On 2019/6/4 18:46, Miroslav Benes wrote:
> On Mon, 3 Jun 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 <yuehaib...@huawei.com>
>> ---
>> v3: reuse module_remove_modinfo_attrs
>> v2: free from '--i' instead of 'i--'
>> ---
>> kernel/module.c | 21 ++++++++++++++++-----
>> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> I'm afraid it is not completely correct.
>
>> diff --git a/kernel/module.c b/kernel/module.c
>> index 80c7c09..c6b8912 100644
>> --- a/kernel/module.c
>> +++ b/kernel/module.c
>> @@ -1697,6 +1697,8 @@ static int add_usage_links(struct module *mod)
>> return ret;
>> }
>>
>> +static void module_remove_modinfo_attrs(struct module *mod, int end);
>> +
>> static int module_add_modinfo_attrs(struct module *mod)
>> {
>> struct module_attribute *attr;
>> @@ -1711,24 +1713,33 @@ 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;
>
> sysfs_create_file() failed, so we need to clear all previously processed
> attrs and not the current one.
>
>> ++temp_attr;
>> }
>> }
>> +
>> + return 0;
>> +
>> +error_out:
>> + module_remove_modinfo_attrs(mod, --i);
>
> It says "call sysfs_remove_file() on all attrs ending with --i included
> (all correctly processed attrs).
>
>> return error;
>> }
>>
>> -static void module_remove_modinfo_attrs(struct module *mod)
>> +static void module_remove_modinfo_attrs(struct module *mod, int end)
>> {
>> struct module_attribute *attr;
>> int i;
>>
>> for (i = 0; (attr = &mod->modinfo_attrs[i]); i++) {
>> + if (end >= 0 && i > end)
>> + break;
>
> If end == 0, you break the loop without calling sysfs_remove_file(), which
> is a bug if you called module_remove_modinfo_attrs(mod, 0).
If end == 0 and i == 0, if statement is false, it won't break the loop.
At other places, I use end == -1, which means clean all and keeps the old
behavior
- module_remove_modinfo_attrs(mod);
+ module_remove_modinfo_attrs(mod, -1);
>
> Calling module_remove_modinfo_attrs(mod, i); in module_add_modinfo_attrs()
> under error_out label and changing the condition here to
>
> if (end >= 0 && i >= end)
> break;
>
> should work as expected.
>
> But let me ask another question and it might be more to Jessica. Why is
> there even a call to attr->free(mod); (if it exists) in
> module_remove_modinfo_attrs()? The same is in free_modinfo() (as opposed
> to setup_modinfo() where attr->setup(mod) is called. Is it because
> free_modinfo() is called only in load_module()'s error path, while
> module_remove_modinfo_attrs() is called even in free_module() path?
>
> kfree() checks for NULL pointer, so there is no bug, but it is certainly
> not nice and it calls for cleanup. But I may be missing something.
>
> Regards,
> Miroslav
>
> .
>
