pbrd: Fix nearly impossible truncation

Since we are writing into the name field which is PBR_MAP_NAMELEN
size, we are expecting this to field to be at max 100 bytes.
Newer compilers understand that the %s portion may be up to
100 bytes( because of the size of the string.  The %u portion
is expected to be 10 bytes.  So in `theory` there are situations
where we might truncate.  The reality this is never going to
happen( who is going to create a nexthop group name that is
over say 30 characters? ).  As such we are expecting the
calling function to subtract 10 from the size_t l before
we pass it in to get around this new gcc fun.

Fixes: #2163
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

pbrd/pbr_nht.c

@@ -470,6 +470,18 @@ void pbr_nht_change_group(const char *name)
 	pbr_nht_install_nexthop_group(pnhgc, nhgc->nhg);
 }
 
+/*
+ * Since we are writing into the name field which is PBR_MAP_NAMELEN
+ * size, we are expecting this to field to be at max 100 bytes.
+ * Newer compilers understand that the %s portion may be up to
+ * 100 bytes( because of the size of the string.  The %u portion
+ * is expected to be 10 bytes.  So in `theory` there are situations
+ * where we might truncate.  The reality this is never going to
+ * happen( who is going to create a nexthop group name that is
+ * over say 30 characters? ).  As such we are expecting the
+ * calling function to subtract 10 from the size_t l before
+ * we pass it in to get around this new gcc fun.
+ */
 char *pbr_nht_nexthop_make_name(char *name, size_t l,
 				uint32_t seqno, char *buffer)
 {
@@ -485,7 +497,7 @@ void pbr_nht_add_individual_nexthop(struct pbr_map_sequence *pbrms)
 	struct pbr_nexthop_cache lookup;
 
 	memset(&find, 0, sizeof(find));
-	pbr_nht_nexthop_make_name(pbrms->parent->name, PBR_MAP_NAMELEN,
+	pbr_nht_nexthop_make_name(pbrms->parent->name, PBR_MAP_NAMELEN - 10,
 				  pbrms->seqno, find.name);
 	if (!pbrms->internal_nhg_name)
 		pbrms->internal_nhg_name = XSTRDUP(MTYPE_TMP, find.name);

pbrd/pbr_vty.c

@@ -269,7 +269,7 @@ DEFPY(pbr_map_nexthop, pbr_map_nexthop_cmd,
 	if (pbrms->nhg)
 		nh = nexthop_exists(pbrms->nhg, &nhop);
 	else {
-		char buf[100];
+		char buf[PBR_MAP_NAMELEN];
 
 		if (no) {
 			vty_out(vty, "No nexthops to delete");
@@ -280,7 +280,7 @@ DEFPY(pbr_map_nexthop, pbr_map_nexthop_cmd,
 		pbrms->internal_nhg_name =
 			XSTRDUP(MTYPE_TMP,
 				pbr_nht_nexthop_make_name(pbrms->parent->name,
-							  PBR_MAP_NAMELEN,
+							  PBR_MAP_NAMELEN - 10,
 							  pbrms->seqno,
 							  buf));
 		nh = NULL;