[PATCH net v2 4/5] ipv4: restrict igmp_qrv to 255

[Jiayuan Chen <jiayuan.chen@linux.dev>]

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@vger.kernel.org
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
For AI review: drivers/net/amt.c writing sysctl_igmp_qrv into the 3-bit
qrv wire fields is pre-existing and out of scope for this patch.

v2: switched to u8 and proc_dou8vec_minmax(), as suggested by Kuniyuki
Iwashima.
---
 Documentation/networking/ip-sysctl.rst                        | 2 ++
 Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst | 2 +-
 include/net/netns/ipv4.h                                      | 2 +-
 net/ipv4/sysctl_net_ipv4.c                                    | 4 ++--
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 71f334f27004e..9e282fb046904 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1906,6 +1906,8 @@ igmp_qrv - INTEGER
 
 	Minimum: 1 (as specified by RFC6636 4.5)
 
+	Maximum: 255
+
 force_igmp_version - INTEGER
 	- 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback
 	  allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier
diff --git a/Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst b/Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst
index 3dc03bff739e4..2833ce6cba1d4 100644
--- a/Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst
+++ b/Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst
@@ -143,9 +143,9 @@ int                             sysctl_udp_rmem_min
 u8                              sysctl_fib_notify_on_flag_change
 u8                              sysctl_udp_l3mdev_accept
 u8                              sysctl_igmp_llm_reports
+u8                              sysctl_igmp_qrv
 int                             sysctl_igmp_max_memberships
 int                             sysctl_igmp_max_msf
-int                             sysctl_igmp_qrv
 struct_ping_group_range         ping_group_range
 atomic_t                        dev_addr_genid
 unsigned_int                    sysctl_udp_child_hash_entries
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index cb7f8bf15671c..3efbc7f4b4f7d 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -258,9 +258,9 @@ struct netns_ipv4 {
 #endif
 
 	u8 sysctl_igmp_llm_reports;
+	u8 sysctl_igmp_qrv;
 	int sysctl_igmp_max_memberships;
 	int sysctl_igmp_max_msf;
-	int sysctl_igmp_qrv;
 
 	struct ping_group_range ping_group_range;
 	u16			ping_port_rover;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index e3760daa34706..09f7fc6771456 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -975,9 +975,9 @@ static const struct ctl_table ipv4_net_table[] = {
 	{
 		.procname	= "igmp_qrv",
 		.data		= &init_net.ipv4.sysctl_igmp_qrv,
-		.maxlen		= sizeof(int),
+		.maxlen		= sizeof(u8),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
+		.proc_handler	= proc_dou8vec_minmax,
 		.extra1		= SYSCTL_ONE
 	},
 #endif
-- 
2.43.0