Re: BUG: kernel NULL pointer dereference in __cgroup_bpf_run_filter_skb

[Daniel Borkmann <daniel@iogearbox.net>]

On 6/30/20 4:28 PM, Rudi Ratloser wrote:
> We have experienced a kernel BPF null pointer dereference issue on all
> our machines since mid of June. It might be related to an upgrade of
> libvirt/kvm/qemu at that point of time. But we’re not sure.
> 
> None of the servers can be used with this bug, as they crash latest
> one hour after reboot. The time period until kernel panic can be
> easily reduced down to 2 minutes, when starting one or more
> applications of the following list:
> - LXD daemon (4.2.1)
> - libvirtd daemon (6.4.0) with qemu/kvm guests
> - NFS server 2.5.1
> - Mozilla Firefox
> - Mozilla Thunderbird
> 
> If none of the applications run, the systems seem to be stable.
> 
> Intermediate solution:
> Downgrade Linux kernel to 4.9.226 LTS or 4.4.226  LTS on all the machines
> 
> Why this solution works is not clear, yet. One of the major
> differences we saw is, that both kernel packages have been configured
> with user namespaces disabled.
> 
> We experienced the kernel freeze on following Arch Linux kernels:
> - 5.7.0 (5.7.0-3-MANJARO x64)
> - 5.6.16 (5.6.16-1-MANJARO x64)
> - 5.4.44 (5.4.44-1-MANJARO x64)
> - 4.19.126 (4.19.126-1-MANJARO x64)
> - 4.14.183 (4.14.183-1-MANJARO x64)
> Kernel configs can be taken from https://gitlab.manjaro.org/packages/core.
> 
> Subsequent e-mails will contain the relevant extracts from journal or
> netconsole logs.
> 
> Help and support on this issue is welcome.

Fix is under discussion here:

   https://lore.kernel.org/netdev/20200616180352.18602-1-xiyou.wangcong@gmail.com/

Thanks,
Daniel