[PATCH v1] erofs: Fix state inconsistency when updating fsid/domain_id

[Hongbo Li]

Hi,

On 2026/1/6 10:55, Baolin Liu wrote:
> From: Baolin Liu <liubaolin at kylinos.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 at kylinos.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;
> +
> +		new_fsid = kstrdup(param->string, GFP_KERNEL);

May be there is no need to keep the old pointer. Because
1) The fsid/domain_id is ignored in reconfiguration.
2) Even if memory allocation fails when the user first mounts with multi 
fsid/domain_id options (like -o fsid=xxx1,fsid=xxx2), the old fsid 
pointer would also need to be released in cleanup procedure.

so am I right?

Thanks,
Hongbo

> +		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: