igmp: Fix data-races around sysctl_igmp_llm_reports.

While reading sysctl_igmp_llm_reports, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its readers.

This test can be packed into a helper, so such changes will be in the
follow-up series after net is merged into net-next.

  if (ipv4_is_local_multicast(pmc->multiaddr) &&
      !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))

Fixes: df2cf4a78e48 ("IGMP: Inhibit reports for local multicast groups")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index b65d074..cf75fff 100644 (file)
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -467,7 +467,8 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ip_mc_list *pmc,
 
        if (pmc->multiaddr == IGMP_ALL_HOSTS)
                return skb;
-       if (ipv4_is_local_multicast(pmc->multiaddr) && !net->ipv4.sysctl_igmp_llm_reports)
+       if (ipv4_is_local_multicast(pmc->multiaddr) &&
+           !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                return skb;
 
        mtu = READ_ONCE(dev->mtu);
@@ -593,7 +594,7 @@ static int igmpv3_send_report(struct in_device *in_dev, struct ip_mc_list *pmc)
                        if (pmc->multiaddr == IGMP_ALL_HOSTS)
                                continue;
                        if (ipv4_is_local_multicast(pmc->multiaddr) &&
-                            !net->ipv4.sysctl_igmp_llm_reports)
+                           !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                                continue;
                        spin_lock_bh(&pmc->lock);
                        if (pmc->sfcount[MCAST_EXCLUDE])
@@ -736,7 +737,8 @@ static int igmp_send_report(struct in_device *in_dev, struct ip_mc_list *pmc,
        if (type == IGMPV3_HOST_MEMBERSHIP_REPORT)
                return igmpv3_send_report(in_dev, pmc);
 
-       if (ipv4_is_local_multicast(group) && !net->ipv4.sysctl_igmp_llm_reports)
+       if (ipv4_is_local_multicast(group) &&
+           !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                return 0;
 
        if (type == IGMP_HOST_LEAVE_MESSAGE)
@@ -920,7 +922,8 @@ static bool igmp_heard_report(struct in_device *in_dev, __be32 group)
 
        if (group == IGMP_ALL_HOSTS)
                return false;
-       if (ipv4_is_local_multicast(group) && !net->ipv4.sysctl_igmp_llm_reports)
+       if (ipv4_is_local_multicast(group) &&
+           !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                return false;
 
        rcu_read_lock();
@@ -1045,7 +1048,7 @@ static bool igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
                if (im->multiaddr == IGMP_ALL_HOSTS)
                        continue;
                if (ipv4_is_local_multicast(im->multiaddr) &&
-                   !net->ipv4.sysctl_igmp_llm_reports)
+                   !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                        continue;
                spin_lock_bh(&im->lock);
                if (im->tm_running)
@@ -1296,7 +1299,8 @@ static void __igmp_group_dropped(struct ip_mc_list *im, gfp_t gfp)
 #ifdef CONFIG_IP_MULTICAST
        if (im->multiaddr == IGMP_ALL_HOSTS)
                return;
-       if (ipv4_is_local_multicast(im->multiaddr) && !net->ipv4.sysctl_igmp_llm_reports)
+       if (ipv4_is_local_multicast(im->multiaddr) &&
+           !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                return;
 
        reporter = im->reporter;
@@ -1338,7 +1342,8 @@ static void igmp_group_added(struct ip_mc_list *im)
 #ifdef CONFIG_IP_MULTICAST
        if (im->multiaddr == IGMP_ALL_HOSTS)
                return;
-       if (ipv4_is_local_multicast(im->multiaddr) && !net->ipv4.sysctl_igmp_llm_reports)
+       if (ipv4_is_local_multicast(im->multiaddr) &&
+           !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                return;
 
        if (in_dev->dead)
@@ -1642,7 +1647,7 @@ static void ip_mc_rejoin_groups(struct in_device *in_dev)
                if (im->multiaddr == IGMP_ALL_HOSTS)
                        continue;
                if (ipv4_is_local_multicast(im->multiaddr) &&
-                   !net->ipv4.sysctl_igmp_llm_reports)
+                   !READ_ONCE(net->ipv4.sysctl_igmp_llm_reports))
                        continue;
 
                /* a failover is happening and switches