Re: short read from /dev/urandom

["Theodore Ts'o" <tytso@mit.edu>]

On Fri, Jan 14, 2005 at 01:04:52PM -0800, Ulrich Drepper wrote:
> I'm concerned that there is isgnificant code out there relying on the 
> no-short-read promise.  And perhaps more importantly, other 
> implementations promise the same.
> 
> The code in question comes from a crypto library which is in wide use 
> (http://www.cryptopp.com) and it is using urandom under this assumption. 
>  I fear there is quite a bit more code like this out there.  Changing 
> the ABI after the fact is no good and dangerous in this case.
> 
> I know this is making the device special, but I really think the 
> no-short-reads property should be perserved for urandom.

Good point.  The fact that there are other implementations out there
which are doing this is a convincing argument.  

I am still a bit concerned still that a stupidly written program that
opens /dev/urandom (perhaps unwittingly) and tries to read a few
hundred megabytes will become uninterruptible until the read
completes, but I'm not sure it's worth it to but in some kludge that
says "break if there's a signal and count > 1 megabyte --- otherwise
we'll return soon enough".

						- Ted