linux-kernel - Re: [PATCH v1] fs/super.c: Add NULL check for type in iterate_supers

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Message-ID: <20250403-inkognito-museen-4a78cc088344@brauner>
Date: Thu, 3 Apr 2025 10:01:29 +0200
From: Christian Brauner <brauner@...nel.org>
To: Xiaole He <hexiaole1994@....com>
Cc: viro@...iv.linux.org.uk, jack@...e.cz, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] fs/super.c: Add NULL check for type in
 iterate_supers_type

On Wed, Apr 02, 2025 at 11:45:29AM +0800, Xiaole He wrote:
> The first several lines of iterate_supers_type are below:
> 
> 1 void iterate_supers_type(struct file_system_type *type,
> 2 	void (*f)(struct super_block *, void *), void *arg)
> 3 {
> 4 	struct super_block *sb, *p = NULL;
> 5
> 6 	spin_lock(&sb_lock);
> 7 	hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
> 8 	...
> 9 }
> 
> The iterate_super_type is a exported symbol, and if iterate_supers_type
> is called with type of NULL, then there will be a NULL pointer
> dereference of argument type in line 7.
> 
> This patch fix above problem by adding NULL pointer check for argument
> type.
> 
> Signed-off-by: Xiaole He <hexiaole1994@....com>
> ---

Both Al and James already pointed out that this check is unnecessary and
ultimately misleading. So we're not going to accept this patch.