[pkg-netfilter-team] Bug#919325: iptables -nvL consumes 100% of CPU and hogs memory with kernel 5.0-rc2

[Martin Steigerwald]

Package: iptables
Version: 1.8.2-3
Severity: important

Dear Maintainer,

for now I am rating this important. If it happens for many users it may
have a higher severity. It may however also be a kernel issue, as it
happened after upgrading to self-compiled 5.0-rc2.

I upgraded to self-compiled 5.0-rc2 today and found the machine to be slow
after startup. I saw iptables consuming 100% CPU, it only responded to
SIGKILL. It got restarted several times, probably by some systemd service.

Then I started 'iptables -nvL' manually. And I got this:

% strace -p 5748
[… tons more, in what appeared an endless loop …]
recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
recvmsg(3, ^C{msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
strace: Process 5748 detached

and this (output from atop):

  PID     TID   MINFLT   MAJFLT    VSTEXT   VSLIBS    VDATA    VSTACK    VSIZE    RSIZE    PSIZE     VGROW    RGROW   SWAPSZ    RUID       EUID        MEM   CMD        1/16
11575       -    61552        0      152K    2324K     5.0G      132K     5.1G     5.1G       0K    240.4M   240.5M       0K    root       root        33%   iptables

I had it growing till 10 GiB before I stopped it by SIGKILL to prevent
excessive swapping.

I will attach kernel configuration.

That is all I am willing to spend time on for now before going to sleep.
I will however reboot with older 4.20 kernel to see whether it is kernel
related.

Thanks,
Martin

-- System Information:
Debian Release: buster/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable'), (200, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.0.0-rc2-tp520 (SMP w/4 CPU cores; PREEMPT)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE=de (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages iptables depends on:
ii  libc6                    2.28-5
ii  libip4tc0                1.8.2-3
ii  libip6tc0                1.8.2-3
ii  libiptc0                 1.8.2-3
ii  libmnl0                  1.0.4-2
ii  libnetfilter-conntrack3  1.0.7-1
ii  libnfnetlink0            1.0.1-3+b1
ii  libnftnl11               1.1.2-2
ii  libxtables12             1.8.2-3

Versions of packages iptables recommends:
ii  nftables  0.9.0-2

Versions of packages iptables suggests:
ii  kmod  25-2

-- no debconf information