Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Do not gratuitously fail *env(3) operations due to corrupt ('='-less)
**environ entries. This puts non-getenv(3) operations in line with
getenv(3) in that bad environ entries do not cause all operations to
fail. There is still some inconsistency in that getenv(3) in the
absence of any environment-modifying operation does not emit corrupt
environ entry warnings.

I also fixed another inconsistency in getenv(3) where updating the
global environ pointer would not be reflected in the return values.
It would have taken an intermediary setenv(3)/putenv(3)/unsetenv(3)
in order to see the change.

Detect if the application has cleared the environ variable by setting
the first value (environ[0]) to NULL. This is in addition to the
current detection of environ being replaced, which includes being set to
NULL. Without this fix, the environment is not truly wiped, but appears
to be by getenv() until an *env() call is made to alter the enviroment.

This change is necessary to support those applications that use this
method for clearing environ such as Dovecot and Postfix. Applications
such as Sendmail and the base system's env replace environ (already
detected). While neither of these methods are defined by SUSv3, it is
best to support them due to historic reasons and in lieu of a clean,
defined method.

Add extra units tests for clearing environ using four different methods:
1. Set environ to NULL pointer.
2. Set environ[0] to NULL pointer.
3. Set environ to calloc()'d NULL-terminated array.
4. Set environ to static NULL-terminated array.

Noticed by: Timo Sirainen

MFC after: 3 days

Fix whitespace.

Differentiate in the tests against getenv() between an empty string and a
NULL by having the test program return *NULL* for NULL's (no existing
variable) instead of an empty string (variable with empty value).

Remove a dereference. It was unintended and a no-op.

Use the correct value of errno. Although the errno value passed into
printf() follows the *env() call, it is not guaranteed to be the errno
from that call. When I wrote the regression tester, the environment I
used did pass the errno from the call. Consolidate the print for the
return code and errno into a function in the process of fixing this.

Approved by: wes (mentor)

Added environ-replacement detection. For programs that "clean" (i.e., su)
or replace (i.e., zdump) the environment after a call to setenv(), putenv()
or unsetenv() has been made, a few changes were made.
- getenv() will return the value from the new environ array.
- setenv() was split into two functions: __setenv() which is most of the
previous setenv() without checks on the name and setenv() which
contains the checks before calling __setenv().
- setenv(), putenv() and unsetenv() will unset all previous values and
call __setenv() on all entries in the new environ array which in turn
adds them to the end of the envVars array. Calling __setenv() instead
of setenv() is done to avoid the temporary replacement of the '=' in a
string with a NUL byte. Some strings may be read-only data.

Added more regression checks for clearing the environment array.

Replaced gettimeofday() with getrusage() in timing regression check for
better accuracy.

Fixed an off-by-one bug in __remove_putenv() in the use of memmove(). This
went unnoticed due to the allocation of double the number of environ
entries when building envVars.

Fixed a few spelling mistakes in the comments.

Reviewed by: ache
Approved by: wes
Approved by: re (kensmith)

Significantly reduce the memory leak as noted in BUGS section for
setenv(3) by tracking the size of the memory allocated instead of using
strlen() on the current value.

Convert all calls to POSIX from historic BSD API:
- unsetenv returns an int.
- putenv takes a char * instead of const char *.
- putenv no longer makes a copy of the input string.
- errno is set appropriately for POSIX. Exceptions involve bad environ
variable and internal initialization code. These both set errno to
EFAULT.

Several patches to base utilities to handle the POSIX changes from
Andrey Chernov's previous commit. A few I re-wrote to use setenv()
instead of putenv().

New regression module for tools/regression/environ to test these
functions. It also can be used to test the performance.

Bump __FreeBSD_version to 700050 due to API change.

PR: kern/99826
Approved by: wes
Approved by: re (kensmith)