Re: [PATCH net-next v3] net: mctp: don't require received header reserved bits to be zero

[Paolo Abeni]

On 4/13/26 10:03 AM, wit_yuan wrote:
> From: Yuan Zhaoming <yuanzm2@xxxxxxxxxx>
> 
> From the MCTP Base specification (DSP0236 v1.2.1), the first byte of
> the MCTP header contains a 4 bit reserved field, and 4 bit version.
> 
> On our current receive path, we require those 4 reserved bits to be
> zero, but the 9500-8i card is non-conformant, and may set these
> reserved bits.
> 
> DSP0236 states that the reserved bits must be written as zero, and
> ignored when read. While the device might not conform to the former,
> we should accept these message to conform to the latter.
> 
> Relax our check on the MCTP version byte to allow non-zero bits in the
> reserved field.
> 
> Signed-off-by: Yuan Zhaoming <yuanzm2@xxxxxxxxxx>

The net-next tree is currently closed for the merge window, but IMHO
this change could be considered a fix. Please repost for 'net' and add a
suitable fixes tag.

> ---
> v2: https://lore.kernel.org/netdev/20260410144339.0d1b289a@xxxxxxxxxx/T/#t
> v1: https://lore.kernel.org/netdev/ff147a3f0d27ef2aa6026cc86f9113d56a8c61ac.camel@xxxxxxxxxxxxxxxxxxxx/T/#t
> ---
>  include/net/mctp.h | 3 +++
>  net/mctp/route.c   | 8 ++++++--
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/mctp.h b/include/net/mctp.h
> index e1e0a69..d8bf907 100644
> --- a/include/net/mctp.h
> +++ b/include/net/mctp.h
> @@ -26,6 +26,9 @@ struct mctp_hdr {
>  #define MCTP_VER_MIN	1
>  #define MCTP_VER_MAX	1
>  
> +/* Definitions for ver field */
> +#define MCTP_HDR_VER_MASK	GENMASK(3, 0)
> +
>  /* Definitions for flags_seq_tag field */
>  #define MCTP_HDR_FLAG_SOM	BIT(7)
>  #define MCTP_HDR_FLAG_EOM	BIT(6)
> diff --git a/net/mctp/route.c b/net/mctp/route.c
> index e69c6f7..62517c9 100644
> --- a/net/mctp/route.c
> +++ b/net/mctp/route.c
> @@ -439,6 +439,7 @@ static int mctp_dst_input(struct mctp_dst *dst, struct sk_buff *skb)
>  	struct mctp_hdr *mh;
>  	unsigned int netid;
>  	unsigned long f;
> +	u8 ver;
>  	u8 tag, flags;
>  	int rc;

Please respect the reverse christmas tree order above.

/P