linux-kernel - Re: [PATCH v2] kernel/module: Fix mem leak in module_add_modinfo

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Date:   Mon, 3 Jun 2019 22:45:08 +0800
From:   Yuehaibing <yuehaibing@...wei.com>
To:     Miroslav Benes <mbenes@...e.cz>
CC:     <jeyu@...nel.org>, <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, <paulmck@...ux.ibm.com>
Subject: Re: [PATCH v2] kernel/module: Fix mem leak in
 module_add_modinfo_attrs

On 2019/6/3 20:11, Miroslav Benes wrote:
> On Thu, 30 May 2019, YueHaibing wrote:
> 
>> In module_add_modinfo_attrs if sysfs_create_file
>> fails, we forget to free allocated modinfo_attrs
>> and roll back the sysfs files.
>>
>> Fixes: 03e88ae1b13d ("[PATCH] fix module sysfs files reference counting")
>> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
>> ---
>> v2: free from '--i' instead of 'i--'  
>> ---
>>  kernel/module.c | 16 +++++++++++++++-
>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/module.c b/kernel/module.c
>> index 6e6712b..78e21a7 100644
>> --- a/kernel/module.c
>> +++ b/kernel/module.c
>> @@ -1723,15 +1723,29 @@ static int module_add_modinfo_attrs(struct module *mod)
>>  		return -ENOMEM;
>>  
>>  	temp_attr = mod->modinfo_attrs;
>> -	for (i = 0; (attr = modinfo_attrs[i]) && !error; i++) {
>> +	for (i = 0; (attr = modinfo_attrs[i]); i++) {
>>  		if (!attr->test || attr->test(mod)) {
>>  			memcpy(temp_attr, attr, sizeof(*temp_attr));
>>  			sysfs_attr_init(&temp_attr->attr);
>>  			error = sysfs_create_file(&mod->mkobj.kobj,
>>  					&temp_attr->attr);
>> +			if (error)
>> +				goto error_out;
>>  			++temp_attr;
>>  		}
>>  	}
>> +
>> +	return 0;
>> +
>> +error_out:
>> +	for (; (attr = &mod->modinfo_attrs[i]) && i >= 0; --i) {
>> +		if (!attr->attr.name)
>> +			break;
>> +		sysfs_remove_file(&mod->mkobj.kobj, &attr->attr);
>> +		if (attr->free)
>> +			attr->free(mod);
>> +	}
>> +	kfree(mod->modinfo_attrs);
>>  	return error;
>>  }
> 
> Hi,
> 
> would not be better to reuse the existing code in 
> module_remove_modinfo_attrs() instead of duplication? You could add a new 
> parameter "limit" or something and call the function here. I suppose the 
> order does not matter and if it does you could rename it "start" and go 
> backwards like in your patch.

This make sense, try do it in v3, thanks!

> 
> Btw, looking more into it, it would also be possible to let 
> mod_sysfs_setup() go to out_unreg_modinfo_attrs in case of an error from 
> module_add_modinfo_attrs() (and then clean the error handling in 
> mod_sysfs_setup() a bit). module_remove_modinfo_attrs() almost does the 
> right thing, because it checks attr->attr.name. The only problem is the
> last failing attribute, because it would have attr.name set, but its 
> sysfs_create_file() failed. So calling sysfs_remove_file() and the rest 
> would not be correct in that case.
> 
> Miroslav
> 
> .
>