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

On Wed 2014-07-23 14:10:16, Hannes Frederic Sowa wrote:

On Wed, Jul 23, 2014, at 13:52, George Spelvin wrote:

quoted

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.

quoted

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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