On Fri, Nov 29, 2024 at 08:32:28AM -0700, Theo de Raadt wrote:
> I fear that the -x option will eventually become a useful crutch to
> block other behaviours.  Maybe this should be -0, to be more be
> explicit about this AS0 issue.  In the manual page, AS0 support being
> tied to a specific flag called -0 makes it easier to make the public
> aware of this problem and the decision for AS0 non-support.

How about

Index: extern.h
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/extern.h,v
diff -u -p -r1.233 extern.h
--- extern.h	26 Nov 2024 13:59:09 -0000	1.233
+++ extern.h	30 Nov 2024 13:00:41 -0000
@@ -663,6 +663,7 @@ extern int noop;
 extern int filemode;
 extern int excludeaspa;
 extern int experimental;
+extern int includeas0;
 extern const char *tals[];
 extern const char *taldescs[];
 extern unsigned int talrepocnt[];
Index: main.c
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/main.c,v
diff -u -p -r1.275 main.c
--- main.c	21 Nov 2024 13:32:27 -0000	1.275
+++ main.c	30 Nov 2024 13:00:41 -0000
@@ -69,6 +69,7 @@ int	verbose;
 int	noop;
 int	excludeaspa;
 int	filemode;
+int	includeas0;
 int	shortlistmode;
 int	rrdpon = 1;
 int	repo_timeout;
@@ -1014,8 +1015,12 @@ main(int argc, char *argv[])
 	    "proc exec unveil", NULL) == -1)
 		err(1, "pledge");
 
-	while ((c = getopt(argc, argv, "Ab:Bcd:e:fH:jmnoP:Rs:S:t:T:vVx")) != -1)
+	while ((c =
+	    getopt(argc, argv, "0Ab:Bcd:e:fH:jmnoP:Rs:S:t:T:vVx")) != -1)
 		switch (c) {
+		case '0':
+			includeas0 = 1;
+			break;
 		case 'A':
 			excludeaspa = 1;
 			break;
@@ -1552,7 +1557,7 @@ main(int argc, char *argv[])
 
 usage:
 	fprintf(stderr,
-	    "usage: rpki-client [-ABcjmnoRVvx] [-b sourceaddr] [-d cachedir]"
+	    "usage: rpki-client [-0ABcjmnoRVvx] [-b sourceaddr] [-d cachedir]"
 	    " [-e rsync_prog]\n"
 	    "                   [-H fqdn] [-P epoch] [-S skiplist] [-s timeout]"
 	    " [-T table]\n"
Index: output.c
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/output.c,v
diff -u -p -r1.33 output.c
--- output.c	22 Feb 2024 12:49:42 -0000	1.33
+++ output.c	30 Nov 2024 13:00:41 -0000
@@ -82,6 +82,49 @@ static int	 output_finish(FILE *);
 static void	 sig_handler(int);
 static void	 set_signal_handler(void);
 
+/*
+ * Detect & reject so-called "AS0 TALs".
+ * AS0 TALs are TALs where for each and every subordinate ROA the asID field
+ * set to 0. Such TALs introduce operational risk, as they change the fail-safe
+ * from 'fail-open' to 'fail-closed'. Some context:
+ *     https://lists.afrinic.net/pipermail/rpd/2021/013312.html
+ *     https://lists.afrinic.net/pipermail/rpd/2021/013314.html
+ */
+static void
+prune_as0_tals(struct vrp_tree *vrps)
+{
+	struct vrp *v, *tv;
+	int talid;
+	int is_as0_tal[TALSZ_MAX] = { 0 };
+
+	for (talid = 0; talid < talsz; talid++)
+		is_as0_tal[talid] = 1;
+
+	if (includeas0)
+		return;
+
+	RB_FOREACH(v, vrp_tree, vrps) {
+		if (v->asid != 0)
+			is_as0_tal[v->talid] = 0;
+	}
+
+	for (talid = 0; talid < talsz; talid++) {
+		if (is_as0_tal[talid]) {
+			warnx("%s: Detected AS0 TAL, pruning associated VRPs",
+			    taldescs[talid]);
+		}
+	}
+
+	RB_FOREACH_SAFE(v, vrp_tree, vrps, tv) {
+		if (is_as0_tal[v->talid]) {
+			RB_REMOVE(vrp_tree, vrps, v);
+			free(v);
+		}
+	}
+
+	/* XXX: update talstats? */
+}
+
 int
 outputfiles(struct vrp_tree *v, struct brk_tree *b, struct vap_tree *a,
     struct vsp_tree *p, struct stats *st)
@@ -90,6 +133,8 @@ outputfiles(struct vrp_tree *v, struct b
 
 	atexit(output_cleantmp);
 	set_signal_handler();
+
+	prune_as0_tals(v);
 
 	for (i = 0; outputs[i].name; i++) {
 		FILE *fout;
Index: rpki-client.8
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/rpki-client.8,v
diff -u -p -r1.113 rpki-client.8
--- rpki-client.8	4 Nov 2024 11:39:12 -0000	1.113
+++ rpki-client.8	30 Nov 2024 13:00:41 -0000
@@ -22,7 +22,7 @@
 .Nd RPKI validator to support BGP routing security
 .Sh SYNOPSIS
 .Nm
-.Op Fl ABcjmnoRVvx
+.Op Fl 0ABcjmnoRVvx
 .Op Fl b Ar sourceaddr
 .Op Fl d Ar cachedir
 .Op Fl e Ar rsync_prog
@@ -63,6 +63,10 @@ in various formats.
 .Pp
 The options are as follows:
 .Bl -tag -width Ds
+.It Fl 0
+Include potentially hazardous AS0 TALs in the output files.
+AS0 TALs are not recommended for automatic filtering of BGP routes.
+The default is not to include them.
 .It Fl A
 Exclude the ASPA-set from the output files that support it (JSON and
 OpenBGPD).