Messages in this thread | | | Subject | Re: sunrpc port allocation and IANA reserved list | From | Ben Hutchings <> | Date | Tue, 10 Nov 2009 21:32:00 +0000 |
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On Tue, 2009-11-10 at 15:06 -0600, Chris Friesen wrote: > On 11/10/2009 02:26 PM, Trond Myklebust wrote: > > On Tue, 2009-11-10 at 12:37 -0600, Chris Friesen wrote: > >> On 11/10/2009 11:53 AM, Ben Hutchings wrote: > >>> On Tue, 2009-11-10 at 11:43 -0600, Chris Friesen wrote: > >> > >>>> Given that a userspace application can be stopped and restarted at any > >>>> time, and a sunrpc registration can happen at any time, what is the > >>>> expected mechanism to prevent the kernel from allocating a port for use > >>>> by sunrpc that reserved or well-known? > >>>> > >>>> Apparently Redhat and Debian have distro-specific ways of dealing with > >>>> this, but is there a standard solution? Should there be? > >>>> > >>>> The current setup seems suboptimal. > >>> > >>> I believe both RH and Debian are using the same implementation: > >>> <http://cyberelk.net/tim/software/portreserve/>. > >> > >> That helps with the startup case, but still leaves a possible hole if an > >> app using a fixed port number is restarted at runtime. During the > >> window where nobody is bound to the port, the kernel could randomly > >> assign it to someone else. > > > > Just use /proc/sys/sunrpc/{max,min}_resvport interface to restrict the > > range used to a safer one. That's what it is for...
Unless I'm much mistaken, that only affects in-kernel SunRPC users.
> What constitutes a "safer range"? IANA has ports assigned > intermittently all the way through the default RPC range. The largest > unassigned range is 922-988 (since 921 is used by lwresd). If someone > needs more than 66 ports, how are they supposed to handle it?
I'm sure we could afford 128 bytes for a blacklist of privileged ports. However, the problem is that there is no API for userland to request 'any free privileged port' - it has to just try binding to different ports until it finds one available. This means that the kernel can't tell whether a process is trying to allocate a specifically assigned port or whether the blacklist should be applied.
Ben.
-- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.
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