Re: general protection fault in __netlink_ns_capable

[Andrei Vagin]

On Tue, Jan 02, 2018 at 04:35:11PM -0800, Andrei Vagin wrote:
> On Tue, Jan 02, 2018 at 10:58:01AM -0800, syzbot 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()