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SubjectRe: [PATCH] POSIX message queues

On Sat, 31 Aug 2002 pwaechtler@mac.com wrote:
> > The mq_maxmsg and mq_msgsize members of the mq_attr structure required
> > if O_CREAT is passed to mq_open() ensure that an implementation can
> > prevent the kernel memory DoS you mention: a malicious application can
> > only fill up the MQ memory.
> And how many mqueues am I allowed to create?
> You would need an extra resource limit for that.

Some explanation about limits:
1) POSIX states about following limits:

You can specify when creating a new queue mq_maxmsg (max number of mes. in
this queue) and mq_msgsize (max mes. size). Values of those parameters are
limited by MQ_MAXMSG and MQ_MSGSIZE. Defaults are 40 and 16384, but you
can change them. Max number of queues (in system) is limited by MQ_MAX
(default=64). Anyway the problem is how to, keeping this constants at
sensible level, prevent from DOS. (40*16384*64= ca 40Mb)

So we added
2) non-POSIX limit:

MQ_MAXSYSSIZE which limits space used by all messages (NOT queues) system
wide. Maybe it isn't POSIX but useful I think. Default is 1Mb. It can be
given MQ_MAX*MQ_MAXMSG*MQ_MAXSIZE value; then it do nothing => and
you have only POSIX limits if you want so.

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