mlock and jail

Xin LI delphij at
Thu Feb 2 22:01:42 UTC 2017

On Thu, Feb 2, 2017 at 1:28 PM, Bruno Lauzé <brunolauze at> wrote:
> But a simple user with no rights can mlock (64kb by default) why a jail would not be able?

No, I'm not, by any means, arguing against having jailed processes
being able to mlock(), I'm just saying that we should have more fine
grained control over it (a knob to allow system administrators to
tweak it would be a good start).


> From: Xin LI<mailto:delphij at>
> Sent: Thursday, February 2, 2017 1:13 PM
> To: Pavel Timofeev<mailto:timp87 at>
> Cc: Bruno Lauzé<mailto:brunolauze at>; freebsd-current<mailto:freebsd-current at>
> Subject: Re: mlock and jail
> On Thu, Feb 2, 2017 at 7:54 AM, Pavel Timofeev <timp87 at> wrote:
>> 2017-02-02 4:31 GMT+03:00 Xin LI <delphij at>:
>>> I like this idea.
>>> Note that potentially your patch would make it possible for a jailed
>>> root to DoS the whole system by locking too much of pages in memory.
>>> I think it would be sensible to provide a per-jail flag to enable
>>> doing it, or better, have some finer grained control (e.g. per jail
>>> quota of permitted locked pages).
>>> Why did the application want to lock pages in main memory, though?
>> For example, this secret management tool
>> wants to lock memory for
>> security (surprise) reason.
>> It's available as security/vault in our ports tree.
> No it's not surprise but overkill IMHO.  Here is why:
> Locking memory does prevent swapping, but in a typical multi-user
> system, if an attacker is already able to read swap (keep in mind that
> disks are by default owned by root and can not be read in a typical
> setup), then the administrator already have much bigger problem to
> worry about, and the attacker would have much more powerful tools to
> steal the secrets.
> Additionally, if one really cares about safety of swap, they should
> have used encrypted swap in the first place.  On FreeBSD, appending
> '.eli' to the swap device in fstab (e.g. /dev/ada0p3 ->
> /dev/ada0p3.eli) would automatically do one-time keyed swapping.
> Moreover, I don't think it's a good idea to use an application that
> advocates locking all memory that it owns for "security" reasons: if
> the application writer does not know which memory pages would contain
> sensitive information, good chances that the application writer have
> no idea what is privilege separation and the design they have created
> could be fundamentally flawed.
> Cheers,
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