inet: fix race in reqsk_queue_unlink()

reqsk_timer_handler() tests if icsk_accept_queue.listen_opt
is NULL at its beginning.

By the time it calls inet_csk_reqsk_queue_drop() and
reqsk_queue_unlink(), listener might have been closed and
inet_csk_listen_stop() had called reqsk_queue_yank_acceptq()
which sets icsk_accept_queue.listen_opt to NULL

We therefore need to correctly check listen_opt being NULL
after holding syn_wait_lock for proper synchronization.

Fixes: fa76ce7328b2 ("inet: get rid of central tcp/dccp listener timer")
Fixes: b357a364c57c ("inet: fix possible panic in reqsk_queue_unlink()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 7bb9c39e0a4d1a6a30b7aece9d3b0c17e447c20a..61b45a17fc738e17146a5e1f1cf97774f338179e 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -577,21 +577,22 @@ EXPORT_SYMBOL(inet_rtx_syn_ack);
 static bool reqsk_queue_unlink(struct request_sock_queue *queue,
                               struct request_sock *req)
 {
-       struct listen_sock *lopt = queue->listen_opt;
        struct request_sock **prev;
+       struct listen_sock *lopt;
        bool found = false;
 
        spin_lock(&queue->syn_wait_lock);
-
-       for (prev = &lopt->syn_table[req->rsk_hash]; *prev != NULL;
-            prev = &(*prev)->dl_next) {
-               if (*prev == req) {
-                       *prev = req->dl_next;
-                       found = true;
-                       break;
+       lopt = queue->listen_opt;
+       if (lopt) {
+               for (prev = &lopt->syn_table[req->rsk_hash]; *prev != NULL;
+                    prev = &(*prev)->dl_next) {
+                       if (*prev == req) {
+                               *prev = req->dl_next;
+                               found = true;
+                               break;
+                       }
                }
        }
-
        spin_unlock(&queue->syn_wait_lock);
        if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer))
                reqsk_put(req);