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Date:   Mon, 31 May 2021 23:31:00 +0800
From:   Changbin Du <changbin.du@gmail.com>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Cong Wang' <xiyou.wangcong@gmail.com>,
        Changbin Du <changbin.du@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kici nski <kuba@kernel.org>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>
Subject: Re: [PATCH] net: fix oops in socket ioctl cmd SIOCGSKNS when NET_NS
 is disabled
Message-ID: <20210531153100.pfwlrkrqdisp6heu@mail.google.com>
References: <20210529060526.422987-1-changbin.du@gmail.com>
 <CAM_iQpWwApLVg39rUkyXxnhsiP0SZf=0ft6vsq=VxFtJ2SumAQ@mail.gmail.com>
 <55effe20acc54ea4a96ea86015d99a5b@AcuMS.aculab.com>
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On Mon, May 31, 2021 at 08:30:58AM +0000, David Laight wrote:
> From: Cong Wang
> > Sent: 29 May 2021 20:15
> > 
> > On Fri, May 28, 2021 at 11:08 PM Changbin Du <changbin.du@gmail.com> wrote:
> > > diff --git a/net/socket.c b/net/socket.c
> > > index 27e3e7d53f8e..644b46112d35 100644
> > > --- a/net/socket.c
> > > +++ b/net/socket.c
> > > @@ -1149,11 +1149,15 @@ static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
> > >                         mutex_unlock(&vlan_ioctl_mutex);
> > >                         break;
> > >                 case SIOCGSKNS:
> > > +#ifdef CONFIG_NET_NS
> > >                         err = -EPERM;
> > >                         if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
> > >                                 break;
> > >
> > >                         err = open_related_ns(&net->ns, get_net_ns);
> > > +#else
> > > +                       err = -ENOTSUPP;
> > > +#endif
> > 
> > I wonder if it is easier if we just reject ns->ops==NULL case
> > in open_related_ns(). For 1) we can save an ugly #ifdef here;
> > 2) drivers/net/tun.c has the same bugs.
> 
> If CONFIG_NET_NS is unset then why not make both ns_capable()
> and open_related_ns() unconditionally return -ENOTSUPP?
>
Here is the new fix that reject creating indoe for disabled ns.
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -62,6 +62,10 @@ static int __ns_get_path(struct path *path, struct ns_common *ns)
        struct inode *inode;
        unsigned long d;
 
+       /* In case the namespace is not actually enabled. */
+       if (!ns->ops)
+               return -EOPNOTSUPP;

> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)

-- 
Cheers,
Changbin Du