Re: general protection fault in __netlink_ns_capable

[Eric Biggers]

On Thu, Jan 04, 2018 at 10:14:38AM -0800, Andrei Vagin wrote:
> 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.

This crash is no longer occurring, thanks Andrei!  The Reported-by tag didn't
actually make it into the commit (f428fe4a04cc), so I'll tell syzbot instead:

#syz fix: rtnetlink: give a user socket to get_target_net()

- Eric