inet: fix races with reqsk timers

reqsk_queue_destroy() and reqsk_queue_unlink() should use
del_timer_sync() instead of del_timer() before calling reqsk_put(),
otherwise we could free a req still used by another cpu.

But before doing so, reqsk_queue_destroy() must release syn_wait_lock
spinlock or risk a dead lock, as reqsk_timer_handler() might
need to take this same spinlock from reqsk_queue_unlink() (called from
inet_csk_reqsk_queue_drop())

Fixes: fa76ce7328b2 ("inet: get rid of central tcp/dccp listener timer")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/request_sock.c b/net/core/request_sock.c
index 87b22c0..b42f0e2 100644 (file)
--- a/net/core/request_sock.c
+++ b/net/core/request_sock.c
@@ -103,10 +103,16 @@ void reqsk_queue_destroy(struct request_sock_queue *queue)
                        spin_lock_bh(&queue->syn_wait_lock);
                        while ((req = lopt->syn_table[i]) != NULL) {
                                lopt->syn_table[i] = req->dl_next;
+                               /* Because of following del_timer_sync(),
+                                * we must release the spinlock here
+                                * or risk a dead lock.
+                                */
+                               spin_unlock_bh(&queue->syn_wait_lock);
                                atomic_inc(&lopt->qlen_dec);
-                               if (del_timer(&req->rsk_timer))
+                               if (del_timer_sync(&req->rsk_timer))
                                        reqsk_put(req);
                                reqsk_put(req);
+                               spin_lock_bh(&queue->syn_wait_lock);
                        }
                        spin_unlock_bh(&queue->syn_wait_lock);
                }

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 60021d0..05e3145 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -593,7 +593,7 @@ static bool reqsk_queue_unlink(struct request_sock_queue *queue,
        }
 
        spin_unlock(&queue->syn_wait_lock);
-       if (del_timer(&req->rsk_timer))
+       if (del_timer_sync(&req->rsk_timer))
                reqsk_put(req);
        return found;
 }