Re: [PATCH net-next v5 1/2] net: hsr: require valid EOT supervision TLV

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

On 4/7/26 6:25 PM, 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, and properly linearizing the TLV header before
> access.
> 
> Assisted-by: Gemini:Gemini-3.1-flash
> Signed-off-by: Luka Gejak <luka.gejak@linux.dev>
> ---
>   net/hsr/hsr_forward.c | 20 +++++++++-----------
>   1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
> index 0aca859c88cb..eb89cc44eac0 100644
> --- a/net/hsr/hsr_forward.c
> +++ b/net/hsr/hsr_forward.c
> @@ -82,35 +82,33 @@ 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 */
> +	/* Get next TLV */
>   	total_length += hsr_sup_tag->tlv.HSR_TLV_length;
> -	if (!pskb_may_pull(skb, total_length))
> +	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
> -	 */
> +	/* If this is a RedBox supervision frame, verify additional data */
>   	if (hsr_sup_tlv->HSR_TLV_type == PRP_TLV_REDBOX_MAC) {
> -		/* tlv length must be a length of a mac address */
> +		/* TLV length must be the size of a MAC address */
>   		if (hsr_sup_tlv->HSR_TLV_length != sizeof(struct hsr_sup_payload))
>   			return false;
>   
> -		/* make sure another tlv follows */
> +		/* 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))
> +		if (!pskb_may_pull(skb, total_length + sizeof(struct hsr_sup_tlv)))

Hi Luka,

why is the length adjusted here? The current total length was adjusted 
correctly above see:

total_length += sizeof(struct hsr_sup_tlv) + hsr_sup_tlv->HSR_TLV_length;

Thanks,
Fernando.

>   			return false;
>   
> -		/* get next tlv */
> +		/* Get next TLV */
>   		skb_pull(skb, total_length);
>   		hsr_sup_tlv = (struct hsr_sup_tlv *)skb->data;
>   		skb_push(skb, total_length);
>   	}
>   
> -	/* end of tlvs must follow at the end */
> -	if (hsr_sup_tlv->HSR_TLV_type == HSR_TLV_EOT &&
> +	/* Supervision frame must end with EOT TLV */
> +	if (hsr_sup_tlv->HSR_TLV_type != HSR_TLV_EOT ||
>   	    hsr_sup_tlv->HSR_TLV_length != 0)
>   		return false;
>