Re: reactive audit proposal

On May 12, 2020, at 7:36 PM, Steve Grubb <sgrubb(a)redhat.com&gt; wrote: On Tuesday, May 12, 2020 8:31:45 PM EDT Joe Nall wrote: >> On May 12, 2020, at 7:22 PM, Steve Grubb <sgrubb(a)redhat.com&gt; wrote: >> >> Hello, >> >> I wanted to run this by the crowd to see what people's reaction might be. >> >> The audit system sometimes needs to have rules applied when something >> happens. For example, if someone plugs in a USB flash drive, the system >> creates the device in /dev and then automatically mounts it under some >> circumstances. >> >> I would propose 2 new additions to the audit rule syntax: on-mount and >> on-login.These rules would be in a separate file from the main audit >> rules. When a file system is mounted, /proc/mounts changes and the mount >> table can be scanned to see if something new is there. In this way we >> can reliably detect newly mounted filesystems. We can then match against >> a specifier to see if this is a file system in which we want to apply >> new rules. If so, we send the new rules to the kernel. When the device >> is unmounted, the kernel drops all watches on that file system. So, we >> only need to worry about when a device is mounted. >> >> This works good for anything that gets mounted. But it is also possible >> for a USB flash drive to be accessed as a block device, such as the dd >> utility. If we had to detect device discovery, there is a netlink group, >> NETLINK_KOBJECT_UEVENT which we could monitor for events. The only thing >> is that we could only detect open/read/write/close/ioctl/lseek. And we >> probably do not want to monitor anything except block devices. >> >> It may also be possible to poll /sys/block to watch for changes. This >> might be easier as the names are more friendly. This would take some >> research to see if its even possible. >> >> The rule syntax could look something like: >> on=mount mount=/run/user/1000 : -a exit,always ... >> on=device device=/dev/sdd : -a exit,always ... >> >> The on-login event would simply watch the audit trail for any AUDIT_LOGIN >> events. That event can be parsed to get the new auid. If the auid matches >> any rules, then it will load them into the kernel. To remove the rules, >> we >> could watch for the AUDIT_USER_END event. The only issue is that we would >> need to track how many sessions the user has open and remove the rules >> only when the last session closes out. >> >> The rules for this might look something like this: >> on=login auid=1000 : -a exit,always ... >> >> The question is whether or not this should be done as part of the audit >> daemon or as a plugin for the audit daemon. One advantage of doing this >> as >> a plugin is that it will keep the audit daemon focused on getting events >> and distributing them. Any programming mistake in the plugin will crash >> it >> and not the daemon. The tradeoff is that it will get the event slightly >> after auditd sees it. This only matters for the on-login functionality. >> The device and mount events come from an entirely different source. And >> I'm sure that in every case, the program will react faster than a user >> possibily can winning the race evry time. >> >> Thoughts? > > Would bind mounts trigger these rules? I'm sitting next to a box with 10k > polyinstantiated bind mounts right now. If you do cat /proc/mounts do you see 10k entries?

And do you want them or do you think they are harmful?

-Steve