smtp: use the upload buffer size for scratch buffer malloc

... not the read buffer size, as that can be set smaller and thus cause
a buffer overflow! CVE-2018-0500

Reported-by: Peter Wu
Bug: https://curl.haxx.se/docs/adv_2018-70a2.html

Backported patch details:-

Link: https://github.com/curl/curl/commit/ba1dbd78e5f1e.patch
Change-Id: I5e6572de38862229fa319ce10c0d571e9e5a3543
Signed-off-by: Nishant Chaprana <n.chaprana@samsung.com>

diff --git a/lib/smtp.c b/lib/smtp.c
index 3f3b45a..400ad54 100644 (file)
--- a/lib/smtp.c
+++ b/lib/smtp.c
@@ -1563,13 +1563,14 @@ CURLcode Curl_smtp_escape_eob(struct connectdata *conn, const ssize_t nread)
   if(!scratch || data->set.crlf) {
     oldscratch = scratch;
 
-    scratch = newscratch = malloc(2 * data->set.buffer_size);
+    scratch = newscratch = malloc(2 * UPLOAD_BUFSIZE);
     if(!newscratch) {
       failf(data, "Failed to alloc scratch buffer!");
 
       return CURLE_OUT_OF_MEMORY;
     }
   }
+  DEBUGASSERT(UPLOAD_BUFSIZE >= nread);
 
   /* Have we already sent part of the EOB? */
   eob_sent = smtp->eob;