CentOS7 iproute hang inside OpenVZ7 CTs

Igor Vishnevsky (igor1601):
>Description of problem:
After iproute upgrade to 4.11.0-14.el7 (part of CentOS 7.5 upgrade) there was a problem with the hanging of iproute utilities - ss and ip.
Reboot of CT didn't help.
Downgrade to previous version (iproute-3.10.0-87.el7) fixes the problem.
The problem is inherent only inside OpenVZ 7 CT's with CentOS7 (tested only CentOS6 and CentOS7 guest OS). CT's with CentOS7 in OpenVZ6 or dedicated servers with CentOS 7 are not affected.
 
>How reproducible:
Uprade iproute package from base repo.

>Steps to Reproduce:
1. yum update
2. or yum update iproute
3. ip addr or ss -nltp

>Actual results:
ss or ip hangs, network can't stop/start/restart

>Expected results:
Normal work of iproute utilities

>Host OS:
Linux 3.10.0-693.21.1.vz7.46.3 #1 SMP Mon Apr 2 18:21:35 MSK 2018 x86_64 x86_64 x86_64 GNU/Linux

>Guest OS:
CentOS Linux release 7.5.1804 (Core)
Linux testct 3.10.0 #1 SMP Mon Apr 2 18:21:35 MSK 2018 x86_64 x86_64 x86_64 GNU/Linux
iproute2-ss170501

>Additional info (see https://openvz.org/Reporting_OpenVZ_problem):
strace result of ip addr:
CT-c19bbd01 ~# strace ip addr
execve("/sbin/ip", ["ip", "addr"], [/* 17 vars */]) = 0
brk(NULL) = 0xdca000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fdd273af000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=17948, ...}) = 0
mmap(NULL, 17948, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fdd273aa000
close(3) = 0
open("/lib64/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`\16\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=19776, ...}) = 0
mmap(NULL, 2109744, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fdd26f8b000
mprotect(0x7fdd26f8d000, 2097152, PROT_NONE) = 0
mmap(0x7fdd2718d000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fdd2718d000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P%\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2173512, ...}) = 0
mmap(NULL, 3981792, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fdd26bbe000
mprotect(0x7fdd26d81000, 2093056, PROT_NONE) = 0
mmap(0x7fdd26f80000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c2000) = 0x7fdd26f80000
mmap(0x7fdd26f86000, 16864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fdd26f86000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fdd273a9000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fdd273a7000
arch_prctl(ARCH_SET_FS, 0x7fdd273a7740) = 0
mprotect(0x7fdd26f80000, 16384, PROT_READ) = 0
mprotect(0x7fdd2718d000, 4096, PROT_READ) = 0
mprotect(0x669000, 4096, PROT_READ) = 0
mprotect(0x7fdd273b0000, 4096, PROT_READ) = 0
munmap(0x7fdd273aa000, 17948) = 0
socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE) = 3
setsockopt(3, SOL_SOCKET, SO_SNDBUF, [32768], 4) = 0
setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
setsockopt(3, SOL_NETLINK, 11, [1], 4) = 0
bind(3, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0
getsockname(3, {sa_family=AF_NETLINK, pid=2160, groups=00000000}, [12]) = 0
sendto(3, "(\0\0\0\22\0\1\3\231 \364Z\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 40, 0, NULL, 0) = 40
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{NULL, 0}], msg_controllen=0, msg_flags=MSG_TRUNC}, MSG_PEEK|MSG_TRUNC) = 40
brk(NULL) = 0xdca000
brk(0xdeb000) = 0xdeb000
brk(NULL) = 0xdeb000
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"(\0\0\0\22\0\1\3\231 \364Z\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 40}], msg_controllen=0, msg_flags=0}, 0) = 40
recvmsg(3,