Re: general protection fault in __netlink_ns_capable

[Andrei Vagin]

On Thu, Jan 04, 2018 at 01:01:17PM +0100, Dmitry Vyukov wrote:
> On Wed, Jan 3, 2018 at 8:37 AM, Andrei Vagin <avagin@xxxxxxxxxxxxx> wrote:
> >> > Hello,
> >> >
> >> > syzkaller hit the following crash on
> >> > 75aa5540627fdb3d8f86229776ea87f995275351
> >> > git://git.cmpxchg.org/linux-mmots.git/master
> >> > compiler: gcc (GCC) 7.1.1 20170620
> >> > .config is attached
> >> > Raw console output is attached.
> >> > C reproducer is attached
> >> > syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> >> > for information about syzkaller reproducers
> >> >
> >> >
> >> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >> > Reported-by: syzbot+e432865c29eb4c48c142@xxxxxxxxxxxxxxxxxxxxxxxxx
> >> > It will help syzbot understand when the bug is fixed. See footer for
> >> > details.
> >> > If you forward the report, please keep this part and the footer.
> >> >
> >> > netlink: 3 bytes leftover after parsing attributes in process
> >> > `syzkaller140561'.
> >> > netlink: 3 bytes leftover after parsing attributes in process
> >> > `syzkaller140561'.
> >> > netlink: 3 bytes leftover after parsing attributes in process
> >> > `syzkaller140561'.
> >> > kasan: CONFIG_KASAN_INLINE enabled
> >> > kasan: GPF could be caused by NULL-ptr deref or user memory access
> >> > general protection fault: 0000 [#1] SMP KASAN
> >> > Dumping ftrace buffer:
> >> >    (ftrace buffer empty)
> >> > Modules linked in:
> >> > CPU: 1 PID: 3149 Comm: syzkaller140561 Not tainted 4.15.0-rc4-mm1+ #47
> >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> >> > Google 01/01/2011
> >> > RIP: 0010:__netlink_ns_capable+0x8b/0x120 net/netlink/af_netlink.c:868
> >>
> >> NETLINK_CB(skb).sk is NULL here. It looks like we have to use
> >> sk_ns_capable instead of netlink_ns_capable:
> >>
> >> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> >> index c688dc564b11..408c75de52ea 100644
> >> --- a/net/core/rtnetlink.c
> >> +++ b/net/core/rtnetlink.c
> >> @@ -1762,7 +1762,7 @@ static struct net *get_target_net(struct sk_buff
> >> *skb, int netnsid)
> >>         /* For now, the caller is required to have CAP_NET_ADMIN in
> >>          * the user namespace owning the target net ns.
> >>          */
> >> -       if (!netlink_ns_capable(skb, net->user_ns, CAP_NET_ADMIN)) {
> >> +       if (!sk_ns_capable(skb->sk, net->user_ns, CAP_NET_ADMIN)) {
> >>                 put_net(net);
> >>                 return ERR_PTR(-EACCES);
> >>         }
> >>
> >
> > get_target_net() is used twice in the code. In rtnl_getlink(), we need
> > to use netlink_ns_capable(skb, ...), but in rtnl_dump_ifinfo, we need to
> > use sk_ns_capable(skb->sk, ...).
> >
> > Pls, take a look at this patch:
> > https://patchwork.ozlabs.org/patch/854896/
> > Subject: rtnetlink: give a user socket to get_target_net()
> 
> 
> Please include this tag into the commit:
> 

I sent v2 with this tag. Sorry for inconvenience.
https://patchwork.ozlabs.org/patch/855147/

> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+e432865c29eb4c48c142@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > It will help syzbot understand when the bug is fixed.