Re: [PATCH] mlxsw: core_env: Fix stack info leak in mlxsw_env_linecard_modules_power_mode_apply

[Ido Schimmel <idosch@nvidia.com>]

On Mon, Sep 01, 2025 at 11:10:19AM +0200, Petr Machata wrote:
> 
> Ido Schimmel <idosch@nvidia.com> writes:
> 
> > On Sat, Aug 30, 2025 at 04:11:22PM +0800, Miaoqian Lin wrote:
> >> The extack was declared on the stack without initialization.
> >> If mlxsw_env_set_module_power_mode_apply() fails to set extack,
> >> accessing extack._msg could leak information.
> >
> > Unless I'm missing something, I don't see a case where
> > mlxsw_env_set_module_power_mode_apply() returns an error without setting
> > extack. IOW, I don't see how this info leak can happen with existing
> > code.
> 
> Yeah, I agree it all looks initialized.
> 
> The patch still makes sense to me, it will make the code less prone to
> footguns in the future. The expectation with extack is that it's
> optional, though functions that take the argument typically also take
> care to set it (or propagate further). But here it is mandatory to
> initialize it, or else things break. With the patch we'd get a
> "(null)\n" instead of garbage. Not great, but better.

Can be solved with this diff:

diff --git a/drivers/net/ethernet/mellanox/mlxsw/core_env.c b/drivers/net/ethernet/mellanox/mlxsw/core_env.c
index 294e758f1067..8908520f39d9 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/core_env.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/core_env.c
@@ -1332,7 +1332,7 @@ mlxsw_env_linecard_modules_power_mode_apply(struct mlxsw_core *mlxsw_core,
 	for (i = 0; i < env->line_cards[slot_index]->module_count; i++) {
 		enum ethtool_module_power_mode_policy policy;
 		struct mlxsw_env_module_info *module_info;
-		struct netlink_ext_ack extack;
+		struct netlink_ext_ack extack = {};
 		int err;
 
 		module_info = &env->line_cards[slot_index]->module_info[i];
@@ -1340,7 +1340,7 @@ mlxsw_env_linecard_modules_power_mode_apply(struct mlxsw_core *mlxsw_core,
 		err = mlxsw_env_set_module_power_mode_apply(mlxsw_core,
 							    slot_index, i,
 							    policy, &extack);
-		if (err)
+		if (err && extack._msg)
 			dev_err(env->bus_info->dev, "%s\n", extack._msg);
 	}
 }