Cuserid() is a security hole

[Karl Heuer]

The plot thickens.  In POSIX, cuserid() is required to use the *effective uid*
of the process.  The Rationale section does not comment on this inconsistency
with traditional implementations.

Moreover, POSIX getlogin() is supposed to return the login name associated
with the *controlling terminal*, not the tty on descriptor 0-2 as is commonly
implemented.  Since, as Guy points out, a program can't always find the true
name of its controlling terminal, it would seem that this requires either a
new system call, or else getlogin() should just give up and return NULL.

Karl W. Z. Heuer (ima!haddock!karl or karl at haddock.isc.com), The Walking Lint