From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Fastabend Subject: [bpf PATCH] bpf: sockmap missing NULL psock check Date: Tue, 02 Jan 2018 19:47:05 -0800 Message-ID: <20180103034705.11636.98766.stgit@john-Precision-Tower-5810> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: borkmann@iogearbox.net, alexei.starovoitov@gmail.com Return-path: Received: from mail-pl0-f68.google.com ([209.85.160.68]:40690 "EHLO mail-pl0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750865AbeACDrQ (ORCPT ); Tue, 2 Jan 2018 22:47:16 -0500 Received: by mail-pl0-f68.google.com with SMTP id 62so442452pld.7 for ; Tue, 02 Jan 2018 19:47:15 -0800 (PST) Sender: netdev-owner@vger.kernel.org List-ID: Add psock NULL check to handle a racing sock event that can get the sk_callback_lock before this case but after xchg happens causing the refcnt to hit zero and sock user data (psock) to be null and queued for garbage collection. Also add a comment in the code because this is a bit subtle and not obvious in my opinion. Signed-off-by: John Fastabend --- kernel/bpf/sockmap.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c index 5ee2e41..dfbbde2 100644 --- a/kernel/bpf/sockmap.c +++ b/kernel/bpf/sockmap.c @@ -591,6 +591,13 @@ static void sock_map_free(struct bpf_map *map) write_lock_bh(&sock->sk_callback_lock); psock = smap_psock_sk(sock); + /* This check handles a racing sock event that can get the + * sk_callback_lock before this case but after xchg happens + * causing the refcnt to hit zero and sock user data (psock) + * to be null and queued for garbage collection. + */ + if (unlikely(!psock)) + continue; smap_list_remove(psock, &stab->sock_map[i]); smap_release_sock(psock, sock); write_unlock_bh(&sock->sk_callback_lock);