Subject: Re: [RFC] tcp: setsockopt congestion control autoload

From: Patrick McHardy <[email-masked]>
Date: Thu, 26 Oct 2006 01:21:46 +0200

Stephen Hemminger wrote:
> If user asks for a congestion control type with setsockopt() then it
> may be available as a module not included in the kernel already. 
> It should be autoloaded if needed.  This is done already when
> the default selection is change with sysctl, but not when application
> requests via sysctl.
> 
> Only reservation is are there any bad security implications from this?

There are already a quite large number of precedents for this, I think
this is one of the less questionable ones, the potential for (local)
damage is limited to minimal tcp_ca_find performance impact if I don't
miss anything (assuming no bugs in the modules that cause crashes
or something like that).

The in my opinion most questionable autoloading is in af_netlink BTW,
it will autoload any netlink provider with an appropriate module alias,
which could be just about anything (examples include conntrack, which
has performance and other side-effects, ULOG, which in turn loads
iptables, xfrm_user, connector, ...). Other autoloading is usually
limited to a clear scope of what might be affected.