mlock(2) for ordinary users

Currently mlock() and munlock() are restricted to the root user -
which prevents an ordinary user locking their process into RAM to the
detriment of the system as a whole. Whilst this is a valid concern,
there are good security reasons for allowing a user to lock small
amounts of memory (a few pages) to ensure that sensitive information
(private keys, passwords etc) don't wind up on swap devices.

There is a resource limit for locked pages (RLIMIT_MEMLOCK) and,
despite the man page, a quick look at the code implies that it really
is honoured. Could someone with more VM-foo please confirm whether
the last line of the man page is still correct.

I would like to suggest that the suser() tests in mlock() and
munlock() be removed and the default RLIMIT_MEMLOCK is reduced from
infinity to (say) 1. The only gotcha I can see is that lots of
sysctl() functions use RLIMIT_MEMLOCK via sysctl_wire_old_buffer()
and vslock().

Comments please.
--
Peter Jeremy

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