RDS: have sockets get transport module references

Right now there's nothing to stop the various paths that use
rs->rs_transport from racing with rmmod and executing freed transport
code.  The simple fix is to have binding to a transport also hold a
reference to the transport's module, removing this class of races.

We already had an unused t_owner field which was set for the modular
transports and which wasn't set for the built-in loop transport.

Signed-off-by: Zach Brown <zach.brown@oracle.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/net/rds/transport.c b/net/rds/transport.c
index 7e1067901353..7f2ac4fec367 100644
--- a/net/rds/transport.c
+++ b/net/rds/transport.c
@@ -71,19 +71,28 @@ void rds_trans_unregister(struct rds_transport *trans)
 }
 EXPORT_SYMBOL_GPL(rds_trans_unregister);
 
+void rds_trans_put(struct rds_transport *trans)
+{
+        if (trans && trans->t_owner)
+                module_put(trans->t_owner);
+}
+
 struct rds_transport *rds_trans_get_preferred(__be32 addr)
 {
         struct rds_transport *ret = NULL;
-        int i;
+        struct rds_transport *trans;
+        unsigned int i;
 
         if (IN_LOOPBACK(ntohl(addr)))
                 return &rds_loop_transport;
 
         down_read(&rds_trans_sem);
-        for (i = 0; i < RDS_TRANS_COUNT; i++)
-        {
-                if (transports[i] && (transports[i]->laddr_check(addr) == 0)) {
-                        ret = transports[i];
+        for (i = 0; i < RDS_TRANS_COUNT; i++) {
+                trans = transports[i];
+
+                if (trans && (trans->laddr_check(addr) == 0) &&
+                    (!trans->t_owner || try_module_get(trans->t_owner))) {
+                        ret = trans;
                         break;
                 }
         }