On Mon, Aug 02, 2021 at 02:19:00PM +0200, Michael Gmelin wrote: > Hi, > > I've been playing a bit with POSIX shared memory and, unlike for SysV > shared memory, I couldn't find any way to limit its use by jails. > > First, I looked at racct/rctl, but there is no resource for POSIX shared > memory and memoryuse/vmemoryuse don't seem to have an effect (which > makes sense). > > Then I checked if there are jail parameters that could help, but there > doesn't seem to be anything like "allow.sysvshm" for POSIX shared > memory to limit access to the feature. > > So, unless I'm missing something, it seems like all jails on a system > have unlimited access to POSIX shared memory and therefore any single > jail can use up the jailhost's virtual memory until the jailhost comes > to a grinding halt. > > I wrote a little test program that keeps allocating POSIX shared memory > inside of a jail and it can easily bring the host down to its knees: > > login: Aug 2 12:12:09 test kernel: pid 11825 (getty), jid 0, uid 0, > was killed: out of swap space > Aug 2 12:12:10 test init[11827]: getty repeating too quickly on port > /dev/ttyu0, sleeping 30 secs > Aug 2 12:12:10 test kernel: pid 11826 (getty), jid 0, uid 0, was > killed: out of swap space
Posix shm is limited by the swap accounting. For non-jail consumers, it is per-uid RLIMIT_SWAP. I do not know if other mechanisms make RLIMIT_SWAP per-jail per-uid.
