If user resolver tries to resolve a name without domain part,
then glibc gethostbyname() expects that returned answers do
not contain any domain name either. The getaddrinfo() works
differently and accepts FQDN in answers.
---
src/dnsproxy.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 66 insertions(+), 6 deletions(-)
diff --git a/src/dnsproxy.c b/src/dnsproxy.c
index 77aabd7..2bf1690 100644
--- a/src/dnsproxy.c
+++ b/src/dnsproxy.c
@@ -1877,6 +1877,45 @@ out:
return NULL;
}
+static int strip_domains(char *name, char *answers, int maxlen)
+{
+ uint16_t data_len;
+ int name_len = strlen(name);
+ char *ptr, *start = answers, *end = answers + maxlen;
+
+ while (maxlen > 0) {
+ ptr = strstr(answers, name);
+ if (ptr) {
+ char *domain = ptr + name_len;
+
+ if (*domain) {
+ int domain_len = strlen(domain);
+
+ memmove(answers + name_len,
+ domain + domain_len,
+ end - (domain + domain_len));
+
+ end -= domain_len;
+ maxlen -= domain_len;
+ }
+ }
+
+ answers += strlen(answers) + 1;
+ answers += 2 + 2 + 4; /* skip type, class and ttl fields */
+
+ data_len = answers[0] << 8 | answers[1];
+ answers += 2; /* skip the length field */
+
+ if (answers + data_len > end)
+ return -EINVAL;
+
+ answers += data_len;
+ maxlen -= answers - ptr;
+ }
+
+ return end - start;
+}
+
static int forward_dns_reply(unsigned char *reply, int reply_len, int protocol,
struct server_data *data)
{
@@ -1972,6 +2011,8 @@ static int forward_dns_reply(unsigned char *reply, int
reply_len, int protocol,
*/
if (domain_len > 0) {
int len = host_len + 1;
+ int new_len, fixed_len;
+ char *answers;
/*
* First copy host (without domain name) into
@@ -1994,6 +2035,8 @@ static int forward_dns_reply(unsigned char *reply, int
reply_len, int protocol,
*/
ptr += NS_QFIXEDSZ;
uptr += NS_QFIXEDSZ;
+ answers = uptr;
+ fixed_len = answers - uncompressed;
/*
* We then uncompress the result to buffer
@@ -2025,22 +2068,39 @@ static int forward_dns_reply(unsigned char *reply, int
reply_len, int protocol,
goto out;
/*
+ * The uncompressed buffer now contains almost
+ * valid response. Final step is to get rid of
+ * the domain name because at least glibc
+ * gethostbyname() implementation does extra
+ * checks and expects to find an answer without
+ * domain name if we asked a query without
+ * domain part. Note that glibc getaddrinfo()
+ * works differently and accepts FQDN in answer
+ */
+ new_len = strip_domains(uncompressed, answers,
+ uptr - answers);
+ if (new_len < 0) {
+ DBG("Corrupted packet");
+ return -EINVAL;
+ }
+
+ /*
* Because we have now uncompressed the answers
- * we must create a bigger buffer to hold all
- * that data.
+ * we might have to create a bigger buffer to
+ * hold all that data.
*/
- new_reply = g_try_malloc(header_len +
- uptr - uncompressed);
+ reply_len = header_len + new_len + fixed_len;
+
+ new_reply = g_try_malloc(reply_len);
if (!new_reply)
return -ENOMEM;
memcpy(new_reply, reply, header_len);
memcpy(new_reply + header_len, uncompressed,
- uptr - uncompressed);
+ new_len + fixed_len);
reply = new_reply;
- reply_len = header_len + uptr - uncompressed;
}
}
--
1.8.3.1
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