propagate PAM crashes to PerSourcePenalties

If the PAM subprocess crashes, exit with a crash status that will be
picked up by the sshd(8) listener process where it can be used by
PerSourcePenalties to block the client. This is similar handling to
the privsep preauth process.

auth-pam.c

@@ -100,6 +100,7 @@
 #include "ssh-gss.h"
 #endif
 #include "monitor_wrap.h"
+#include "srclimit.h"
 
 extern ServerOptions options;
 extern struct sshbuf *loginmsg;
@@ -166,13 +167,13 @@ sshpam_sigchld_handler(int sig)
 			return;
 		}
 	}
-	if (WIFSIGNALED(sshpam_thread_status) &&
-	    WTERMSIG(sshpam_thread_status) == SIGTERM)
-		return;	/* terminated by pthread_cancel */
-	if (!WIFEXITED(sshpam_thread_status))
-		sigdie("PAM: authentication thread exited unexpectedly");
-	if (WEXITSTATUS(sshpam_thread_status) != 0)
-		sigdie("PAM: authentication thread exited uncleanly");
+	if (sshpam_thread_status == -1)
+		return;
+	if (WIFSIGNALED(sshpam_thread_status)) {
+		if (signal_is_crash(WTERMSIG(sshpam_thread_status)))
+			_exit(EXIT_CHILD_CRASH);
+	} else if (!WIFEXITED(sshpam_thread_status))
+		_exit(EXIT_CHILD_CRASH);
 }
 
 /* ARGSUSED */