genetlink: fix genlmsg_multicast() bug

Unfortunately, I introduced a tremendously stupid bug into
genlmsg_multicast() when doing all those multicast group
changes: it adjusts the group number, but then passes it
to genlmsg_multicast_netns() which does that again.

Somehow, my tests failed to catch this, so add a warning
into genlmsg_multicast_netns() and remove the offending
group ID adjustment.

Also add a warning to the similar code in other functions
so people who misuse them are more loudly warned.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 3 insertions, 6 deletions

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index ace4abf118d7..771af09e90eb 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -265,7 +265,7 @@ static inline int genlmsg_multicast_netns(struct genl_family *family,
                                           struct net *net, struct sk_buff *skb,
                                           u32 portid, unsigned int group, gfp_t flags)
 {
-        if (group >= family->n_mcgrps)
+        if (WARN_ON_ONCE(group >= family->n_mcgrps))
                 return -EINVAL;
         group = family->mcgrp_offset + group;
         return nlmsg_multicast(net->genl_sock, skb, portid, group, flags);
@@ -283,9 +283,6 @@ static inline int genlmsg_multicast(struct genl_family *family,
                                     struct sk_buff *skb, u32 portid,
                                     unsigned int group, gfp_t flags)
 {
-        if (group >= family->n_mcgrps)
-                return -EINVAL;
-        group = family->mcgrp_offset + group;
         return genlmsg_multicast_netns(family, &init_net, skb,
                                        portid, group, flags);
 }
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 7dbc4f732c75..4518a57aa5fe 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -1045,7 +1045,7 @@ static int genlmsg_mcast(struct sk_buff *skb, u32 portid, unsigned long group,
 int genlmsg_multicast_allns(struct genl_family *family, struct sk_buff *skb,
                             u32 portid, unsigned int group, gfp_t flags)
 {
-        if (group >= family->n_mcgrps)
+        if (WARN_ON_ONCE(group >= family->n_mcgrps))
                 return -EINVAL;
         group = family->mcgrp_offset + group;
         return genlmsg_mcast(skb, portid, group, flags);
@@ -1062,7 +1062,7 @@ void genl_notify(struct genl_family *family,
         if (nlh)
                 report = nlmsg_report(nlh);
 
-        if (group >= family->n_mcgrps)
+        if (WARN_ON_ONCE(group >= family->n_mcgrps))
                 return;
         group = family->mcgrp_offset + group;
         nlmsg_notify(sk, skb, portid, group, report, flags);