On Wed, Aug 19, 2020 at 7:06 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > On Wed, Aug 19, 2020 at 3:54 PM syzbot > <syzbot+df400f2f24a1677cd7e0@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 18445bf4 Merge tag 'spi-fix-v5.9-rc1' of git://git.kernel... > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1710d97a900000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=bb68b9e8a8cc842f > > dashboard link: https://syzkaller.appspot.com/bug?extid=df400f2f24a1677cd7e0 > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15859986900000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1228fea1900000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+df400f2f24a1677cd7e0@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > unregister_netdevice: waiting for lo to become free. Usage count = 1 > > Based on the repro, it looks bpf/bpf link related: > > syz_emit_ethernet(0x86, &(0x7f0000000000)={@local, @empty=[0x2], > @void, {@ipv4={0x800, @udp={{0x5, 0x4, 0x0, 0x0, 0x78, 0x0, 0x0, 0x0, > 0x11, 0x0, @empty, @empty}, {0x0, 0x1b59, 0x64, 0x0, > @wg=@response={0x5, 0x0, 0x0, "020000010865390406030500000000010900", > "9384bbeb3018ad591b661fe808b21b77", > {"694c875dfb1be5d2a0057a62022a1564", > "a329d3a73b8268129e5fa4316a5d8c69"}}}}}}}, 0x0) > mkdirat(0xffffffffffffff9c, &(0x7f0000000000)='./file0\x00', 0x0) > mount(0x0, &(0x7f0000000080)='./file0\x00', > &(0x7f0000000040)='cgroup2\x00', 0x0, 0x0) > r0 = openat$cgroup_root(0xffffffffffffff9c, &(0x7f0000000000), 0x200002, 0x0) > r1 = bpf$PROG_LOAD(0x5, &(0x7f0000000080)={0x9, 0x4, > &(0x7f0000000000)=@framed={{}, [@alu={0x8000000201a7f19, 0x0, 0x6, > 0x2, 0x1}]}, &(0x7f0000000100)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, [], > 0x0, 0x0, 0xffffffffffffffff, 0x8, 0x0, 0x0, 0x10, 0x0}, 0x70) > bpf$BPF_LINK_CREATE(0x1c, &(0x7f0000000100)={r1, r0, 0x2}, 0x10) > The only place where BPF link-related code is bumping refcount for net_device is in bpf_xdp_link_attach(), but both success and failure code paths always do dev_put() in the end. bpf_link itself has a pointer on net_device, but it's protected by rtnl_lock() only, no refcnt associated with it. So I don't see how bpf_link can cause this. I also couldn't reproduce this locally, using the provided C reproducer. > > --- > > This report 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@xxxxxxxxxxxxxxxx. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > syzbot can test patches for this issue, for details see: > > https://goo.gl/tpsmEJ#testing-patches
