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    SubjectRe: general protection fault in __netlink_ns_capable
    On Wed, Jan 3, 2018 at 8:37 AM, Andrei Vagin <avagin@virtuozzo.com> 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@syzkaller.appspotmail.com
    >> > 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@syzkaller.appspotmail.com
    > > It will help syzbot understand when the bug is fixed.

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