Re: [PATCH, RFC] random: introduce getrandom(2) system call

[Pavel Machek <pavel@ucw.cz>]

On Wed 2014-07-23 14:10:16, Hannes Frederic Sowa wrote:
> 
> 
> On Wed, Jul 23, 2014, at 13:52, George Spelvin wrote:
> > I keep wishing for a more general solution.  For example, some way to
> > have a "spare" extra fd that could be accessed with a special O_NOFAIL
> > flag.
> > 
> > That would allow any number of library functions to not fail, such as
> > logging from nasty corner cases.
> > 
> > But you'd have to provide one per thread, and block non-fatal signals
> > while it was open, so you don't get reentrancy problems.  Ick.
> > 
> > 
> > This overly-specialized system call (and worse yet, a blocking
> > system call that you can't put into a poll() loop) just feels ugly
> > to me.  Is it *absolutely* necessary?
> 
> One point that often came up besides fd exhaustion is missing
> /dev/u?random device nodes in chroot environments.

>From the maillist discussion, it seems you sometimes _want_
/dev/random not to be present.

For example you want to trace exactly the same path through malware
every time.

> > For example, how about simply making getentropy() a library function that
> > aborts if it can't open /dev/urandom?  If you're suffering fd exhaustion,
> > you're being DoSed already.
> 
> Maybe applications want to mitigate fd exhaustion.

Dunno. Will we add special read_passwd() syscall that reads just
/etc/passwd, to allow uid<->name resolution without available FDs?

I like the library function suggestion, this should not need a new
syscall.

And btw -- compatibility with getentropy() is _not_ going to be easy,
if they have different blocking / partial read / signals policy.

									Pavel
-- 
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