openssh unix dev - May 2022 - PrintLastLog fails on systems without lastlog but with utmpx

>From FreeBSD PR 209441. configure sets DISABLE_LASTLOG if we do not
have lastlog.ll_line:

AC_CHECK_MEMBER([struct lastlog.ll_line], [], [
    if test x$SKIP_DISABLE_LASTLOG_DEFINE != "xyes" ; then
        AC_DEFINE([DISABLE_LASTLOG])
    fi
        ], [

However DISABLE_LASTLOG disables support for PrintLastLog altogether
-- from servconf.c:

#ifdef DISABLE_LASTLOG
        { "printlastlog", sUnsupported, SSHCFG_GLOBAL },
#else
        { "printlastlog", sPrintLastLog, SSHCFG_GLOBAL },
#endif

In getlast_entry() DISABLE_LASTLOG disables use of wtmp and wtmpx, but
not utmpx. DISABLE_LASTLOG seems to be intended to mean disable last
login functionality altogether, and disable use of specifically
utmp/lastlog, in different locations.

It seems like (for consistency with --disable-utmp, --disable-utmpx,
--disable-wtmp, --disable-wtmpx) DISABLE_LASTLOG should refer only to
lastlog specifically, not last login functionality in general. Thus,
servconf should probably be:

#if defined(DISABLE_LASTLOG) && defined(DISABLE_UTMP) &&
defined(DISABLE_UTMPX) &&...
        { "printlastlog", sUnsupported, SSHCFG_GLOBAL },
#else
        { "printlastlog", sPrintLastLog, SSHCFG_GLOBAL },
#endif

and getlast_entry() should move the wtmp/wtmpx cases out of
!defined(DISABLE_LASTLOG).

On Wed, 18 May 2022 at 14:13, Ed Maste <emaste at freebsd.org>
wrote:
>
> From FreeBSD PR 209441. configure sets DISABLE_LASTLOG if we do not
> have lastlog.ll_line:
>
> AC_CHECK_MEMBER([struct lastlog.ll_line], [], [
>     if test x$SKIP_DISABLE_LASTLOG_DEFINE != "xyes" ; then
>         AC_DEFINE([DISABLE_LASTLOG])
>     fi
>         ], [
>
> However DISABLE_LASTLOG disables support for PrintLastLog altogether
> -- from servconf.c:
>
> #ifdef DISABLE_LASTLOG
>         { "printlastlog", sUnsupported, SSHCFG_GLOBAL },
> #else
>         { "printlastlog", sPrintLastLog, SSHCFG_GLOBAL },
> #endif
>
> In getlast_entry() DISABLE_LASTLOG disables use of wtmp and wtmpx, but
> not utmpx. DISABLE_LASTLOG seems to be intended to mean disable last
> login functionality altogether, and disable use of specifically
> utmp/lastlog, in different locations.
This is still the case -- DISABLE_LASTLOG can be set if we do not want
lastlog functionality, but it is automatically set by configure if we
don't have lastlog.ll_line:

AC_CHECK_MEMBER([struct lastlog.ll_line], [], [
    if test x$SKIP_DISABLE_LASTLOG_DEFINE != "xyes" ; then
        AC_DEFINE([DISABLE_LASTLOG])
    fi

elsewhere we explicitly do not set DISABLE_LASTLOG if a lastlog file
cannot be found, with a comment that wtmp/wtmpx would not be tested:

                if test -z "$conf_lastlog_location"; then
                        AC_MSG_WARN([** Cannot find lastlog **])
                        dnl Don't define DISABLE_LASTLOG - that means
we don't try wtmp/wtmpx
                fi

and there's a special case SCO OpenServer 5.x:

        SKIP_DISABLE_LASTLOG_DEFINE=yes

to avoid the lastlog.ll_line test.

As a workaround to fix this for FreeBSD I just added SKIP_DISABLE_LASTLOG_DEFINE
https://cgit.freebsd.org/src/commit/?id=170511589e4d15a27ee92979691cfc1b26929bb7
but this needs a proper fix, presumably by splitting DISABLE_LASTLOG in two.