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

[liubaolin]

> Dear Hongbo Li,
> 
> I have reviewed this carefully, and I agree with your point. The old value will eventually be freed in erofs_sb_free(), and keeping it here does not appear to be necessary. Therefore, this patch does not need to be considered further.
> 
> Thank you for your review.
> 
> Dear Gao Xiang,
> 
> Thank you for your review as well.
> 
> Best regards,
> Baolin Liu
>
> 

在 2026/1/6 11:30, Hongbo Li 写道:
> 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: