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

[Fernando Fernandez Mancera]

On 10/23/26 11:13 AM, 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.
>
> Unlike MLD there is no WARN_ON() here, the reports just go missing.
>
> Cap the sysctl at U8_MAX, the largest value mr_qrv can actually hold.
>
> Fixes: a9fe8e29945d ("ipv4: implement igmp_qrv sysctl to tune igmp robustness variable")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>

Reviewed-by: Fernando Fernandez Mancera <fmancera@xxxxxxx>

Thanks!