net: rds: use maybe_get_net() when acquiring refcount on TCP sockets

Eric Dumazet is reporting addition on 0 problem at rds_tcp_tune(), for
delayed works queued in rds_wq might be invoked after a net namespace's
refcount already reached 0.

Since rds_tcp_exit_net() from cleanup_net() calls flush_workqueue(rds_wq),
it is guaranteed that we can instead use maybe_get_net() from delayed work
functions until rds_tcp_exit_net() returns.

Note that I'm not convinced that all works which might access a net
namespace are already queued in rds_wq by the moment rds_tcp_exit_net()
calls flush_workqueue(rds_wq). If some race is there, rds_tcp_exit_net()
will fail to wait for work functions, and kmem_cache_free() could be
called from net_free() before maybe_get_net() is called from
rds_tcp_tune().

Reported-by: Eric Dumazet <edumazet@google.com>
Fixes: 3a58f13a881ed351 ("net: rds: acquire refcount on TCP sockets")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/41d09faf-bc78-1a87-dfd1-c6d1b5984b61@I-love.SAKURA.ne.jp
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index 09cadd556d1e..7edf2e69d3fe 100644
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -133,7 +133,10 @@ int rds_tcp_accept_one(struct socket *sock)
 	__module_get(new_sock->ops->owner);
 
 	rds_tcp_keepalive(new_sock);
-	rds_tcp_tune(new_sock);
+	if (!rds_tcp_tune(new_sock)) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	inet = inet_sk(new_sock->sk);