net: bridge: mcast: add and enforce query interval minimum

As reported[1] if query interval is set too low and we have multiple
bridges or even a single bridge with multiple querier vlans configured
we can crash the machine. Add a 1 second minimum which must be enforced
by overwriting the value if set lower (i.e. without returning an error) to
avoid breaking user-space. If that happens a log message is emitted to let
the administrator know that the interval has been set to the minimum.
The issue has been present since these intervals could be user-controlled.

[1] https://lore.kernel.org/netdev/e8b9ce41-57b9-b6e2-a46a-ff9c791cf0ba@gmail.com/

Fixes: d902eee4 ("bridge: Add multicast count/interval sysfs entries")
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/bridge/br_multicast.c

@@ -4522,6 +4522,22 @@ int br_multicast_set_mld_version(struct net_bridge_mcast *brmctx,
 }
 #endif
 
+void br_multicast_set_query_intvl(struct net_bridge_mcast *brmctx,
+				  unsigned long val)
+{
+	unsigned long intvl_jiffies = clock_t_to_jiffies(val);
+
+	if (intvl_jiffies < BR_MULTICAST_QUERY_INTVL_MIN) {
+		br_info(brmctx->br,
+			"trying to set multicast query interval below minimum, setting to %lu (%ums)\n",
+			jiffies_to_clock_t(BR_MULTICAST_QUERY_INTVL_MIN),
+			jiffies_to_msecs(BR_MULTICAST_QUERY_INTVL_MIN));
+		intvl_jiffies = BR_MULTICAST_QUERY_INTVL_MIN;
+	}
+
+	brmctx->multicast_query_interval = intvl_jiffies;
+}
+
 /**
  * br_multicast_list_adjacent - Returns snooped multicast addresses
  * @dev:	The bridge port adjacent to which to retrieve addresses

net/bridge/br_netlink.c

@@ -1357,7 +1357,7 @@ static int br_changelink(struct net_device *brdev, struct nlattr *tb[],
 	if (data[IFLA_BR_MCAST_QUERY_INTVL]) {
 		u64 val = nla_get_u64(data[IFLA_BR_MCAST_QUERY_INTVL]);
 
-		br->multicast_ctx.multicast_query_interval = clock_t_to_jiffies(val);
+		br_multicast_set_query_intvl(&br->multicast_ctx, val);
 	}
 
 	if (data[IFLA_BR_MCAST_QUERY_RESPONSE_INTVL]) {

net/bridge/br_private.h

@@ -28,6 +28,7 @@
 #define BR_MAX_PORTS	(1<<BR_PORT_BITS)
 
 #define BR_MULTICAST_DEFAULT_HASH_MAX 4096
+#define BR_MULTICAST_QUERY_INTVL_MIN msecs_to_jiffies(1000)
 
 #define BR_HWDOM_MAX BITS_PER_LONG
 
@@ -963,6 +964,8 @@ int br_multicast_dump_querier_state(struct sk_buff *skb,
 				    int nest_attr);
 size_t br_multicast_querier_state_size(void);
 size_t br_rports_size(const struct net_bridge_mcast *brmctx);
+void br_multicast_set_query_intvl(struct net_bridge_mcast *brmctx,
+				  unsigned long val);
 
 static inline bool br_group_is_l2(const struct br_ip *group)
 {

net/bridge/br_sysfs_br.c

@@ -658,7 +658,7 @@ static ssize_t multicast_query_interval_show(struct device *d,
 static int set_query_interval(struct net_bridge *br, unsigned long val,
 			      struct netlink_ext_ack *extack)
 {
-	br->multicast_ctx.multicast_query_interval = clock_t_to_jiffies(val);
+	br_multicast_set_query_intvl(&br->multicast_ctx, val);
 	return 0;
 }
 

net/bridge/br_vlan_options.c

@@ -521,7 +521,7 @@ static int br_vlan_process_global_one_opts(const struct net_bridge *br,
 		u64 val;
 
 		val = nla_get_u64(tb[BRIDGE_VLANDB_GOPTS_MCAST_QUERY_INTVL]);
-		v->br_mcast_ctx.multicast_query_interval = clock_t_to_jiffies(val);
+		br_multicast_set_query_intvl(&v->br_mcast_ctx, val);
 		*changed = true;
 	}
 	if (tb[BRIDGE_VLANDB_GOPTS_MCAST_QUERY_RESPONSE_INTVL]) {