On Tuesday, May 12, 2020 8:31:45 PM EDT Joe Nall wrote: > > On May 12, 2020, at 7:22 PM, Steve Grubb <[email protected]> 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 -- Linux-audit mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-audit
