mime: check Curl_rand_hex's return code

Bug: https://curl.haxx.se/mail/archive-2018-07/0015.html
Reported-by: Jeffrey Walton
Closes #2795

diff --git a/lib/mime.c b/lib/mime.c
index fd7beb9a4e523703d8bcd561100c6b44865a3e3b..ca492d11ae984365be507a1d3fb4fba03f858cf4 100644 (file)
--- a/lib/mime.c
+++ b/lib/mime.c
@@ -1228,8 +1228,13 @@ curl_mime *curl_mime_init(struct Curl_easy *easy)
     }
 
     memset(mime->boundary, '-', 24);
-    Curl_rand_hex(easy, (unsigned char *) mime->boundary + 24,
-                  MIME_RAND_BOUNDARY_CHARS + 1);
+    if(Curl_rand_hex(easy, (unsigned char *) mime->boundary + 24,
+                     MIME_RAND_BOUNDARY_CHARS + 1)) {
+      /* failed to get random separator, bail out */
+      free(mime->boundary);
+      free(mime);
+      return NULL;
+    }
     mimesetstate(&mime->state, MIMESTATE_BEGIN, NULL);
   }