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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , David Ahern , Ido Schimmel , Neal Cardwell , Joel Granados , Chia-Yu Chang , Fernando Fernandez Mancera , Wyatt Feng , Yung Chih Su , Flavio Leitner , Hannes Frederic Sowa , "Paul E. McKenney" , Petr Mladek , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Fri, 23 Oct 2026 17:13:29 +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, and every MLD retransmit counter derived > from it (mca_crcount, sf_crcount, mc_ifc_count, mc_dad_count) is u8 as > well. Anything above 255 silently wraps: 256 becomes 0, so no state > change report is ever retransmitted, and the first MLDv2 Query received > on the interface then trips the WARN_ON() in mld_update_qrv(): > > WARN_ON(idev->mc_qrv == 0); > > A plain bridge with mcast_querier enabled on the link is enough: > > 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: > > process_one_work+0x93a/0x1b20 > worker_thread+0x6d0/0x11d0 > kthread+0x358/0x470 > ret_from_fork+0x5b3/0x820 > ret_from_fork_asm+0x1a/0x30 > > > Cap the sysctl at U8_MAX, the largest value mc_qrv can actually hold. > > Fixes: 2f711939d2ea ("ipv6: add sysctl_mld_qrv to configure query robustness variable") > Cc: stable@vger.kernel.org > Signed-off-by: Jiayuan Chen > --- > net/ipv6/sysctl_net_ipv6.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c > index 1a0a36dcdabc..05a384680332 100644 > --- a/net/ipv6/sysctl_net_ipv6.c > +++ b/net/ipv6/sysctl_net_ipv6.c > @@ -29,6 +29,7 @@ static u32 rt6_multipath_hash_fields_all_mask = > FIB_MULTIPATH_HASH_FIELD_ALL_MASK; > static u32 ioam6_id_max = IOAM6_DEFAULT_ID; > static u64 ioam6_id_wide_max = IOAM6_DEFAULT_ID_WIDE; > +static int mld_qrv_max = U8_MAX; > > static int proc_rt6_multipath_hash_policy(const struct ctl_table *table, int write, > void *buffer, size_t *lenp, loff_t *ppos) > @@ -229,7 +230,8 @@ static struct ctl_table ipv6_rotable[] = { > .maxlen = sizeof(int), > .mode = 0644, > .proc_handler = proc_dointvec_minmax, inet6_dev.mc_qrv is u8, you can simply use proc_dou8vec_minmax() instead of adding extra2. > - .extra1 = SYSCTL_ONE > + .extra1 = SYSCTL_ONE, > + .extra2 = &mld_qrv_max, > }, > #ifdef CONFIG_NETLABEL > { > -- > 2.43.0 >