Subject: Re: [PATCH] [v2] net/mlx5e: fix a double-free in arfs_create_groups

From: Simon Horman <[email-masked]>
Date: Tue, 9 Jan 2024 08:18:37 +0000

On Mon, Jan 08, 2024 at 11:26:04PM +0800, Zhipeng Lu wrote:
> When `in` allocated by kvzalloc fails, arfs_create_groups will free
> ft->g and return an error. However, arfs_create_table, the only caller of
> arfs_create_groups, will hold this error and call to
> mlx5e_destroy_flow_table, in which the ft->g will be freed again.
> 
> Fixes: 1cabe6b0965e ("net/mlx5e: Create aRFS flow tables")
> Signed-off-by: Zhipeng Lu <[email-masked]>
> Reviewed-by: Simon Horman <[email-masked]>

When working on netdev (and probably elsewhere)
Please don't include Reviewed-by or other tags
that were explicitly supplied by someone: I don't recall
supplying the tag above so please drop it.

> ---
> Changelog:
> 
> v2: free ft->g just in arfs_create_groups with a unwind ladde.
> ---
>  .../net/ethernet/mellanox/mlx5/core/en_arfs.c   | 17 +++++++++--------
>  drivers/net/ethernet/mellanox/mlx5/core/en_fs.c |  1 -
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_arfs.c b/drivers/net/ethernet/mellanox/mlx5/core/en_arfs.c
> index bb7f86c993e5..c96f4c571b63 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_arfs.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_arfs.c
> @@ -252,13 +252,14 @@ static int arfs_create_groups(struct mlx5e_flow_table *ft,
>  	int err;
>  	u8 *mc;
>  
> +	ft->num_groups = 0;
> +

Although I suggested the above change, I think it
probably suitable for a separate patch. For one thing,
this is not mentioned in the patch subject. And for another,
it's probably better to change one thing at a time.

>  	ft->g = kcalloc(MLX5E_ARFS_NUM_GROUPS,
>  			sizeof(*ft->g), GFP_KERNEL);
>  	in = kvzalloc(inlen, GFP_KERNEL);
>  	if  (!in || !ft->g) {
> -		kfree(ft->g);
> -		kvfree(in);
> -		return -ENOMEM;
> +		err = -ENOMEM;
> +		goto free_ft;
>  	}

I would probably have split this up a bit:

>  
>  	mc = MLX5_ADDR_OF(create_flow_group_in, in, match_criteria);
> @@ -278,7 +279,7 @@ static int arfs_create_groups(struct mlx5e_flow_table *ft,
>  		break;
>  	default:
>  		err = -EINVAL;
> -		goto out;
> +		goto free_ft;
>  	}
>  
>  	switch (type) {
> @@ -300,7 +301,7 @@ static int arfs_create_groups(struct mlx5e_flow_table *ft,
>  		break;
>  	default:
>  		err = -EINVAL;
> -		goto out;
> +		goto free_ft;
>  	}
>  
>  	MLX5_SET_CFG(in, match_criteria_enable, MLX5_MATCH_OUTER_HEADERS);
> @@ -327,7 +328,9 @@ static int arfs_create_groups(struct mlx5e_flow_table *ft,
>  err:
>  	err = PTR_ERR(ft->g[ft->num_groups]);
>  	ft->g[ft->num_groups] = NULL;
> -out:
> +free_ft:
> +	kfree(ft->g);
> +	ft->g = NULL;
>  	kvfree(in);
>  
>  	return err;

I think that I would have named the labels err_*, which
I think is more idiomatic. So combined with my suggestion
above, I suggest something like:

-err:
+err_clean_group:
        err = PTR_ERR(ft->g[ft->num_groups]);
        ft->g[ft->num_groups] = NULL;
-out:
+err_free_in:
        kvfree(in);
+err_free_g:
+       kfree(ft->g);
+	ft->g = NULL;

 	return err;

> @@ -343,8 +346,6 @@ static int arfs_create_table(struct mlx5e_flow_steering *fs,
>  	struct mlx5_flow_table_attr ft_attr = {};
>  	int err;
>  
> -	ft->num_groups = 0;
> -
>  	ft_attr.max_fte = MLX5E_ARFS_TABLE_SIZE;
>  	ft_attr.level = MLX5E_ARFS_FT_LEVEL;
>  	ft_attr.prio = MLX5E_NIC_PRIO;
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_fs.c b/drivers/net/ethernet/mellanox/mlx5/core/en_fs.c
> index 777d311d44ef..7b6aa0c8b58d 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_fs.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_fs.c
> @@ -883,7 +883,6 @@ void mlx5e_fs_init_l2_addr(struct mlx5e_flow_steering *fs, struct net_device *ne
>  void mlx5e_destroy_flow_table(struct mlx5e_flow_table *ft)
>  {
>  	mlx5e_destroy_groups(ft);
> -	kfree(ft->g);
>  	mlx5_destroy_flow_table(ft->t);
>  	ft->t = NULL;

Is the above still needed in some cases, and safe in all cases?