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)

When a dynamic NSS module is built and linked against a thread
library, it may pull in that thread library at run time. If the
process started out single-threaded, this could cause attempts to
release locks that do not exist. Guard against this possibility by
checking __isthreaded before invoking thread primitives.

A similar problem remains if the process is linked against one thread
library, but the NSS module is linked against another. This can only
be avoided by careful design of the NSS module.

Submitted by: Sean McNeil <sean@mcneil.com> (mostly; bugs are mine)

It was reported that when using nss_ldap, getgrent(3) would behave
incorrectly when encountering `large' groups (many members and/or many
long member names). The reporter tracked this down to the glibc NSS
module compatibility code (nss_compat.c): it would prematurely record
that a NSS module was finished iterating through its database in some
cases.

Two aspects are corrected:

1. nss_compat.c recorded that a NSS module was finished iterating
whenever the module reported something other than SUCCESS. The
correct logic is to continue iteration when the module reports
either SUCCESS or RETURN. The __nss_compat_getgrent_r and
__nss_compat_getpwent_r routines are updated to reflect this.

2. An internal helper macro __nss_compat_result is used to map glibc
NSS status codes to BSD NSS status codes (e.g. NSS_STATUS_SUCCESS ->
NS_SUCCESS). It provided the obvious mapping.

When a NSS routine is called with a too-small buffer, the
convention in the BSD NSS code is to report RETURN. (This is used
to implement reentrant APIs such as getpwnam_r(3).) However, the
convention in glibc for this case is to set errno = ERANGE and
overload TRYAGAIN. __nss_compat_result is updated to handle this
case.

PR: bin/60287
Reported by: Lachlan O'Dea <odela01@ca.com>

= Implement name service switch modules (NSS modules). NSS modules
may be built into libc (`static NSS modules') or dynamically loaded
via dlopen (`dynamic NSS modules'). Modules are loaded/initialized
at configuration time (i.e. when nsdispatch is called and nsswitch.conf
is read or re-read).

= Make the nsdispatch(3) core thread-safe.

= New status code for nsdispatch(3) `NS_RETURN', currently used to
signal ERANGE-type issues.

= syslog(3) problems, don't warn/err/abort.

= Try harder to avoid namespace pollution.

= Implement some shims to assist in porting NSS modules written for
the GNU C Library nsswitch interface.

Sponsored by: DARPA, Network Associates Laboratories