Messages in this thread | | | From | Christoph Rohland <> | Subject | Re: DoS using tmpfs | Date | 13 Jun 2001 09:04:51 +0200 |
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Hi Pavel,
On Fri, 8 Jun 2001, Pavel Roskin wrote: > Hello! > > It appears that a system with tmpfs mounted with the default (!!!) > parameters can be used by ordinary users to make the system > non-functional.
...
> 1) tmpfs, as opposed to ramfs doesn't limit the usage by > default. It's not a good default for a filesystem designed for > temporary files.
Yes, use the size parameter. And no, ramfs has no resource limits in the stock kernel at all. In -ac it limits to half the size of the physical RAM unconditionally. But that's not useful for tmpfs simce this uses swap also. So it is the admins task to add a size parameter. I would love to add a size paramater in percent of virtual memory but this would need some changes in the swapon/off coding.
> 2) Not delivering SIGINT to processes is probably not the best > behavior if the memory if low. However, one could argue that some > processes would use even more resources if they get control with > SIGINT. > > 3) All swap in the system was exhausted and yet tmpfs didn't return > ENOSPC to "dd".
That the kernel locks up is IMHO a mm fault. tmpfs allocates its pages with GFP_USER and will return an error if this fails. Apparently it never fails but locks up.
Greetings Christoph
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