log: Fall back to syslog+vsnprintf if vsyslog is not available

On some platforms, like HP-UX, even vsyslog is not available. In this
case, we fall back to printing the message with vsnprintf and then
logging the message with syslog.

configure.ac

@@ -109,7 +109,7 @@ save_LIBS="$LIBS"
 LIBS="$PAM_LIBS"
 
 dnl Check for optional PAM fnuctions
-AC_CHECK_FUNCS(pam_syslog pam_vsyslog)
+AC_CHECK_FUNCS(vsyslog pam_syslog pam_vsyslog)
 
 dnl restore LIBS
 LIBS="$save_LIBS"

src/pam_hbac_compat.h

@@ -71,6 +71,14 @@ do {                             \
 # include <security/openpam.h>
 #endif /* HAVE_SECURITY_OPENPAM_H */
 
+#ifndef HAVE_VSYSLOG
+#define vsyslog(priority, fmt, vargs) do { \
+    char _vsyslog_msg[1024];                                    \
+    vsnprintf(_vsyslog_msg, sizeof(_vsyslog_msg), fmt, vargs);  \
+    syslog(level, "%s", _vsyslog_msg);                          \
+} while(0);
+#endif /* HAVE_VSYSLOG */
+
 #ifndef HAVE_PAM_VSYSLOG
 #define pam_vsyslog(pamh, priority, fmt, vargs) \
     vsyslog((priority), (fmt), (vargs))