sctp: hold transport before accessing its asoc in sctp_transport_get_next

[ Upstream commit bab1be79a5169ac748d8292b20c86d874022d7ba ]

As Marcelo noticed, in sctp_transport_get_next, it is iterating over
transports but then also accessing the association directly, without
checking any refcnts before that, which can cause an use-after-free
Read.

So fix it by holding transport before accessing the association. With
that, sctp_transport_hold calls can be removed in the later places.

Fixes: 626d16f50f39 ("sctp: export some apis or variables for sctp_diag and reuse some for proc")
Reported-by: syzbot+fe62a0c9aa6a85c6de16@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sctp/proc.c b/net/sctp/proc.c
index 206377fe91ec4db4a59b24bf45daa0e42be0015b..fd7f23566ed6bf35218fe46a360b4137be72cbf9 100644 (file)
--- a/net/sctp/proc.c
+++ b/net/sctp/proc.c
@@ -337,8 +337,6 @@ static int sctp_assocs_seq_show(struct seq_file *seq, void *v)
        }
 
        transport = (struct sctp_transport *)v;
-       if (!sctp_transport_hold(transport))
-               return 0;
        assoc = transport->asoc;
        epb = &assoc->base;
        sk = epb->sk;
@@ -428,8 +426,6 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
        }
 
        transport = (struct sctp_transport *)v;
-       if (!sctp_transport_hold(transport))
-               return 0;
        assoc = transport->asoc;
 
        list_for_each_entry_rcu(tsp, &assoc->peer.transport_addr_list,

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 78f38056fca6dc0cb32ad050940ace584735e07f..64d2d9ea2f8c8a4f91aed862696c7f0fa181336a 100644 (file)
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4476,9 +4476,14 @@ struct sctp_transport *sctp_transport_get_next(struct net *net,
                        break;
                }
 
+               if (!sctp_transport_hold(t))
+                       continue;
+
                if (net_eq(sock_net(t->asoc->base.sk), net) &&
                    t->asoc->peer.primary_path == t)
                        break;
+
+               sctp_transport_put(t);
        }
 
        return t;
@@ -4488,13 +4493,18 @@ struct sctp_transport *sctp_transport_get_idx(struct net *net,
                                              struct rhashtable_iter *iter,
                                              int pos)
 {
-       void *obj = SEQ_START_TOKEN;
+       struct sctp_transport *t;
 
-       while (pos && (obj = sctp_transport_get_next(net, iter)) &&
-              !IS_ERR(obj))
-               pos--;
+       if (!pos)
+               return SEQ_START_TOKEN;
 
-       return obj;
+       while ((t = sctp_transport_get_next(net, iter)) && !IS_ERR(t)) {
+               if (!--pos)
+                       break;
+               sctp_transport_put(t);
+       }
+
+       return t;
 }
 
 int sctp_for_each_endpoint(int (*cb)(struct sctp_endpoint *, void *),
@@ -4556,8 +4566,6 @@ int sctp_for_each_transport(int (*cb)(struct sctp_transport *, void *),
        for (; !IS_ERR_OR_NULL(obj); obj = sctp_transport_get_next(net, &hti)) {
                struct sctp_transport *transport = obj;
 
-               if (!sctp_transport_hold(transport))
-                       continue;
                err = cb(transport, p);
                sctp_transport_put(transport);
                if (err)