Re: krealloc in kernel/params.c

[Rusty Russell <rusty@rustcorp.com.au>]

Rasmus Villemoes <linux@rasmusvillemoes.dk> writes:
> On Wed, Oct 15 2014, Rusty Russell <rusty@rustcorp.com.au> wrote:
>
>> Rasmus Villemoes <linux@rasmusvillemoes.dk> writes:
>> The kzalloc-then-always-krealloc pattern is perhaps overly simplistic,
>> but this code has clearly confused people.  It worked on me...
>>
>
> I think kzalloc immediately followed by kreallocing the returned value
> is rather ugly. Other than that:

Indeed, but it's an obvious pattern.  "If not initialized, initialize".

>> -		num = mk->mp->num;
>> -		attrs = mk->mp->grp.attrs;
>> +		/* First allocation. */
>> +		mk->mp = kzalloc(sizeof(*mk->mp), GFP_KERNEL);
>> +		if (!mk->mp)
>> +			return -ENOMEM;
>
> free_module_param_attrs does not check mk->mp for being NULL before
> kfree'ing mk->mp->grp.attrs, so this will oops.

Nice catch, folded this in:

diff --git a/kernel/params.c b/kernel/params.c
index 3ebe6c64aa67..ee92e67f2cee 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -650,7 +650,8 @@ static __modinit int add_sysfs_param(struct module_kobject *mk,
 #ifdef CONFIG_MODULES
 static void free_module_param_attrs(struct module_kobject *mk)
 {
-	kfree(mk->mp->grp.attrs);
+	if (mk->mp)
+		kfree(mk->mp->grp.attrs);
 	kfree(mk->mp);
 	mk->mp = NULL;
 }

Thanks!
Rusty.