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

[Tariq Toukan <tariqt@nvidia.com>]

On 04/11/2026 13:20, Cosmin Ratiu wrote:
> On Tue, 2026-10-27 at 18:17 -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.
>>
>>   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
> 
> Thank you for the fix, it looks good.
> 
> Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>

Acked-by: Tariq Toukan <tariqt@nvidia.com>