:
> From: Luka Gejak <luka.gejak@linux.dev>
> 
> Supervision frames are only valid if terminated with a zero-length EOT
> TLV. The current check fails to reject non-EOT entries as the terminal
> TLV, potentially allowing malformed supervision traffic.
> 
> Fix this by strictly requiring the terminal TLV to be HSR_TLV_EOT
> with a length of zero.
> 
> Reviewed-by: Felix Maurer <fmaurer@redhat.com>
> Signed-off-by: Luka Gejak <luka.gejak@linux.dev>
> ---
>   net/hsr/hsr_forward.c | 41 ++++++++++++++++++++++-------------------
>   1 file changed, 22 insertions(+), 19 deletions(-)
> 
> diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
> index 0aca859c88cb..17b705235c4a 100644
> --- a/net/hsr/hsr_forward.c
> +++ b/net/hsr/hsr_forward.c
> @@ -82,39 +82,42 @@ static bool is_supervision_frame(struct hsr_priv *hsr, struct sk_buff *skb)
>   	    hsr_sup_tag->tlv.HSR_TLV_length != sizeof(struct hsr_sup_payload))
>   		return false;
>   
> -	/* Get next tlv */
> +	/* Advance past the first TLV payload to reach next TLV header */
>   	total_length += hsr_sup_tag->tlv.HSR_TLV_length;
> -	if (!pskb_may_pull(skb, total_length))
> +	/* Linearize next TLV header before access */
> +	if (!pskb_may_pull(skb, total_length + sizeof(struct hsr_sup_tlv)))
>   		return false;
>   	skb_pull(skb, total_length);
>   	hsr_sup_tlv = (struct hsr_sup_tlv *)skb->data;
>   	skb_push(skb, total_length);
>   
> -	/* if this is a redbox supervision frame we need to verify
> -	 * that more data is available
> +	/* Walk through TLVs to find end-of-TLV marker, skipping any unknown
> +	 * extension TLVs to maintain forward compatibility.
>   	 */
> -	if (hsr_sup_tlv->HSR_TLV_type == PRP_TLV_REDBOX_MAC) {
> -		/* tlv length must be a length of a mac address */
> -		if (hsr_sup_tlv->HSR_TLV_length != sizeof(struct hsr_sup_payload))
> -			return false;
> +	for (;;) {
> +		if (hsr_sup_tlv->HSR_TLV_type == HSR_TLV_EOT &&
> +		    hsr_sup_tlv->HSR_TLV_length == 0)
> +			return true;
>   

I do not follow this approach, why a loop? From IEC 62439-3, I do not 
understand that supervision frames could have multiple 
PRP_TLV_REDBOX_MAC TLVs. The current code handles the TLVs correctly.

Which makes me wonder, how are you testing this? Do you have some 
hardware with HSR/PRP support that is sending these frames? If so, which 
one? Are you testing this using a HSR/PRP environment with purely Linux 
devices?

Thanks,
Fernando.

> -		/* make sure another tlv follows */
> -		total_length += sizeof(struct hsr_sup_tlv) + hsr_sup_tlv->HSR_TLV_length;
> -		if (!pskb_may_pull(skb, total_length))
> +		/* Validate known TLV types */
> +		if (hsr_sup_tlv->HSR_TLV_type == PRP_TLV_REDBOX_MAC) {
> +			if (hsr_sup_tlv->HSR_TLV_length !=
> +			    sizeof(struct hsr_sup_payload))
> +				return false;
> +		}
> +
> +		/* Advance past current TLV: header + payload */
> +		total_length += sizeof(struct hsr_sup_tlv) +
> +				hsr_sup_tlv->HSR_TLV_length;
> +		/* Linearize next TLV header before access */
> +		if (!pskb_may_pull(skb,
> +				   total_length + sizeof(struct hsr_sup_tlv)))
>   			return false;
>   
> -		/* get next tlv */
>   		skb_pull(skb, total_length);
>   		hsr_sup_tlv = (struct hsr_sup_tlv *)skb->data;
>   		skb_push(skb, total_length);
>   	}