s3: smbd: Chain code can return uninitialized memory when talloc buffer is grown.

Ensure we zero out unused grown area.

CVE-2017-15275

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13077

Signed-off-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(master): Tue Nov 21 19:42:22 CET 2017 on sn-devel-144

diff --git a/source3/smbd/srvstr.c b/source3/smbd/srvstr.c
index 56dceba8c6cb1c40391116643d1c1ddae00004a7..c2d70b32c32459df892c9b3268685065ef4b497a 100644 (file)
--- a/source3/smbd/srvstr.c
+++ b/source3/smbd/srvstr.c
@@ -110,6 +110,20 @@ ssize_t message_push_string(uint8_t **outbuf, const char *str, int flags)
                DEBUG(0, ("srvstr_push failed\n"));
                return -1;
        }
+
+       /*
+        * Ensure we clear out the extra data we have
+        * grown the buffer by, but not written to.
+        */
+       if (buf_size + result < buf_size) {
+               return -1;
+       }
+       if (grow_size < result) {
+               return -1;
+       }
+
+       memset(tmp + buf_size + result, '\0', grow_size - result);
+
        set_message_bcc((char *)tmp, smb_buflen(tmp) + result);
 
        *outbuf = tmp;