linux-kernel - Re: [PATCH net v2 2/3] net: core: add netdev_class_has_file

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Date:   Sun, 5 Apr 2020 02:18:22 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, rafael@...nel.org,
        j.vosburgh@...il.com, vfalico@...il.com,
        Andy Gospodarek <andy@...yhouse.net>,
        Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, mitch.a.williams@...el.com
Subject: Re: [PATCH net v2 2/3] net: core: add netdev_class_has_file_ns()
 helper function

On Sun, 5 Apr 2020 at 00:51, Greg KH <gregkh@...uxfoundation.org> wrote:
>

Hi Greg,
Thank you for your review!

> On Sat, Apr 04, 2020 at 02:19:09PM +0000, Taehee Yoo wrote:
> > This helper function is to check whether the class file "/sys/class/net/*"
> > is existing or not.
> > In the next patch, this helper function will be used.
> >
> > Reported-by: syzbot+830c6dbfc71edc4f0b8f@...kaller.appspotmail.com
> > Fixes: b76cdba9cdb2 ("[PATCH] bonding: add sysfs functionality to bonding (large)")
> > Signed-off-by: Taehee Yoo <ap420073@...il.com>
> > ---
> >
> > v1 -> v2:
> >  - use class_has_file_ns(), which is introduced by the first patch.
> >
> >  include/linux/netdevice.h | 2 +-
> >  net/core/net-sysfs.c      | 6 ++++++
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 130a668049ab..a04c487c0975 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -4555,7 +4555,7 @@ int netdev_class_create_file_ns(const struct class_attribute *class_attr,
> >                               const void *ns);
> >  void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
> >                                const void *ns);
> > -
> > +bool netdev_class_has_file_ns(const char *name, const void *ns);
> >  static inline int netdev_class_create_file(const struct class_attribute *class_attr)
> >  {
> >       return netdev_class_create_file_ns(class_attr, NULL);
> > diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> > index cf0215734ceb..8a20d658eff0 100644
> > --- a/net/core/net-sysfs.c
> > +++ b/net/core/net-sysfs.c
> > @@ -1914,6 +1914,12 @@ void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
> >  }
> >  EXPORT_SYMBOL(netdev_class_remove_file_ns);
> >
> > +bool netdev_class_has_file_ns(const char *name, const void *ns)
> > +{
> > +     return class_has_file_ns(&net_class, name, ns);
> > +}
> > +EXPORT_SYMBOL(netdev_class_has_file_ns);
>
> Again, this feels broken, it can not solve a race condition.
>

This function is considered to be used under rtnl mutex and
I assume that no one could use "/sys/class/net/*" outside of rtnl mutex.
So, I think it returns the correct information under rtnl mutex.

Thanks a lot!
Taehee Yoo