On Mon, Oct 24, 2022 at 10:39:44PM +0800, Yang Yingliang wrote:
>
> On 2022/10/24 21:52, Greg KH wrote:
> > On Mon, Oct 24, 2022 at 08:19:10PM +0800, Yang Yingliang wrote:
> > > Inject fault while loading module, kset_register() may fail.
> > > If it fails, the name allocated by kobject_set_name() which
> > > is called before kset_register() is leaked, because refcount
> > > of kobject is hold in kset_init().
> > >
> > > As a kset may be embedded in a larger structure which needs
> > > be freed in release() function or error path in callers, we
> > > can not call kset_put() in kset_register(), or it will cause
> > > double free, so just call kfree_const() to free the name and
> > > set it to NULL.
> > >
> > > With this fix, the callers don't need to care about the name
> > > freeing and call an extra kset_put() if kset_register() fails.
> > >
> > > Suggested-by: Luben Tuikov <[email protected]>
> > > Signed-off-by: Yang Yingliang <[email protected]>
> > > ---
> > > v1 -> v2:
> > > Free name inside of kset_register() instead of calling kset_put()
> > > in drivers.
> > > ---
> > > lib/kobject.c | 8 +++++++-
> > > 1 file changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/lib/kobject.c b/lib/kobject.c
> > > index a0b2dbfcfa23..3409a89c81e5 100644
> > > --- a/lib/kobject.c
> > > +++ b/lib/kobject.c
> > > @@ -834,6 +834,9 @@ EXPORT_SYMBOL_GPL(kobj_sysfs_ops);
> > > /**
> > > * kset_register() - Initialize and add a kset.
> > > * @k: kset.
> > > + *
> > > + * NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
> > > + * which is called before kset_register() in caller need be freed.
> > This comment doesn't make any sense anymore. No caller needs to worry
> > about this, right?
> With this fix, the name is freed inside of kset_register(), it can not be
> accessed,
Agreed.
> if it allocated dynamically, but callers don't know this if no comment here,
> they may use it in error path (something like to print error message with
> it),
> so how about comment like this to tell callers not to use the name:
>
> NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
> is freed, it can not be used any more.
Sure, that's a better way to word it.
> > > */
> > > int kset_register(struct kset *k)
> > > {
> > > @@ -844,8 +847,11 @@ int kset_register(struct kset *k)
> > > kset_init(k);
> > > err = kobject_add_internal(&k->kobj);
> > > - if (err)
> > > + if (err) {
> > > + kfree_const(k->kobj.name);
> > > + k->kobj.name = NULL;
> > Why are you setting the name here to NULL?
> I set it to NULL to avoid accessing bad pointer in callers,
> if callers use it in error path, current callers won't use this
> name pointer in error path, so we can remove this assignment?
Ah, I didn't think about using it on error paths. Ideally that would
never happen, but that's good to set just to make it obvious. How about
adding a small comment here saying why you are setting it so we all
remember it in 5 years when we look at the code again.
thanks,
greg k-h
On 2022/10/24 22:53, Greg KH wrote:
> On Mon, Oct 24, 2022 at 10:39:44PM +0800, Yang Yingliang wrote:
>> On 2022/10/24 21:52, Greg KH wrote:
>>> On Mon, Oct 24, 2022 at 08:19:10PM +0800, Yang Yingliang wrote:
>>>> Inject fault while loading module, kset_register() may fail.
>>>> If it fails, the name allocated by kobject_set_name() which
>>>> is called before kset_register() is leaked, because refcount
>>>> of kobject is hold in kset_init().
>>>>
>>>> As a kset may be embedded in a larger structure which needs
>>>> be freed in release() function or error path in callers, we
>>>> can not call kset_put() in kset_register(), or it will cause
>>>> double free, so just call kfree_const() to free the name and
>>>> set it to NULL.
>>>>
>>>> With this fix, the callers don't need to care about the name
>>>> freeing and call an extra kset_put() if kset_register() fails.
>>>>
>>>> Suggested-by: Luben Tuikov <[email protected]>
>>>> Signed-off-by: Yang Yingliang <[email protected]>
>>>> ---
>>>> v1 -> v2:
>>>> Free name inside of kset_register() instead of calling kset_put()
>>>> in drivers.
>>>> ---
>>>> lib/kobject.c | 8 +++++++-
>>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/kobject.c b/lib/kobject.c
>>>> index a0b2dbfcfa23..3409a89c81e5 100644
>>>> --- a/lib/kobject.c
>>>> +++ b/lib/kobject.c
>>>> @@ -834,6 +834,9 @@ EXPORT_SYMBOL_GPL(kobj_sysfs_ops);
>>>> /**
>>>> * kset_register() - Initialize and add a kset.
>>>> * @k: kset.
>>>> + *
>>>> + * NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
>>>> + * which is called before kset_register() in caller need be freed.
>>> This comment doesn't make any sense anymore. No caller needs to worry
>>> about this, right?
>> With this fix, the name is freed inside of kset_register(), it can not be
>> accessed,
> Agreed.
>
>> if it allocated dynamically, but callers don't know this if no comment here,
>> they may use it in error path (something like to print error message with
>> it),
>> so how about comment like this to tell callers not to use the name:
>>
>> NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
>> is freed, it can not be used any more.
> Sure, that's a better way to word it.
>
>>>> */
>>>> int kset_register(struct kset *k)
>>>> {
>>>> @@ -844,8 +847,11 @@ int kset_register(struct kset *k)
>>>> kset_init(k);
>>>> err = kobject_add_internal(&k->kobj);
>>>> - if (err)
>>>> + if (err) {
>>>> + kfree_const(k->kobj.name);
>>>> + k->kobj.name = NULL;
>>> Why are you setting the name here to NULL?
>> I set it to NULL to avoid accessing bad pointer in callers,
>> if callers use it in error path, current callers won't use this
>> name pointer in error path, so we can remove this assignment?
> Ah, I didn't think about using it on error paths. Ideally that would
> never happen, but that's good to set just to make it obvious. How about
> adding a small comment here saying why you are setting it so we all
> remember it in 5 years when we look at the code again.
OK, I can add it in v3.
Thanks,
Yang
>
> thanks,
>
> greg k-h
> .