dnsproxy: Add reply host part length checking

Check that the first part of the name is not of zero length before
attempting to calculate the length of the domain part. Also ensure
the domain lenght checking does not run outside of the receive
buffer.

Also add debug messages for ids and lengths in order to pinpoint
any possible problems.

diff --git a/src/dnsproxy.c b/src/dnsproxy.c
index 2a2e52c..17d9a20 100644 (file)
--- a/src/dnsproxy.c
+++ b/src/dnsproxy.c
@@ -1570,6 +1570,9 @@ static int ns_resolv(struct server_data *server, struct request_data *req,
                        alt[1] = req_len & 0xff;
                }
 
+               DBG("req %p dstid 0x%04x altid 0x%04x", req, req->dstid,
+                               req->altid);
+
                err = send(sk, alt, req->request_len + domlen, MSG_NOSIGNAL);
                if (err < 0)
                        return -EIO;
@@ -1611,7 +1614,8 @@ static int forward_dns_reply(unsigned char *reply, int reply_len, int protocol,
        if (req == NULL)
                return -EINVAL;
 
-       DBG("id 0x%04x rcode %d", hdr->id, hdr->rcode);
+       DBG("req %p dstid 0x%04x altid 0x%04x rcode %d",
+                       req, req->dstid, req->altid, hdr->rcode);
 
        ifdata = req->ifdata;
 
@@ -1627,17 +1631,25 @@ static int forward_dns_reply(unsigned char *reply, int reply_len, int protocol,
                 * remove it before forwarding the reply.
                 */
                if (req->append_domain == TRUE) {
+                       unsigned int domain_len = 0;
                        unsigned char *ptr;
                        uint8_t host_len;
-                       unsigned int domain_len;
+                       unsigned int header_len;
 
                        /*
                         * ptr points to the first char of the hostname.
                         * ->hostname.domain.net
                         */
-                       ptr = reply + offset + sizeof(struct domain_hdr);
+                       header_len = offset + sizeof(struct domain_hdr);
+                       ptr = reply + header_len;
                        host_len = *ptr;
-                       domain_len = strlen((const char *)ptr + host_len + 1);
+                       if (host_len > 0)
+                               domain_len = strnlen((const char *)ptr + 1 +
+                                               host_len,
+                                               reply_len - header_len);
+
+
+                       DBG("host len %d domain len %d", host_len, domain_len);
 
                        /*
                         * Remove the domain name and replace it by the end
@@ -1657,7 +1669,7 @@ static int forward_dns_reply(unsigned char *reply, int reply_len, int protocol,
                                 */
                                memmove(ptr + host_len + 1,
                                        ptr + host_len + domain_len + 1,
-                                       reply_len - (ptr - reply + domain_len));
+                                       reply_len - header_len - domain_len);
 
                                reply_len = reply_len - domain_len;
                        }