On Tue, 22 Apr 2025 13:44:39 +0300 Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> On Tue, Apr 22, 2025 at 01:38:05PM +0300, Dan Carpenter wrote:
> > On Mon, Apr 21, 2025 at 02:24:24PM +0800, Su Hui wrote:
> > > It's safer to using kmalloc_array() and size_add() because it can
> > > prevent possible overflow problem.
> > >
> > > Signed-off-by: Su Hui <suhui@xxxxxxxxxxxx>
[...]
> > > --- a/mm/damon/sysfs-schemes.c
> > > +++ b/mm/damon/sysfs-schemes.c
> > > @@ -465,7 +465,8 @@ static ssize_t memcg_path_store(struct kobject *kobj,
> > > {
> > > struct damon_sysfs_scheme_filter *filter = container_of(kobj,
> > > struct damon_sysfs_scheme_filter, kobj);
> > > - char *path = kmalloc(sizeof(*path) * (count + 1), GFP_KERNEL);
> > > + char *path = kmalloc_array(size_add(count, 1), sizeof(*path),
> > > + GFP_KERNEL);
> >
> > Count is clamped in rw_verify_area().
> >
> > Smatch does a kind of ugly hack to handle rw_verify_area() which is that
> > it says neither the count nor the pos can be more than 1G. And obviously
> > files which are larger than 2GB exist but pretending they don't silences
> > all these integer overflow warnings.
> >
>
> Actually rw_verify_area() ensures that "pos + count" can't overflow. But
> here we are multiplying. Fortunately, we are multiplying by 1 so that's
> safe and also count can't be larger than PAGE_SIZE here which is safe as
> well.
Thank you for adding these details, Dan. I understand the size_add() change
can make warnings slience, though it is not really fixing a real bug. So I
believe there is no action item to make a change to this patch. Maybe making
the commit message more clarified can be helpful, though?
Please let me know if I'm misunderstanding your point and/or you want some
changes.
Thanks,
SJ
>
> regards,
> dan carpenter
