Description of problem:

Version 0.3 of GNU ed replaced use of unsecure mktemp() followed
by fopen() in buf.c:open_sbuf() with tmpnam(). The former construction
is vulnerable to race condition, where a malicous user can create
the temporary file between two function calls, as they are non-atomic,
and then either read or write the contents of the file, or make it
a symbolic link to a file owned by the victim resulting in its overite.

Version-Release number of selected component (if applicable):

GNU ed 0.2, in RHEL{2.1,3,4,5} and FC{5,6}

How reproducible:

Time-dependent race condition, very unlikely.

Steps to Reproduce:
1. Attempt to guess the filename returned by mktemp() and attempt
create it while being schelduled between mktemp() and fopen() calls.