upstream commit

Add some unsigned overflow checks for extra_pad. None of
these are reachable with the amount of padding that we use internally.
bz#2566, pointed out by Torben Hansen. ok markus@

Upstream-ID: 4d4be8450ab2fc1b852d5884339f8e8c31c3fd76

1 files changed, 15 insertions, 5 deletions

diff --git a/packet.c b/packet.c
index 3810f1128..7290fc714 100644
--- a/packet.c
+++ b/packet.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.232 2016/07/15 05:01:58 dtucker Exp $ */
+/* $OpenBSD: packet.c,v 1.233 2016/07/18 06:08:01 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1171,7 +1171,7 @@ ssh_packet_send2_wrapped(struct ssh *ssh)
 {
         struct session_state *state = ssh->state;
         u_char type, *cp, macbuf[SSH_DIGEST_MAX_LENGTH];
-        u_char padlen, pad = 0;
+        u_char tmp, padlen, pad = 0;
         u_int authlen = 0, aadlen = 0;
         u_int len;
         struct sshenc *enc   = NULL;
@@ -1229,14 +1229,24 @@ ssh_packet_send2_wrapped(struct ssh *ssh)
         if (padlen < 4)
                 padlen += block_size;
         if (state->extra_pad) {
-                /* will wrap if extra_pad+padlen > 255 */
+                tmp = state->extra_pad;
                 state->extra_pad =
                     roundup(state->extra_pad, block_size);
-                pad = state->extra_pad -
-                    ((len + padlen) % state->extra_pad);
+                /* check if roundup overflowed */
+                if (state->extra_pad < tmp)
+                        return SSH_ERR_INVALID_ARGUMENT;
+                tmp = (len + padlen) % state->extra_pad;
+                /* Check whether pad calculation below will underflow */
+                if (tmp > state->extra_pad)
+                        return SSH_ERR_INVALID_ARGUMENT;
+                pad = state->extra_pad - tmp;
                 DBG(debug3("%s: adding %d (len %d padlen %d extra_pad %d)",
                     __func__, pad, len, padlen, state->extra_pad));
+                tmp = padlen;
                 padlen += pad;
+                /* Check whether padlen calculation overflowed */
+                if (padlen < tmp)
+                        return SSH_ERR_INVALID_ARGUMENT; /* overflow */
                 state->extra_pad = 0;
         }
         if ((r = sshbuf_reserve(state->outgoing_packet, padlen, &cp)) != 0)