Date: Mon, 2 Aug 2021 14:19:00 +0200 From: Michael Gmelin <freebsd@grem.de> To: jail@freebsd.org Subject: POSIX shared memory, jails, and (lack of) limits Message-ID: <20210802141900.069d0051@bsd64.grem.de>
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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 Best, Michael -- Michael Gmelin
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