linux-kernel - Re: [PATCH 1/2] interconnect: Add character pointer initialization

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Message-ID: <2024083004-laptop-outrank-9710@gregkh>
Date: Fri, 30 Aug 2024 12:35:11 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Yibin Ding <Yibin.Ding@...soc.com>
Cc: djakov@...nel.org, rafael@...nel.org, yibin.ding01@...il.com,
	niuzhiguo84@...il.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Hao_hao.Wang@...soc.com,
	Ke.Wang@...soc.com
Subject: Re: [PATCH 1/2] interconnect: Add character pointer initialization

On Fri, Aug 30, 2024 at 06:22:44PM +0800, Yibin Ding wrote:
> From: Yibin Ding <Yibin.ding@...soc.com>
> 
> When accessing a node whose data type is a character pointer and has not
> been initialized, a crash will occur due to accessing a null pointer. So
> it is necessary to add the operation of initializing the character pointer.
> Since the debugfs_write_file_str() function performs a kfree() operation
> on the node data, memory is allocated to the node pointer during
> initialization will be released when data is written to the node.
> 
> Signed-off-by: Yibin Ding <Yibin.ding@...soc.com>
> ---
>  drivers/interconnect/debugfs-client.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/interconnect/debugfs-client.c b/drivers/interconnect/debugfs-client.c
> index bc3fd8a7b9eb..d62ba56b7bbe 100644
> --- a/drivers/interconnect/debugfs-client.c
> +++ b/drivers/interconnect/debugfs-client.c
> @@ -16,6 +16,7 @@
>  #undef INTERCONNECT_ALLOW_WRITE_DEBUGFS
>  
>  #if defined(INTERCONNECT_ALLOW_WRITE_DEBUGFS) && defined(CONFIG_DEBUG_FS)
> +#define INITNODE_SIZE 1

Why is this needed?  Why not just use the size of the structure?

>  
>  static LIST_HEAD(debugfs_paths);
>  static DEFINE_MUTEX(debugfs_lock);
> @@ -147,8 +148,13 @@ int icc_debugfs_client_init(struct dentry *icc_dir)
>  
>  	client_dir = debugfs_create_dir("test_client", icc_dir);
>  
> -	debugfs_create_str("src_node", 0600, client_dir, &src_node);
> -	debugfs_create_str("dst_node", 0600, client_dir, &dst_node);
> +	src_node = kzalloc(INITNODE_SIZE, GFP_KERNEL);
> +	dst_node = kzalloc(INITNODE_SIZE, GFP_KERNEL);

Wow, how did this ever work at all?

What commit id does this fix?

And where are you freeing this memory you just allocated?

thanks,

greg k-h