Re: general protection fault in __netlink_ns_capable

[Dmitry Vyukov]

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:

> > 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.