Re: BUG: using smp_processor_id() in preemptible [ADDR] code: syz-executor

[Dmitry Vyukov]

On Sun, Jun 30, 2019 at 7:19 AM Hillf Danton <hdanton@xxxxxxxx> wrote:
>
>
> Hello,
>
> On Sat, 29 Jun 2019 08:47:06 -0700 (PDT)
> > syzbot found the following crash on:
> >
> > HEAD commit:    ee7dd773 sis900: remove TxIDLE
> > git tree:       net-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=17ceb9a9a00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=7ac9edef4d37e5fb
> > dashboard link: https://syzkaller.appspot.com/bug?extid=1a68504d96cd17b33a05
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=119b2a13a00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13127bada00000
> >
> > The bug was bisected to:
>
> Hm... I doubt it is e9c1a793210f ("tipc: add dst_cache support for udp media")
> based on one of the lines dumped:
>
>         >   tipc_udp_xmit.isra.0+0xc4/0xb80 net/tipc/udp_media.c:164
>
>
> And getting the local bottom half disabled looks like a teaspoon of
> cough syrup.
> ---
>
> --- a/net/tipc/udp_media.c
> +++ b/net/tipc/udp_media.c
> @@ -224,6 +224,8 @@ static int tipc_udp_send_msg(struct net *net, struct sk_buff *skb,
>         struct udp_bearer *ub;
>         int err = 0;
>
> +       local_bh_disable();
> +
>         if (skb_headroom(skb) < UDP_MIN_HEADROOM) {
>                 err = pskb_expand_head(skb, UDP_MIN_HEADROOM, 0, GFP_ATOMIC);
>                 if (err)
> @@ -237,9 +239,12 @@ static int tipc_udp_send_msg(struct net *net, struct sk_buff *skb,
>                 goto out;
>         }
>
> -       if (addr->broadcast != TIPC_REPLICAST_SUPPORT)
> -               return tipc_udp_xmit(net, skb, ub, src, dst,
> +       if (addr->broadcast != TIPC_REPLICAST_SUPPORT) {
> +               err = tipc_udp_xmit(net, skb, ub, src, dst,
>                                      &ub->rcast.dst_cache);
> +               local_bh_enable();
> +               return err;
> +       }
>
>         /* Replicast, send an skb to each configured IP address */
>         list_for_each_entry_rcu(rcast, &ub->rcast.list, list) {
> @@ -259,6 +264,7 @@ static int tipc_udp_send_msg(struct net *net, struct sk_buff *skb,
>         err = 0;
>  out:
>         kfree_skb(skb);
> +       local_bh_enable();
>         return err;
>  }
>
> --
>
> > commit 52dfae5c85a4c1078e9f1d5e8947d4a25f73dd81
> > Author: Jon Maloy <jon.maloy@xxxxxxxxxxxx>
> > Date:   Thu Mar 22 19:42:52 2018 +0000
> >
> >      tipc: obtain node identity from interface by default

What is the fate of this fix?
There is also another fix for this pending for half a year as far as I can tell.

This is one of the top crashes and it prevents most other kernel
testing from happening.  All kernels just crash on this right away.


> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=160ad903a00000
> > final crash:    https://syzkaller.appspot.com/x/report.txt?x=150ad903a00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=110ad903a00000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+1a68504d96cd17b33a05@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: 52dfae5c85a4 ("tipc: obtain node identity from interface by default")
> >
> > Started in network mode
> > Own node identity 7f000001, cluster identity 4711
> > New replicast peer: 172.20.20.22
> > check_preemption_disabled: 3 callbacks suppressed
> > BUG: using smp_processor_id() in preemptible [00000000] code:
> > syz-executor834/8612
> > caller is dst_cache_get+0x3d/0xb0 net/core/dst_cache.c:68
> > CPU: 0 PID: 8612 Comm: syz-executor834 Not tainted 5.2.0-rc6+ #48
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:77 [inline]
> >   dump_stack+0x172/0x1f0 lib/dump_stack.c:113
> >   check_preemption_disabled lib/smp_processor_id.c:47 [inline]
> >   debug_smp_processor_id+0x251/0x280 lib/smp_processor_id.c:57
> >   dst_cache_get+0x3d/0xb0 net/core/dst_cache.c:68
> >   tipc_udp_xmit.isra.0+0xc4/0xb80 net/tipc/udp_media.c:164
> >   tipc_udp_send_msg+0x29a/0x4b0 net/tipc/udp_media.c:254
> >   tipc_bearer_xmit_skb+0x16c/0x360 net/tipc/bearer.c:503
> >   tipc_enable_bearer+0xabe/0xd20 net/tipc/bearer.c:328
> >   __tipc_nl_bearer_enable+0x2de/0x3a0 net/tipc/bearer.c:899
> >   tipc_nl_bearer_enable+0x23/0x40 net/tipc/bearer.c:907
> >   genl_family_rcv_msg+0x74b/0xf90 net/netlink/genetlink.c:629
> >   genl_rcv_msg+0xca/0x16c net/netlink/genetlink.c:654
> >   netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
> >   genl_rcv+0x29/0x40 net/netlink/genetlink.c:665
> >   netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
> >   netlink_unicast+0x531/0x710 net/netlink/af_netlink.c:1328
> >   netlink_sendmsg+0x8ae/0xd70 net/netlink/af_netlink.c:1917
> >   sock_sendmsg_nosec net/socket.c:646 [inline]
> >   sock_sendmsg+0xd7/0x130 net/socket.c:665
> >   ___sys_sendmsg+0x803/0x920 net/socket.c:2286
> >   __sys_sendmsg+0x105/0x1d0 net/socket.c:2324
> >   __do_sys_sendmsg net/socket.c:2333 [inline]
> >   __se_sys_sendmsg net/socket.c:2331 [inline]
> >   __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2331
> >   do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
> >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x444679
> > Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7
> > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> > ff 0f 83 1b d8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007fff0201a8b8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> > RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000444679
> > RDX: 0000000000000000 RSI: 0000000020000580 RDI: 0000000000000003
> > RBP: 00000000006cf018 R08: 0000000000000001 R09: 00000000004002e0
> > R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000402320
> > R13: 00000000004023b0 R14: 0000000000000000 R15: 0000000000
> >
> >
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >
>
>
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