Re: [PATCH net v3 3/5] ipv6: restrict mld_qrv to 255

[Kuniyuki Iwashima]

On Sun, 01 Nov 2026 14:12:01 +0800, Jiayuan Chen wrote:
> net.ipv6.mld_qrv only has a lower bound, but ipv6_mc_reset() stores it
> into the u8 inet6_dev::mc_qrv, so 256 wraps to 0 and the first MLDv2
> Query received on the interface trips the WARN_ON() in mld_update_qrv():
> 
> 	WARN_ON(idev->mc_qrv == 0);
> 
>   WARNING: net/ipv6/mcast.c:1327 at mld_query_work+0x1fd2/0x2cb0, CPU#3: kworker/3:1/2688
>   Workqueue: mld mld_query_work
>   RIP: 0010:mld_query_work+0x1fd2/0x2cb0
>   Call Trace:
>    <TASK>
>    process_one_work+0x93a/0x1b20
>    worker_thread+0x6d0/0x11d0
>    kthread+0x358/0x470
>    ret_from_fork+0x5b3/0x820
>    ret_from_fork_asm+0x1a/0x30
>    </TASK>
> 
> Make the sysctl a u8 like mc_qrv and switch to proc_dou8vec_minmax(),
> which rejects anything above 255, and document it.
> 
> Fixes: 2f711939d2ea ("ipv6: add sysctl_mld_qrv to configure query robustness variable")
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Fernando Fernandez Mancera <fmancera@xxxxxxx>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>

Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>