[PATCH net v2 3/5] ipv6: restrict mld_qrv to 255

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

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@vger.kernel.org
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
v2: switched to u8 and proc_dou8vec_minmax(), as suggested by Kuniyuki
Iwashima.
---
 Documentation/networking/ip-sysctl.rst | 2 ++
 include/net/ipv6.h                     | 2 +-
 net/ipv6/mcast.c                       | 2 +-
 net/ipv6/sysctl_net_ipv6.c             | 4 ++--
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 4b19c8d3efda7..71f334f27004e 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2515,6 +2515,8 @@ mld_qrv - INTEGER
 
 	Minimum: 1 (as specified by RFC6636 4.5)
 
+	Maximum: 255
+
 max_dst_opts_number - INTEGER
 	Maximum number of non-padding TLVs allowed in a Destination
 	options extension header. If this value is less than zero
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 3de07e738538f..4901a92066e61 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -205,7 +205,7 @@ struct sk_buff *ip6_frag_next(struct sk_buff *skb,
 
 /* sysctls */
 extern int sysctl_mld_max_msf;
-extern int sysctl_mld_qrv;
+extern u8 sysctl_mld_qrv;
 
 #define _DEVINC(net, statname, mod, idev, field)			\
 ({									\
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index ecef55f261890..13f31132e0f97 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -106,7 +106,7 @@ static int __ipv6_dev_mc_inc(struct net_device *dev,
 #define IPV6_MLD_MAX_MSF	64
 
 int sysctl_mld_max_msf __read_mostly = IPV6_MLD_MAX_MSF;
-int sysctl_mld_qrv __read_mostly = MLD_QRV_DEFAULT;
+u8 sysctl_mld_qrv __read_mostly = MLD_QRV_DEFAULT;
 
 #define mc_assert_locked(idev)			\
 	lockdep_assert_held(&(idev)->mc_lock)
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index 1a0a36dcdabc1..f3ac04dbc71d0 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -226,9 +226,9 @@ static struct ctl_table ipv6_rotable[] = {
 	{
 		.procname	= "mld_qrv",
 		.data		= &sysctl_mld_qrv,
-		.maxlen		= sizeof(int),
+		.maxlen		= sizeof(u8),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
+		.proc_handler	= proc_dou8vec_minmax,
 		.extra1		= SYSCTL_ONE
 	},
 #ifdef CONFIG_NETLABEL
-- 
2.43.0