net/mlx5: lag: Check for LAG device before creating debugfs

__mlx5_lag_dev_add_mdev() may return 0 (success) even when an error
occurs that is handled gracefully. Consequently, the initialization
flow proceeds to call mlx5_ldev_add_debugfs() even when there is no
valid LAG context.

mlx5_ldev_add_debugfs() blindly created the debugfs directory and
attributes. This exposed interfaces (like the members file) that rely on
a valid ldev pointer, leading to potential NULL pointer dereferences if
accessed when ldev is NULL.

Add a check to verify that mlx5_lag_dev(dev) returns a valid pointer
before attempting to create the debugfs entries.

Fixes: 7f46a0b ("net/mlx5: Lag, add debugfs to query hardware lag state")
Signed-off-by: Shay Drory <[email protected]>
Reviewed-by: Mark Bloch <[email protected]>
Signed-off-by: Tariq Toukan <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: shayshyi

drivers/net/ethernet/mellanox/mlx5/core/lag/debugfs.c

@@ -160,8 +160,11 @@ DEFINE_SHOW_ATTRIBUTE(members);
 
 void mlx5_ldev_add_debugfs(struct mlx5_core_dev *dev)
 {
+	struct mlx5_lag *ldev = mlx5_lag_dev(dev);
 	struct dentry *dbg;
 
+	if (!ldev)
+		return;
 	dbg = debugfs_create_dir("lag", mlx5_debugfs_get_dev_root(dev));
 	dev->priv.dbg.lag_debugfs = dbg;