Description of problem:
Postfix tlsmgr dies with permission error, and that can DOS the mail system.

Version-Release number of selected component (if applicable):
postfix-2.5.1-2.fc9.i386

How reproducible:
yes, I assume

Steps to Reproduce:
1. Mail works with the following in Fedora 8 postfix main.cf:
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_type = cyrus
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt
2. upgrade to Fedora 9
3. can't send mail
  
Actual results:
May 20 00:47:39 localhost postfix/master[14239]: warning: process
/usr/libexec/postfix/tlsmgr pid 14513 exit status 1
May 20 00:47:39 localhost postfix/master[14239]: warning:
/usr/libexec/postfix/tlsmgr: bad command startup -- throttling
May 20 00:48:39 localhost postfix/tlsmgr[14562]: fatal: tls_prng_exch_open:
cannot open PRNG exchange file /var/lib/postfix/prng_exch: Permission denied
May 20 00:48:40 localhost postfix/master[14239]: warning: process
/usr/libexec/postfix/tlsmgr pid 14562 exit status 1
May 20 00:48:40 localhost postfix/master[14239]: warning:
/usr/libexec/postfix/tlsmgr: bad command startup -- throttling

Additional info:
http://mail-index.netbsd.org/pkgsrc-users/2008/03/14/msg000561.html claims that
it has been solved in 2.5.1nb1

Problem might be related to issue 437042 and how it is solved.

A workaround is to add
tls_random_exchange_name = /var/spool/postfix/saved/prng_exch
which makes it work for me ... but I don't know if saved is the right place.

And I don't know what the real problem really is. But I think it might be worth
a backport of upgrade.