* New upstream release (closes: #536182). Yes, I know 5.3p1 has been out

  for a while, but there's no GSSAPI patch available for it yet.
  - Change the default cipher order to prefer the AES CTR modes and the
    revised "arcfour256" mode to CBC mode ciphers that are susceptible to
    CPNI-957037 "Plaintext Recovery Attack Against SSH".
  - Add countermeasures to mitigate CPNI-957037-style attacks against the
    SSH protocol's use of CBC-mode ciphers. Upon detection of an invalid
    packet length or Message Authentication Code, ssh/sshd will continue
    reading up to the maximum supported packet length rather than
    immediately terminating the connection. This eliminates most of the
    known differences in behaviour that leaked information about the
    plaintext of injected data which formed the basis of this attack
    (closes: #506115, LP: #379329).
  - ForceCommand directive now accepts commandline arguments for the
    internal-sftp server (closes: #524423, LP: #362511).
  - Add AllowAgentForwarding to available Match keywords list (closes:
    #540623).
  - Make ssh(1) send the correct channel number for
    SSH2_MSG_CHANNEL_SUCCESS and SSH2_MSG_CHANNEL_FAILURE messages to
    avoid triggering 'Non-public channel' error messages on sshd(8) in
    openssh-5.1.
  - Avoid printing 'Non-public channel' warnings in sshd(8), since the
    ssh(1) has sent incorrect channel numbers since ~2004 (this reverts a
    behaviour introduced in openssh-5.1; closes: #496017).
* Update to GSSAPI patch from
  http://www.sxw.org.uk/computing/patches/openssh-5.2p1-gsskex-all-20090726.patch,
  including cascading credentials support (LP: #416958).

1 files changed, 65 insertions, 7 deletions

diff --git a/packet.c b/packet.c
index 3cb3decd9..5afc84ce0 100644
--- a/packet.c
+++ b/packet.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.157 2008/07/10 18:08:11 markus Exp $ */
+/* $OpenBSD: packet.c,v 1.160 2009/02/13 11:50:21 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -84,6 +84,8 @@
 #define DBG(x)
 #endif
 
+#define PACKET_MAX_SIZE (256 * 1024)
+
 /*
  * This variable contains the file descriptors used for communicating with
  * the other side.  connection_in is used for reading; connection_out for
@@ -160,6 +162,10 @@ static u_int ssh1_keylen;
 /* roundup current message to extra_pad bytes */
 static u_char extra_pad = 0;
 
+/* XXX discard incoming data after MAC error */
+static u_int packet_discard = 0;
+static Mac *packet_discard_mac = NULL;
+
 struct packet {
         TAILQ_ENTRY(packet) next;
         u_char type;
@@ -209,6 +215,36 @@ packet_set_timeout(int timeout, int count)
                 packet_timeout_ms = timeout * count * 1000;
 }
 
+static void
+packet_stop_discard(void)
+{
+        if (packet_discard_mac) {
+                char buf[1024];
+                
+                memset(buf, 'a', sizeof(buf));
+                while (buffer_len(&incoming_packet) < PACKET_MAX_SIZE)
+                        buffer_append(&incoming_packet, buf, sizeof(buf));
+                (void) mac_compute(packet_discard_mac,
+                    p_read.seqnr,
+                    buffer_ptr(&incoming_packet),
+                    PACKET_MAX_SIZE);
+        }
+        logit("Finished discarding for %.200s", get_remote_ipaddr());
+        cleanup_exit(255);
+}
+
+static void
+packet_start_discard(Enc *enc, Mac *mac, u_int packet_length, u_int discard)
+{
+        if (enc == NULL || !cipher_is_cbc(enc->cipher))
+                packet_disconnect("Packet corrupt");
+        if (packet_length != PACKET_MAX_SIZE && mac && mac->enabled)
+                packet_discard_mac = mac;
+        if (buffer_len(&input) >= discard)
+                packet_stop_discard();
+        packet_discard = discard - buffer_len(&input);
+}
+
 /* Returns 1 if remote host is connected via socket, 0 if not. */
 
 int
@@ -1127,6 +1163,9 @@ packet_read_poll2(u_int32_t *seqnr_p)
         Mac *mac   = NULL;
         Comp *comp = NULL;
 
+        if (packet_discard)
+                return SSH_MSG_NONE;
+
         if (newkeys[MODE_IN] != NULL) {
                 enc  = &newkeys[MODE_IN]->enc;
                 mac  = &newkeys[MODE_IN]->mac;
@@ -1148,12 +1187,14 @@ packet_read_poll2(u_int32_t *seqnr_p)
                     block_size);
                 cp = buffer_ptr(&incoming_packet);
                 packet_length = get_u32(cp);
-                if (packet_length < 1 + 4 || packet_length > 256 * 1024) {
+                if (packet_length < 1 + 4 || packet_length > PACKET_MAX_SIZE) {
 #ifdef PACKET_DEBUG
                         buffer_dump(&incoming_packet);
 #endif
-                        packet_disconnect("Bad packet length %-10u",
-                            packet_length);
+                        logit("Bad packet length %u.", packet_length);
+                        packet_start_discard(enc, mac, packet_length,
+                            PACKET_MAX_SIZE);
+                        return SSH_MSG_NONE;
                 }
                 DBG(debug("input: packet len %u", packet_length+4));
                 buffer_consume(&input, block_size);
@@ -1165,7 +1206,9 @@ packet_read_poll2(u_int32_t *seqnr_p)
         if (need % block_size != 0) {
                 logit("padding error: need %d block %d mod %d",
                     need, block_size, need % block_size);
-                packet_disconnect("Bad packet length %-10u", packet_length);
+                packet_start_discard(enc, mac, packet_length,
+                    PACKET_MAX_SIZE - block_size);
+                return SSH_MSG_NONE;
         }
         /*
          * check if the entire packet has been received and
@@ -1188,11 +1231,19 @@ packet_read_poll2(u_int32_t *seqnr_p)
                 macbuf = mac_compute(mac, p_read.seqnr,
                     buffer_ptr(&incoming_packet),
                     buffer_len(&incoming_packet));
-                if (memcmp(macbuf, buffer_ptr(&input), mac->mac_len) != 0)
-                        packet_disconnect("Corrupted MAC on input.");
+                if (memcmp(macbuf, buffer_ptr(&input), mac->mac_len) != 0) {
+                        logit("Corrupted MAC on input.");
+                        if (need > PACKET_MAX_SIZE)
+                                fatal("internal error need %d", need);
+                        packet_start_discard(enc, mac, packet_length,
+                            PACKET_MAX_SIZE - need);
+                        return SSH_MSG_NONE;
+                }
+                                
                 DBG(debug("MAC #%d ok", p_read.seqnr));
                 buffer_consume(&input, mac->mac_len);
         }
+        /* XXX now it's safe to use fatal/packet_disconnect */
         if (seqnr_p != NULL)
                 *seqnr_p = p_read.seqnr;
         if (++p_read.seqnr == 0)
@@ -1325,6 +1376,13 @@ packet_read_poll(void)
 void
 packet_process_incoming(const char *buf, u_int len)
 {
+        if (packet_discard) {
+                keep_alive_timeouts = 0; /* ?? */
+                if (len >= packet_discard)
+                        packet_stop_discard();
+                packet_discard -= len;
+                return;
+        }
         buffer_append(&input, buf, len);
 }