The answer count is checked before the response question is parsed.
Most DNS servers return a truncated response without answers, so such
a response is classified as ANCOUNT_ZERO before the TC flag and
question type are examined. It increments the wrong counter and hides
the actual response status.
Move the empty-answer check after question parsing and TC handling.
Truncated SRV responses keep their existing partial-answer behavior.
This should be backported as far as 2.4.
---
src/resolvers.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/src/resolvers.c b/src/resolvers.c
index 06fb19c41..9f4e5fc0d 100644
--- a/src/resolvers.c
+++ b/src/resolvers.c
@@ -1091,10 +1091,6 @@ static int resolv_validate_dns_response(unsigned char
*resp, unsigned char *bufe
if (reader + 2 > bufend)
goto invalid_resp;
r_res->header.ancount = reader[0] * 256 + reader[1];
- if (r_res->header.ancount == 0) {
- cause = RSLV_RESP_ANCOUNT_ZERO;
- goto return_error;
- }
/* Check if too many records are announced */
if (r_res->header.ancount > max_answer_records)
@@ -1157,6 +1153,11 @@ static int resolv_validate_dns_response(unsigned char
*resp, unsigned char *bufe
goto return_error;
}
+ if (r_res->header.ancount == 0) {
+ cause = RSLV_RESP_ANCOUNT_ZERO;
+ goto return_error;
+ }
+
/* now parsing response records */
nb_saved_records = 0;
for (i = 0; i < r_res->header.ancount; i++) {
--
2.55.0
