From: Petr Špaček <petr.spacek@nic.cz>
Date: Wed, 11 Mar 2020 15:46:18 +0000 (+0100)
Subject: debug: warn on qname letter case mismatch
X-Git-Tag: v5.1.0~26^2~14
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=173f29a4053d6d8e21a96a0a97d4819358748b5f;p=thirdparty%2Fknot-resolver.git

debug: warn on qname letter case mismatch

We de-randomize qname letter case very early so kr_pkt_text() should see
all lowercase. Any uppercase means mismatch.

I've considered moving debug print to an earlier place but this way it
is more visible so I like more.
---

diff --git a/lib/utils.c b/lib/utils.c
index 8c7cd89df..34f80cc5f 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -983,6 +983,21 @@ static char *print_section_opt(struct mempool *mp, char *endp, const knot_rrset_
 
 }
 
+/**
+ * Detect if qname contains an uppercase letter.
+ */
+static bool qname_has_uppercase(const knot_dname_t *qname) {
+	const int len = knot_dname_size(qname) - 1;  /* skip root label at the end */
+	for (int i = 1; i < len; ++i) {  /* skip first length byte */
+		/* Note: this relies on the fact that correct label lengths
+		 * can't pass this test by "luck" and that correctness
+		 * is checked earlier by packet parser. */
+		if (qname[i] >= 'A' && qname[i] <= 'Z')
+			return true;
+	}
+	return false;
+}
+
 char *kr_pkt_text(const knot_pkt_t *pkt)
 {
 	if (!pkt) {
@@ -1030,7 +1045,14 @@ char *kr_pkt_text(const knot_pkt_t *pkt)
 	if (qdcount == 1) {
 		KR_DNAME_GET_STR(qname, knot_pkt_qname(pkt));
 		KR_RRTYPE_GET_STR(rrtype, knot_pkt_qtype(pkt));
-		ptr = mp_printf_append(mp, ptr, ";; QUESTION SECTION\n%s\t\t%s\n", qname, rrtype);
+		const char *qnwarn;
+		if (qname_has_uppercase(knot_pkt_qname(pkt)))
+			qnwarn = \
+"; WARNING! Uppercase letters indicate positions with letter case mismatches!\n"
+";          Normally you should see all-lowercase qname here.\n";
+		else
+			qnwarn = "";
+		ptr = mp_printf_append(mp, ptr, ";; QUESTION SECTION\n%s%s\t\t%s\n", qnwarn, qname, rrtype);
 	} else if (qdcount > 1) {
 		ptr = mp_printf_append(mp, ptr, ";; Warning: unsupported QDCOUNT %hu\n", qdcount);
 	}