Re: [PATCH net v2] net/mlx5: macsec: free struct mlx5_fs_id after an RCU grace period

[Simon Horman <horms@kernel.org>]

On Tue, Oct 27, 2026 at 06:17:06PM -0300, Joas Antonio dos Santos wrote:
> macsec_fs_id_del() removes a struct mlx5_fs_id from its rhashtable with
> rhashtable_remove_fast() and then frees it with kfree() right away.
> 
> The TX (SCI) table is read locklessly from the transmit path:
> mlx5e_macsec_handle_tx_skb() and mlx5e_macsec_tx_build_eseg() call
> mlx5_macsec_fs_get_fs_id_from_hashtable(), which does
> rhashtable_lookup() under rcu_read_lock() and then reads
> mlx5_fs_id->id. A transmit that looked the entry up just before it was
> removed reads freed memory.
> 
> Before commit d4ece08f4b1d ("net/mlx5: Maintain fs_id xarray per MACsec
> device inside macsec steering") the SCI table held struct
> mlx5e_macsec_sa directly, and mlx5e_macsec_del_txsa() freed it with
> kfree_rcu_mightsleep(). That commit moved the table into macsec_fs.c
> with the new struct mlx5_fs_id, but frees it with a plain kfree().
> 
> Add an rcu_head to struct mlx5_fs_id and free it with kfree_rcu().
> 
> The same issue was flagged by the Sashiko AI review as a pre-existing
> problem while reviewing the HW-GRO for PSP series.
> 
> Fixes: d4ece08f4b1d ("net/mlx5: Maintain fs_id xarray per MACsec device inside macsec steering")
> Link: https://lore.kernel.org/all/20260909065542.4B80D1F00ACA@smtp.kernel.org/
> Signed-off-by: Joas Antonio dos Santos <joasantonio108@gmail.com>
> Assisted-by: Yaga Agent HackerSec Claude:claude-opus-5-5
> ---
> v2:
> - Drop the macsec.c hunk: the sc_xarray_element free was already fixed
>   by ad17ad50b8dc ("net: mlx5e: Fix use-after-free of the MACsec xarray
>   entry on RX SC deletion"). (Simon)
> - Embed an rcu_head and use kfree_rcu() instead of
>   kvfree_rcu_mightsleep(). (Simon)
> - Fixes: now points at the commit that introduced the kfree().
> - v1: https://lore.kernel.org/all/179285888829.90275.17386097105525068016@gmail.com/
> 
> Testing: compile-tested only (arm64, W=1, CONFIG_MLX5_MACSEC=y, no new
> warnings). I do not have
> MACsec-capable ConnectX hardware, so this was not run on a device.

Thanks for the update, and testing and discovery information.

Reviewed-by: Simon Horman <horms@kernel.org>