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

[Paolo Abeni <pabeni@redhat.com>]

On 11/4/26 13:49, Tariq Toukan wrote:
> 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>

While I have your attention, there is another mlx patch pending:

https://lore.kernel.org/all/20261028145805.54595-3-fourier.thomas@gmail.com/

/P