Messages in this thread |  | | Date | Sat, 31 Aug 2002 15:14:21 +0200 (CEST) | From | Krzysztof Benedyczak <> | Subject | Re: [PATCH] POSIX message queues |
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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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