inetpeer: fix a race in inetpeer_gc_worker()

commit 5faa5df1fa2024 (inetpeer: Invalidate the inetpeer tree along with
the routing cache) added a race :

Before freeing an inetpeer, we must respect a RCU grace period, and make
sure no user will attempt to increase refcnt.

inetpeer_invalidate_tree() waits for a RCU grace period before inserting
inetpeer tree into gc_list and waking the worker. At that time, no
concurrent lookup can find a inetpeer in this tree.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 16 insertions, 5 deletions

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index b94765e38e80..2040bff945d4 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -40,7 +40,10 @@ struct inet_peer {
         u32                     pmtu_orig;
         u32                     pmtu_learned;
         struct inetpeer_addr_base redirect_learned;
-        struct list_head        gc_list;
+        union {
+                struct list_head        gc_list;
+                struct rcu_head     gc_rcu;
+        };
         /*
          * Once inet_peer is queued for deletion (refcnt == -1), following fields
          * are not available: rid, ip_id_count, tcp_ts, tcp_ts_stamp
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index d4d61b694fab..dfba343b2509 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -560,6 +560,17 @@ bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
 }
 EXPORT_SYMBOL(inet_peer_xrlim_allow);
 
+static void inetpeer_inval_rcu(struct rcu_head *head)
+{
+        struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
+
+        spin_lock_bh(&gc_lock);
+        list_add_tail(&p->gc_list, &gc_list);
+        spin_unlock_bh(&gc_lock);
+
+        schedule_delayed_work(&gc_work, gc_delay);
+}
+
 void inetpeer_invalidate_tree(int family)
 {
         struct inet_peer *old, *new, *prev;
@@ -576,10 +587,7 @@ void inetpeer_invalidate_tree(int family)
         prev = cmpxchg(&base->root, old, new);
         if (prev == old) {
                 base->total = 0;
-                spin_lock(&gc_lock);
-                list_add_tail(&prev->gc_list, &gc_list);
-                spin_unlock(&gc_lock);
-                schedule_delayed_work(&gc_work, gc_delay);
+                call_rcu(&prev->gc_rcu, inetpeer_inval_rcu);
         }
 
 out: