linux-kernel - [PATCH 3.16 370/370] sctp: deny peeloff operation on asocs with threads sleeping on it

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <lsq.1489146383.450701199@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:23 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Alexander Popov" <alex.popov@...ux.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Xin Long" <lucien.xin@...il.com>,
        "Marcelo Ricardo Leitner" <marcelo.leitner@...il.com>
Subject: [PATCH 3.16 370/370] sctp: deny peeloff operation on asocs with
 threads sleeping on it

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

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 <alex.popov@...ux.com>
Cc: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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;