tcp: fix possible deadlock in TCP stack vs BPF filter

Filtering the ACK packet was not put at the right place.

At this place, we already allocated a child and put it
into accept queue.

We absolutely need to call tcp_child_process() to release
its spinlock, or we will deadlock at accept() or close() time.

Found by syzkaller team (Thanks a lot !)

Fixes: 8fac365f63c8 ("tcp: Add a tcp_filter hook before handle ack packet")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Chenbo Feng <fengc@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 2521690d62d6..206210125fd7 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1456,6 +1456,8 @@ process:
                 }
                 sock_hold(sk);
                 refcounted = true;
+                if (tcp_filter(sk, skb))
+                        goto discard_and_relse;
                 nsk = tcp_check_req(sk, skb, req, false);
                 if (!nsk) {
                         reqsk_put(req);
@@ -1464,8 +1466,6 @@ process:
                 if (nsk == sk) {
                         reqsk_put(req);
                         tcp_v6_restore_cb(skb);
-                } else if (tcp_filter(sk, skb)) {
-                        goto discard_and_relse;
                 } else if (tcp_child_process(sk, nsk, skb)) {
                         tcp_v6_send_reset(nsk, skb);
                         goto discard_and_relse;