netdev - [PATCH net-next 3/3] rds: tcp: atomically purge entries from rds_tcp_conn

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Date:   Thu, 30 Nov 2017 11:11:29 -0800
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, rds-devel@....oracle.com,
        sowmini.varadhan@...cle.com, santosh.shilimkar@...cle.com
Subject: [PATCH net-next 3/3] rds: tcp: atomically purge entries from rds_tcp_conn_list during netns delete

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 <syzkaller@...glegroups.com>
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
---
 net/rds/tcp.c |    9 +++++++--
 net/rds/tcp.h |    1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index f580f72..39f502d 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -306,7 +306,8 @@ 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);
@@ -510,8 +511,12 @@ static void rds_tcp_kill_sock(struct net *net)
 
 		if (net != c_net || !tc->t_sock)
 			continue;
-		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;
+		}
 	}
 	spin_unlock_irq(&rds_tcp_conn_lock);
 	list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node)
diff --git a/net/rds/tcp.h b/net/rds/tcp.h
index f8800b7..8775349 100644
--- 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
-- 
1.7.1