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

[Joas Antonio dos Santos <joasantonio108@gmail.com>]

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.

 drivers/net/ethernet/mellanox/mlx5/core/lib/macsec_fs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/macsec_fs.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/macsec_fs.c
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/macsec_fs.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/macsec_fs.c
@@ -94,6 +94,7 @@ struct mlx5_fs_id {
 	refcount_t refcnt;
 	sci_t sci;
 	struct rhash_head hash;
+	struct rcu_head rcu;
 };

 struct mlx5_macsec_device {
@@ -684,7 +685,7 @@ static void macsec_fs_id_del(struct list_head *macsec_devices_list, u32 fs_id,

 	xa_erase(fs_id_xa, fs_id);

-	kfree(fs_id_found);
+	kfree_rcu(fs_id_found, rcu);

 	if (macsec_fs_is_macsec_device_empty(macsec_device)) {
 		list_del(&macsec_device->macsec_devices_list_entry);
--
2.39.5