pingpong: fix response cache memcpy overflow

Response data for a handle with a large buffer might be cached and then
used with the "closure" handle when it has a smaller buffer and then the
larger cache will be copied and overflow the new smaller heap based
buffer.

Reported-by: Dario Weisser
CVE: CVE-2018-1000300
Bug: https://curl.haxx.se/docs/adv_2018-82c2.htm

Change-Id: I02d35b9494356aaec1ca1f8eab0353a58c849e11

diff --git a/lib/pingpong.c b/lib/pingpong.c
index 438856a..ad370ee 100644 (file)
--- a/lib/pingpong.c
+++ b/lib/pingpong.c
@@ -304,7 +304,10 @@ CURLcode Curl_pp_readresp(curl_socket_t sockfd,
        * it would have been populated with something of size int to begin
        * with, even though its datatype may be larger than an int.
        */
-      DEBUGASSERT((ptr + pp->cache_size) <= (buf + data->set.buffer_size + 1));
+      if((ptr + pp->cache_size) > (buf + data->set.buffer_size + 1)) {
+        failf(data, "cached response data too big to handle");
+        return CURLE_RECV_ERROR;
+      }
       memcpy(ptr, pp->cache, pp->cache_size);
       gotbytes = (ssize_t)pp->cache_size;
       free(pp->cache);    /* free the cache */