netdev - Re: [PATCH] net: mroute6.h: change type of mif6c_pifi to _

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Message-ID: <20230328191456.43d2222e@kernel.org>
Date:   Tue, 28 Mar 2023 19:14:56 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ganesh Babu <ganesh.babu@...nops.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: mroute6.h: change type of mif6c_pifi to __u32

On Tue, 28 Mar 2023 07:13:03 +0000 Ganesh Babu wrote:
> From a91f11fe060729d0009a3271e3a92cead88e2656 Mon Sep 17 00:00:00 2001
> From: "Ganesh Babu" <ganesh.babu@...nops.com>
> Date: Wed, 15 Mar 2023 15:01:39 +0530
> Subject: [PATCH] net: mroute6.h: change type of mif6c_pifi to __u32
> 
> Increase mif6c_pifi field in mif6ctl struct
> from 16 to 32 bits to support 32-bit ifindices.
> The field stores the physical interface (ifindex) for a multicast group.
> Passing a 32-bit ifindex via MRT6_ADD_MIF socket option
> from user space can cause unpredictable behavior in PIM6.
> Changing mif6c_pifi to __u32 allows kernel to handle
> 32-bit ifindex values without issues.

The patch is not formatted correctly.
Maybe try git send-email next time?

> diff --git a/include/uapi/linux/mroute6.h b/include/uapi/linux/mroute6.h
> index 1d90c21a6251..90e6e771beab 100644
> --- a/include/uapi/linux/mroute6.h
> +++ b/include/uapi/linux/mroute6.h
> @@ -75,7 +75,7 @@ struct mif6ctl {
>         mifi_t  mif6c_mifi;             /* Index of MIF */
>         unsigned char mif6c_flags;      /* MIFF_ flags */
>         unsigned char vifc_threshold;   /* ttl limit */
> -       __u16    mif6c_pifi;            /* the index of the physical IF */
> +       __u32    mif6c_pifi;            /* the index of the physical IF */

Unfortunately we can't do this. The structure is part of uAPI,
we can't change it's geometry. The kernel must maintain binary
backward compatibility. 

>         unsigned int vifc_rate_limit;   /* Rate limiter values (NI) */
>  };
> 
> --
> 2.11.0
> 
> Signed-off-by: Ganesh Babu <ganesh.babu@...nops.com>
> ---