netfilter: qtaguid: initialize a local var to keep compiler happy.

There was a case that might have seemed like new_tag_stat was not
initialized and actually used.
Added comment explaining why it was impossible, and a BUG()
in case the logic gets changed.

Change-Id: I1eddd1b6f754c08a3bf89f7e9427e5dce1dfb081
Signed-off-by: JP Abgrall <jpa@google.com>

diff --git a/net/netfilter/xt_qtaguid.c b/net/netfilter/xt_qtaguid.c
index 08086d680c2c2b6c5ec668c704f500ae00b5ff9d..0166d340d5c9b74dc60598531f62564027e7ba2b 100644 (file)
--- a/net/netfilter/xt_qtaguid.c
+++ b/net/netfilter/xt_qtaguid.c
@@ -1265,7 +1265,7 @@ static void if_tag_stat_update(const char *ifname, uid_t uid,
        struct data_counters *uid_tag_counters;
        struct sock_tag *sock_tag_entry;
        struct iface_stat *iface_entry;
-       struct tag_stat *new_tag_stat;
+       struct tag_stat *new_tag_stat = NULL;
        MT_DEBUG("qtaguid: if_tag_stat_update(ifname=%s "
                "uid=%u sk=%p dir=%d proto=%d bytes=%d)\n",
                 ifname, uid, sk, direction, proto, bytes);
@@ -1330,8 +1330,19 @@ static void if_tag_stat_update(const char *ifname, uid_t uid,
        }
 
        if (acct_tag) {
+               /* Create the child {acct_tag, uid_tag} and hook up parent. */
                new_tag_stat = create_if_tag_stat(iface_entry, tag);
                new_tag_stat->parent_counters = uid_tag_counters;
+       } else {
+               /*
+                * For new_tag_stat to be still NULL here would require:
+                *  {0, uid_tag} exists
+                *  and {acct_tag, uid_tag} doesn't exist
+                *  AND acct_tag == 0.
+                * Impossible. This reassures us that new_tag_stat
+                * below will always be assigned.
+                */
+               BUG_ON(!new_tag_stat);
        }
        tag_stat_update(new_tag_stat, direction, proto, bytes);
        spin_unlock_bh(&iface_entry->tag_stat_list_lock);