Hello Audit team, As I have not found a location anywhere else on the web, I am sending my question to this list. I have an Ubuntu 18.04 machine with auditd and it acts as a Docker Host machine. I have hardened the system via this package: https://github.com/konstruktoid/hardening which installs auditd with the configuration to be found here: https://github.com/konstruktoid/hardening/blob/master/misc/audit.rules. The problems I have are related to the directives -f and -b. The hardening package uses -b 8192 and -f 2. That results in a kernel panic very quickly because of audit backlog limit exceeded, and that causes a reboot of the system. Now I wonder what a good configuration would be. I started reading on the subject and read that -f 2 is probably the best for security reasons. However, I do not want to have a system that panics very quickly and reboots. Should I simply increase the backlog to much higher numbers? Or should I change -f to not cause a kernel panic? Or am I missing something and should I change some other configuration? Thanks for your help. Kind regards, Frederik Bosch -- Linux-audit mailing list Linux-audit(a)redhat.com https://www.redhat.com/mailman/listinfo/linux-audit

On Monday, August 20, 2018 5:56:04 AM EDT Frederik Bosch wrote: > As I have not found a location anywhere else on the web, I am sending my > question to this list. I have an Ubuntu 18.04 machine with auditd and it > acts as a Docker Host machine. I have hardened the system via this > package: https://github.com/konstruktoid/hardening which installs auditd > with the configuration to be found here: > https://github.com/konstruktoid/hardening/blob/master/misc/audit.rules. These rules could be improved upon by condensing: # File deletions # Capture all unauthorized file accesses # Capture all failures to access on critical elements # Permissions down to 2 rules in each, 4 for the second one. That, however, is not the actual problem. My guess is that it is capturing way more information than is necessary. > The problems I have are related to the directives -f and -b. The > hardening package uses -b 8192 and -f 2. That results in a kernel panic > very quickly because of audit backlog limit exceeded, and that causes a > reboot of the system. Now I wonder what a good configuration would be. I > started reading on the subject and read that -f 2 is probably the best > for security reasons. However, I do not want to have a system that > panics very quickly and reboots. I'd say that you need to run: aureport --start today --key --summary and see what rule is triggering all the events. Do you really want all deletes? Or just deletes in a specific directory? Do you really want to know that a user changed dir permissions on a file in their homedir? > Should I simply increase the backlog to much higher numbers? Or should I > change -f to not cause a kernel panic? Or am I missing something and > should I change some other configuration? Thanks for your help. For the moment change -f not to cause a kernel panic. I think the rules are probably too aggressive. -Steve

On Wednesday, August 22, 2018 7:40:56 AM EDT Frederik Bosch wrote: > Hi Steve, > > Thank you very much for your reply and your suggestion. I appreciate > that. The summary looks as follows. > > > Key Summary Report > =========================== > total key > =========================== > 63164 tmp > 16060 docker > 7206 delete > 6007 admin_user_home > 2760 auditlog > 1595 specialfiles > 675 perm_mod > 69 systemd > 54 systemd_tools > 36 init > 15 sshd > 12 cron > 5 login > 5 actions > 4 access > 3 privileged > 1 audit_rules_networkconfig_modification > > > Now I wonder why to watch /tmp and /var/tmp. This can be a staging ground for exploits. However, if they are mounted with the noexec option, they should be harmless. Also, the whole section titled: # Capture all failures to access on critical elements really is not necessary. Do you really need to know an open failed because of ENOENT? For example, every time a program is executed, ld.so tries to open 3 or 4 nonexisting files. This is not needed for security purposes and is normal system activity. The only time things matter is when you fail to open for permissions. About the docker section...why do you need to know all reads of those files? I'm not sure of the reason you'd want that information. -Steve > As it seems, these cause > most entries in the logs. Could you think of any reason why that would > be? I have also asked this question to the owner of the package. I will > reduce the number of delete calls to specific locations and disable > watches for /home as they seem to be inappropriate for my use case. > > Regards, > Frederik > > On 20-08-18 19:48, Steve Grubb wrote: >> On Monday, August 20, 2018 5:56:04 AM EDT Frederik Bosch wrote: >>> As I have not found a location anywhere else on the web, I am sending my >>> question to this list. I have an Ubuntu 18.04 machine with auditd and it >>> acts as a Docker Host machine. I have hardened the system via this >>> package: https://github.com/konstruktoid/hardening which installs auditd >>> with the configuration to be found here: >>> https://github.com/konstruktoid/hardening/blob/master/misc/audit.rules. >> These rules could be improved upon by condensing: >> >> # File deletions >> # Capture all unauthorized file accesses >> # Capture all failures to access on critical elements >> # Permissions >> >> down to 2 rules in each, 4 for the second one. That, however, is not the >> actual problem. My guess is that it is capturing way more information >> than is necessary. >> >>> The problems I have are related to the directives -f and -b. The >>> hardening package uses -b 8192 and -f 2. That results in a kernel panic >>> very quickly because of audit backlog limit exceeded, and that causes a >>> reboot of the system. Now I wonder what a good configuration would be. I >>> started reading on the subject and read that -f 2 is probably the best >>> for security reasons. However, I do not want to have a system that >>> panics very quickly and reboots. >> I'd say that you need to run: >> >> aureport --start today --key --summary >> >> and see what rule is triggering all the events. Do you really want all >> deletes? Or just deletes in a specific directory? Do you really want to >> know that a user changed dir permissions on a file in their homedir? >> >>> Should I simply increase the backlog to much higher numbers? Or should I >>> change -f to not cause a kernel panic? Or am I missing something and >>> should I change some other configuration? Thanks for your help. >> For the moment change -f not to cause a kernel panic. I think the rules >> are probably too aggressive. >> >> -Steve

On Wednesday, August 22, 2018 10:49:20 AM EDT Frederik Bosch wrote: > Hi Steve, > > That was really helpful, again. My aureport looks much healthier now! I > have one remaing question. When running auditctl -s I still have a lost > value of 51 after boot. > > enabled 2 > failure 1 > pid 779 > rate_limit 0 > backlog_limit 8192 > lost 51 > backlog 0 > backlog_wait_time 0 > loginuid_immutable 0 unlocked > > What could be the cause? By default, the audit subsystem reserves 64 slots for audit events. Systemd can easily overrun this before auditd starts. So, you need to boot with the following kernel boot options: audit=1 audit_backlog_limit=8192 Does you have this for boot options? > My aureport now looks like this. > > sudo aureport --start boot --key --summary > > Key Summary Report > =========================== > total key > =========================== > 289 auditlog > 120 specialfiles > 73 docker > 69 privileged > 29 access > 19 perm_mod > 17 delete > 12 actions > 11 audit_rules_networkconfig_modification > 10 cron > 10 modules > 10 login > 6 apparmor_tools > 6 audit_time_rules > 5 systemd_tools > 5 audit_rules_usergroup_modification > 5 pam > 4 power > 3 audittools > 3 group_modification > 3 user_modification > 3 init > 3 modprobe > 3 sshd > 2 apparmor > 2 systemd > 2 export > 2 auditconfig > 2 mail > 2 admin_user_home > 1 audispconfig > 1 MAC-policy > 1 passwd_modification > 1 logins > 1 libpath > 1 localtime > 1 audit_time_ruleszone > 1 sysctl > > If I understand things correctly with failure set to 1, I should find a > message in dmesg due to printk, but I have not found any that is > related. There may be a chance that these were lost before auditd rules were loaded. > My auditd.conf is as follows. > > local_events = yes > write_logs = yes > log_file = /var/log/audit/audit.log > log_group = adm > log_format = RAW > flush = INCREMENTAL_ASYNC > freq = 50 > max_log_file = 8 > num_logs = 5 Btw, these two settings only allow 40Mb of logs. Typically if you really need auditing you need more than this. > priority_boost = 4 > disp_qos = lossy > dispatcher = /sbin/audispd > name_format = NONE > ##name = mydomain > max_log_file_action = keep_logs > space_left = 75 > space_left_action = email > verify_email = yes > action_mail_acct = root > admin_space_left = 50 > admin_space_left_action = halt > disk_full_action = SUSPEND > disk_error_action = SUSPEND > use_libwrap = yes > ##tcp_listen_port = 60 > tcp_listen_queue = 5 > tcp_max_per_addr = 1 > ##tcp_client_ports = 1024-65535 > tcp_client_max_idle = 0 > enable_krb5 = no > krb5_principal = auditd > ##krb5_key_file = /etc/audit/audit.key > distribute_network = no > > Or is it something I should not be worried about? Maybe. Let's see what the boot options are. Also, what kernel version are you using? -Steve