Re: [PATCH v4] net: mlx5: Add a missing check on idr_find, free buf

[Eric Dumazet <eric.dumazet@gmail.com>]

On 03/19/2019 02:42 PM, Aditya Pakki wrote:
> idr_find() can return a NULL value to 'flow' which is used without a
> check. The patch adds a check to avoid potential NULL pointer dereference.
> 
> In case of mlx5_fpga_sbu_conn_sendmsg() failure, free buf allocated
> using kzalloc.
> 
> Fixes: ab412e1dd7db ("net/mlx5: Accel, add TLS rx offload routines")
> ---
> v3: Reorder buf allocations and flow check.
> v2: failure to return in case of flow failure.
> v1: Failed to free buf in case of flow failure.
> 
> Signed-off-by: Aditya Pakki <pakki001@umn.edu>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c b/drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c
> index 5cf5f2a9d51f..8de64e88c670 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/fpga/tls.c
> @@ -217,15 +217,21 @@ int mlx5_fpga_tls_resync_rx(struct mlx5_core_dev *mdev, u32 handle, u32 seq,
>  	void *cmd;
>  	int ret;
>  
> +	rcu_read_lock();
> +	flow = idr_find(&mdev->fpga->tls->rx_idr, ntohl(handle));
> +	rcu_read_unlock();

This looks suspect (even before your patch)

What prevents flow from disappearing after this rcu_read_lock() ?

IMO your patch might prevent a NULL deref, but not use-after-free.

> +
> +	if (!flow) {
> +		WARN_ONCE(1, "Received NULL pointer for handle\n");
> +		return -EINVAL;
> +	}
> +
>  	buf = kzalloc(size, GFP_ATOMIC);
>  	if (!buf)
>  		return -ENOMEM;
>  
>  	cmd = (buf + 1);
>  
> -	rcu_read_lock();
> -	flow = idr_find(&mdev->fpga->tls->rx_idr, ntohl(handle));
> -	rcu_read_unlock();
>  	mlx5_fpga_tls_flow_to_cmd(flow, cmd);
>  
>  	MLX5_SET(tls_cmd, cmd, swid, ntohl(handle));
> @@ -238,6 +244,8 @@ int mlx5_fpga_tls_resync_rx(struct mlx5_core_dev *mdev, u32 handle, u32 seq,
>  	buf->complete = mlx_tls_kfree_complete;
>  
>  	ret = mlx5_fpga_sbu_conn_sendmsg(mdev->fpga->tls->conn, buf);
> +	if (ret < 0)
> +		kfree(buf);
>  
>  	return ret;
>  }
>