From 6c24f53714319676adf7ab0d2d081e4b9de35bad Mon Sep 17 00:00:00 2001 From: Marcelo Ricardo Leitner Date: Thu, 23 Feb 2017 09:31:18 -0300 Subject: [PATCH] sctp: deny peeloff operation on asocs with threads sleeping on it 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 [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- net/sctp/socket.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/net/sctp/socket.c b/net/sctp/socket.c index ccbd6d08e773..93ea5ac2c7be 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -4242,6 +4242,12 @@ SCTP_STATIC int sctp_do_peeloff(struct sctp_association *asoc, struct sctp_af *af; int err = 0; + /* 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. */ @@ -6492,8 +6498,6 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, */ sctp_release_sock(sk); current_timeo = schedule_timeout(current_timeo); - if (sk != asoc->base.sk) - goto do_error; sctp_lock_sock(sk); *timeo_p = current_timeo; -- 2.39.2