Re: [PATCH net v3 4/5] ipv4: restrict igmp_qrv to 255

[Kuniyuki Iwashima]

On Sun, 01 Nov 2026 14:12:02 +0800, Jiayuan Chen wrote:
> net.ipv4.igmp_qrv only has a lower bound, but ip_mc_reset() stores it
> into the u8 in_device::mr_qrv, and the IGMPv3 retransmit counters filled
> from it (crcount, sf_crcount) are u8 as well. Anything above 255
> silently wraps. With 256, mr_qrv becomes 0, every
> "in_dev->mr_qrv ?: sysctl_igmp_qrv" falls back to 256, which truncates
> to 0 again in crcount, and igmpv3_send_cr() never puts the state change
> records for the group into a report. The older version querier present
> timeout (mr_qrv * mr_qi + mr_qri) also collapses to just mr_qri.
> 
> Make the sysctl a u8 like mr_qrv and switch to proc_dou8vec_minmax(),
> which rejects anything above 255, and document it.
> 
> Fixes: a9fe8e29945d ("ipv4: implement igmp_qrv sysctl to tune igmp 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>