linux-kernel - [PATCH 4.9 017/172] sctp: return next obj by passing pos + 1 into sctp_transport_get

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Date:   Mon,  3 Jul 2017 15:33:17 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xin Long <lucien.xin@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 017/172] sctp: return next obj by passing pos + 1 into sctp_transport_get_idx

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Xin Long <lucien.xin@...il.com>

[ Upstream commit 988c7322116970696211e902b468aefec95b6ec4 ]

In sctp_for_each_transport, pos is used to save how many objs it has
dumped. Now it gets the last obj by sctp_transport_get_idx, then gets
the next obj by sctp_transport_get_next.

The issue is that in the meanwhile if some objs in transport hashtable
are removed and the objs nums are less than pos, sctp_transport_get_idx
would return NULL and hti.walker.tbl is NULL as well. At this moment
it should stop hti, instead of continue getting the next obj. Or it
would cause a NULL pointer dereference in sctp_transport_get_next.

This patch is to pass pos + 1 into sctp_transport_get_idx to get the
next obj directly, even if pos > objs nums, it would return NULL and
stop hti.

Fixes: 626d16f50f39 ("sctp: export some apis or variables for sctp_diag and reuse some for proc")
Signed-off-by: Xin Long <lucien.xin@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sctp/socket.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4506,9 +4506,8 @@ int sctp_for_each_transport(int (*cb)(st
 	if (err)
 		return err;

-	sctp_transport_get_idx(net, &hti, pos);
-	obj = sctp_transport_get_next(net, &hti);
-	for (; obj && !IS_ERR(obj); obj = sctp_transport_get_next(net, &hti)) {
+	obj = sctp_transport_get_idx(net, &hti, pos + 1);
+	for (; !IS_ERR_OR_NULL(obj); obj = sctp_transport_get_next(net, &hti)) {
 		struct sctp_transport *transport = obj;

 		if (!sctp_transport_hold(transport))