Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936965AbdCJMcd (ORCPT ); Fri, 10 Mar 2017 07:32:33 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:45199 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936851AbdCJMTa (ORCPT ); Fri, 10 Mar 2017 07:19:30 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Alexander Popov" , "David S. Miller" , "Xin Long" , "Marcelo Ricardo Leitner" Date: Fri, 10 Mar 2017 11:46:23 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 370/370] sctp: deny peeloff operation on asocs with threads sleeping on it In-Reply-To: X-SA-Exim-Connect-IP: 82.70.136.246 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2323 Lines: 64 3.16.42-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Marcelo Ricardo Leitner commit dfcb9f4f99f1e9a49e43398a7bfbf56927544af1 upstream. commit 2dcab5984841 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf") attempted to avoid a BUG_ON call when the association being used for a sendmsg() is blocked waiting for more sndbuf and another thread did a peeloff operation on such asoc, moving it to another socket. As Ben Hutchings noticed, then in such case it would return without locking back the socket and would cause two unlocks in a row. Further analysis also revealed that it could allow a double free if the application managed to peeloff the asoc that is created during the sendmsg call, because then sctp_sendmsg() would try to free the asoc that was created only for that call. This patch takes another approach. It will deny the peeloff operation if there is a thread sleeping on the asoc, so this situation doesn't exist anymore. This avoids the issues described above and also honors the syscalls that are already being handled (it can be multiple sendmsg calls). Joint work with Xin Long. Fixes: 2dcab5984841 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf") Cc: Alexander Popov Cc: Ben Hutchings Signed-off-by: Marcelo Ricardo Leitner Signed-off-by: Xin Long Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/sctp/socket.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -4331,6 +4331,12 @@ int sctp_do_peeloff(struct sock *sk, sct if (!asoc) return -EINVAL; + /* If there is a thread waiting on more sndbuf space for + * sending on this asoc, it cannot be peeled. + */ + if (waitqueue_active(&asoc->wait)) + return -EBUSY; + /* An association cannot be branched off from an already peeled-off * socket, nor is this supported for tcp style sockets. */ @@ -6760,8 +6766,6 @@ static int sctp_wait_for_sndbuf(struct s */ release_sock(sk); current_timeo = schedule_timeout(current_timeo); - if (sk != asoc->base.sk) - goto do_error; lock_sock(sk); *timeo_p = current_timeo;