linux-kernel - Re: [PATCH v1] erofs: Fix state inconsistency when updating fsid/domain

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Message-ID: <3a0b7e98-5578-48f8-bcf2-8711a99adbc7@linux.alibaba.com>
Date: Tue, 6 Jan 2026 11:10:57 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Baolin Liu <liubaolin12138@....com>, xiang@...nel.org, chao@...nel.org
Cc: zbestahu@...il.com, jefflexu@...ux.alibaba.com, dhavale@...gle.com,
 lihongbo22@...wei.com, guochunhai@...o.com, linux-erofs@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, Baolin Liu <liubaolin@...inos.cn>
Subject: Re: [PATCH v1] erofs: Fix state inconsistency when updating
 fsid/domain_id

Hi Baolin,

On 2026/1/6 10:55, Baolin Liu wrote:
> From: Baolin Liu <liubaolin@...inos.cn>
> 
> When updating fsid or domain_id, the code frees the old pointer before
> allocating a new one. If allocation fails, the pointer becomes NULL
> while the old value is already freed, causing state inconsistency.
> 
> Fix by allocating the new value first, and only freeing the old value
> on success.
> 
> Signed-off-by: Baolin Liu <liubaolin@...inos.cn>
> ---
>   fs/erofs/super.c | 18 ++++++++++++------
>   1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 937a215f626c..6e083d7e634c 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -509,16 +509,22 @@ static int erofs_fc_parse_param(struct fs_context *fc,
>   		break;
>   #ifdef CONFIG_EROFS_FS_ONDEMAND
>   	case Opt_fsid:
> -		kfree(sbi->fsid);
> -		sbi->fsid = kstrdup(param->string, GFP_KERNEL);
> -		if (!sbi->fsid)
> +		char *new_fsid;

could you move

char *new_fsid, *new_domain_id;

to the beginning of `erofs_fc_parse_param()`
to avoid variable definitions in the switch statement?

or maybe just call it as:

char *newstr;

Thanks,
Gao Xiang

> +
> +		new_fsid = kstrdup(param->string, GFP_KERNEL);
> +		if (!new_fsid)
>   			return -ENOMEM;
> +		kfree(sbi->fsid);
> +		sbi->fsid = new_fsid;
>   		break;
>   	case Opt_domain_id:
> -		kfree(sbi->domain_id);
> -		sbi->domain_id = kstrdup(param->string, GFP_KERNEL);
> -		if (!sbi->domain_id)
> +		char *new_domain_id;
> +
> +		new_domain_id = kstrdup(param->string, GFP_KERNEL);
> +		if (!new_domain_id)
>   			return -ENOMEM;
> +		kfree(sbi->domain_id);
> +		sbi->domain_id = new_domain_id;
>   		break;
>   #else
>   	case Opt_fsid: