Re: Configuration files are not resilient to power failure

I've added a call to fsync in 5-7-patches and master.

On Mon, 15 Jan 2018 04:18:57 -0500 (EST) Josef wrote:
JR> net-snmp's configuration files are not resilient to power
JR> failure.
JR> 
JR> following a power failure event users created with
JR> net-snmp-create-v3-user are missing from /etc/snmp/snmpd.conf
JR> and that /var/lib/net-snmp/snmpd.conf is empty.
JR> 
JR> Steps to Reproduce:
JR> 
JR>   [root@rhel73 ~]# cat /etc/fstab
JR>   UUID=8c3e7419-f4b9-425a-b535-b6849a6e68bf / xfs defaults 0 0
JR>   [root@rhel73 ~]# grep
JR> testuser /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
JR> [root@rhel73 ~]# ls
JR> -l /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
JR> -rw-------. 1 root root 18891 Dec  4 22:32 /etc/snmp/snmpd.conf
JR> -rw-------. 1 root root  1073 Dec  5
JR> 00:04 /var/lib/net-snmp/snmpd.conf
JR> 
JR>   [root@rhel73 ~]# systemctl stop snmpd
JR>   [root@rhel73 ~]# /usr/bin/net-snmp-create-v3-user -A testpass
JR> testuser
JR> 
JR>   [root@rhel73 ~]# ls
JR> -l /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
JR> -rw-------. 1 root root 18877 Dec  5 00:09 /etc/snmp/snmpd.conf
JR> -rw-------. 1 root root  1112 Dec  5
JR> 00:09 /var/lib/net-snmp/snmpd.con [root@rhel73 ~]# grep
JR> testuser /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf /etc/snmp/snmpd.conf:rwuser
JR> testuser /var/lib/net-snmp/snmpd.conf:createUser testuser MD5
JR> "testpass" DES
JR> 
JR>   [root@rhel73 ~]# systemctl start snmpd
JR> 
JR> Force power off and reconnect.
JR> 
JR>   [root@rhel73 ~]#  grep
JR> testuser /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
JR> [root@rhel73 ~]#  ls
JR> -l /etc/snmp/snmpd.conf /var/lib/net-snmp/snmpd.conf
JR> -rw-------. 1 root root 18861 Dec  5 00:09 /etc/snmp/snmpd.conf
JR> -rw-------. 1 root root     0 Dec  5
JR> 00:09 /var/lib/net-snmp/snmpd.conf
JR> 
JR> Actual results:
JR> 
JR>   The added user has been lost from the configuration.
JR>   The entire /var/lib/net-snmp/snmpd.conf has been lost.
JR> 
JR> Expected results:
JR> 
JR>   /etc/snmp/snmpd.conf contains the newly added user.
JR>   /var/lib/net-snmp/snmpd.conf  is not destroyed.
JR> 
JR> Additional info:
JR> 
JR>   This was observed for XFS root filesystems, it may be that
JR> the default Ext's data=ordered mode behaves differently.
JR> Running this under strace snmpd is doing a rename/rewrite of
JR> the file. But it never calls fsync, so for the XFS case the
JR> dirty buffers are still in memory when the box is powered off,
JR> only the rename and create have hit the disk.

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