Re: Dnsmasq log setattr denial

[Lukas Vrabec]

Hi Jeff,

On 5/31/19 10:39 PM, Jeff Boyce wrote:
>  Greetings -
>  
>  I recently had some brief intermittent network connection issues that I
>  finally tracked down to occurring in time with dns lease renewal by
>  dnsmasq.  Looking into the logs I found that the issue began after I
>  rebooted my dns server recently.  No configuration changes had been
>  made, we shut servers down for a planned power outage for our building.
>  
>  I have read the full sealert message, but with my limited experience I
>  am looking for some confirmation before making any changes.  The raw
>  audit message is listed below.  It appears there may be a context issue
>  on the log file (I know there is a typo in my log file name).
>  
>  Raw Audit Messages
>  type=AVC msg=audit(1559298063.86:81599): avc:  denied  { setattr } for 
>  pid=15072 comm="dnsmasq" name="dsnmasq.log" dev=vda2 ino=1068
>  scontext=system_u:system_r:dnsmasq_t:s0
>  tcontext=system_u:object_r:var_log_t:s0 tclass=file
>  
>  type=SYSCALL msg=audit(1559298063.86:81599): arch=x86_64 syscall=fchown
>  success=no exit=EACCES a0=c a1=63 a2=ffffffff a3=418 items=0 ppid=1
>  pid=15072 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0
>  tty=(none) ses=13562 comm=dnsmasq exe=/usr/sbin/dnsmasq
>  subj=system_u:system_r:dnsmasq_t:s0 key=(null)
>  
>  Running audit2why gives the following, which references a missing type
>  enforcement allow rule.
>  
>  type=AVC msg=audit(1558865403.590:67806): avc:  denied  { setattr } for 
>  pid=1429 comm="dnsmasq" name="dsnmasq.log" dev=vda2 ino=827
>  scontext=system_u:system_r:dnsmasq_t:s0
>  tcontext=system_u:object_r:var_log_t:s0 tclass=file
>          Was caused by:
>                  Missing type enforcement (TE) allow rule.
>                  You can use audit2allow to generate a loadable module to
>  allow this access.
>  
>  However, when I run matchpathcon, I get the following results, which
>  seems to indicate that everything should be ok.
>  
>  [root@taxa ~]# matchpathcon -V /var/log/*
>  /var/log/dsnmasq.log verified.
>  /var/log/dsnmasq.log-20190525 verified.
>  /var/log/dsnmasq.log-20190526 verified.
>  /var/log/dsnmasq.log-20190527 verified.
>  /var/log/dsnmasq.log-20190528 verified.
>  /var/log/dsnmasq.log-20190529 verified.
>  /var/log/dsnmasq.log-20190530 verified.
>  /var/log/dsnmasq.log-20190531 verified.
>  
>  So it is not clear to me what is the proper way to resolve this denial,
>  and am looking for a little more education and advice so that I don't
>  issue the wrong selinux command.  I am running dnsmasq 2.48-18.el6_9 on
>  a CentOS 6 system.  Thanks.
>  
I think there is a typo in configuration file name /s/dsnmasq/dnsmasq.
This is your issue. You can rename the file, fix the configuration and
then run restorecon:

# restorecon -v /var/log/dnsmasq.log

or if you're using this for purpose (for whatever reason) you can assign
dnsmasq_var_log_t label to /var/log/dsnmasq.log:

# semanage fcontext -a -t dnsmasq_var_log_t "/var/log/dsnmasq\.log.*"
# restorecon -Rv /var/log/dsnmasq.log
Thanks,
Lukas.


>  Jeff
>   

-- 
Lukas Vrabec
Senior Software Engineer, Security Technologies
Red Hat, Inc.