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


From: Sowmini Varadhan <sowmini.varad...@oracle.com>

commit f10b4cff98c6977668434fbf5dd58695eeca2897 upstream.

The rds_tcp_kill_sock() function parses the rds_tcp_conn_list
to find the rds_connection entries marked for deletion as part
of the netns deletion under the protection of the rds_tcp_conn_lock.
Since the rds_tcp_conn_list tracks rds_tcp_connections (which
have a 1:1 mapping with rds_conn_path), multiple tc entries in
the rds_tcp_conn_list will map to a single rds_connection, and will
be deleted as part of the rds_conn_destroy() operation that is
done outside the rds_tcp_conn_lock.

The rds_tcp_conn_list traversal done under the protection of
rds_tcp_conn_lock should not leave any doomed tc entries in
the list after the rds_tcp_conn_lock is released, else another
concurrently executiong netns delete (for a differnt netns) thread
may trip on these entries.

Reported-by: syzbot <syzkal...@googlegroups.com>
Signed-off-by: Sowmini Varadhan <sowmini.varad...@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilim...@oracle.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

 net/rds/tcp.c |    9 +++++++--
 net/rds/tcp.h |    1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -303,7 +303,8 @@ static void rds_tcp_conn_free(void *arg)
        rdsdebug("freeing tc %p\n", tc);
        spin_lock_irqsave(&rds_tcp_conn_lock, flags);
-       list_del(&tc->t_tcp_node);
+       if (!tc->t_tcp_node_detached)
+               list_del(&tc->t_tcp_node);
        spin_unlock_irqrestore(&rds_tcp_conn_lock, flags);
        kmem_cache_free(rds_tcp_conn_slab, tc);
@@ -528,8 +529,12 @@ static void rds_tcp_kill_sock(struct net
                if (net != c_net || !tc->t_sock)
-               if (!list_has_conn(&tmp_list, tc->t_cpath->cp_conn))
+               if (!list_has_conn(&tmp_list, tc->t_cpath->cp_conn)) {
                        list_move_tail(&tc->t_tcp_node, &tmp_list);
+               } else {
+                       list_del(&tc->t_tcp_node);
+                       tc->t_tcp_node_detached = true;
+               }
        list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node) {
--- a/net/rds/tcp.h
+++ b/net/rds/tcp.h
@@ -11,6 +11,7 @@ struct rds_tcp_incoming {
 struct rds_tcp_connection {
        struct list_head        t_tcp_node;
+       bool                    t_tcp_node_detached;
        struct rds_conn_path    *t_cpath;
        /* t_conn_path_lock synchronizes the connection establishment between
         * rds_tcp_accept_one and rds_tcp_conn_path_connect

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