Date: Mon, 2 Aug 2021 22:03:27 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Michael Gmelin <freebsd@grem.de> Cc: jail@freebsd.org Subject: Re: POSIX shared memory, jails, and (lack of) limits Message-ID: <YQhBf17Sgwx91l/z@kib.kiev.ua> In-Reply-To: <EF1E80B4-684B-4698-A971-F637F0D726B4@grem.de> References: <YQf5ZNUV6hVm5gOK@kib.kiev.ua> <EF1E80B4-684B-4698-A971-F637F0D726B4@grem.de>
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On Mon, Aug 02, 2021 at 05:06:43PM +0200, Michael Gmelin wrote: > > > > On 2. Aug 2021, at 15:56, Konstantin Belousov <kostikbel@gmail.com> wrote: > > > > 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. > > Unfortunately it seems like POSIX shared memory is not linked to the jail it was created in (we discussed this on this list in June and I created a few PRs about that), so per jail rctl rules don’t apply (and limiting uid 0 won’t have the desired effect ^_^). > In what sense 'not linked'? The backing vm_object is created with the current process credentials, which are jailed if creator belongs to a jail.
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