net/tls: Use RCU API to access tls_ctx->netdev

Currently, tls_device_down synchronizes with tls_device_resync_rx using
RCU, however, the pointer to netdev is stored using WRITE_ONCE and
loaded using READ_ONCE.

Although such approach is technically correct (rcu_dereference is
essentially a READ_ONCE, and rcu_assign_pointer uses WRITE_ONCE to store
NULL), using special RCU helpers for pointers is more valid, as it
includes additional checks and might change the implementation
transparently to the callers.

Mark the netdev pointer as __rcu and use the correct RCU helpers to
access it. For non-concurrent access pass the right conditions that
guarantee safe access (locks taken, refcount value). Also use the
correct helper in mlx5e, where even READ_ONCE was missing.

The transition to RCU exposes existing issues, fixed by this commit:

1. bond_tls_device_xmit could read netdev twice, and it could become
NULL the second time, after the NULL check passed.

2. Drivers shouldn't stop processing the last packet if tls_device_down
just set netdev to NULL, before tls_dev_del was called. This prevents a
possible packet drop when transitioning to the fallback software mode.

Fixes: 89df6a810470 ("net/bonding: Implement TLS TX device offload")
Fixes: c55dcdd435aa ("net/tls: Fix use-after-free after the TLS device goes down and up")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Link: https://lore.kernel.org/r/20220810081602.1435800-1-maximmi@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c
index 6b6c7044b64a..0aef69527226 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c
@@ -808,6 +808,7 @@ bool mlx5e_ktls_handle_tx_skb(struct net_device *netdev, struct mlx5e_txqsq *sq,
 {
 	struct mlx5e_ktls_offload_context_tx *priv_tx;
 	struct mlx5e_sq_stats *stats = sq->stats;
+	struct net_device *tls_netdev;
 	struct tls_context *tls_ctx;
 	int datalen;
 	u32 seq;
@@ -819,7 +820,12 @@ bool mlx5e_ktls_handle_tx_skb(struct net_device *netdev, struct mlx5e_txqsq *sq,
 	mlx5e_tx_mpwqe_ensure_complete(sq);
 
 	tls_ctx = tls_get_ctx(skb->sk);
-	if (WARN_ON_ONCE(tls_ctx->netdev != netdev))
+	tls_netdev = rcu_dereference_bh(tls_ctx->netdev);
+	/* Don't WARN on NULL: if tls_device_down is running in parallel,
+	 * netdev might become NULL, even if tls_is_sk_tx_device_offloaded was
+	 * true. Rather continue processing this packet.
+	 */
+	if (WARN_ON_ONCE(tls_netdev && tls_netdev != netdev))
 		goto err_out;
 
 	priv_tx = mlx5e_get_ktls_tx_priv_ctx(tls_ctx);