upstream commit

Remove support for pre-authentication compression. Doing
compression early in the protocol probably seemed reasonable in the 1990s,
but today it's clearly a bad idea in terms of both cryptography (cf. multiple
compression oracle attacks in TLS) and attack surface.

Moreover, to support it across privilege-separation zlib needed
the assistance of a complex shared-memory manager that made the
required attack surface considerably larger.

Prompted by Guido Vranken pointing out a compiler-elided security
check in the shared memory manager found by Stack
(http://css.csail.mit.edu/stack/); ok deraadt@ markus@

NB. pre-auth authentication has been disabled by default in sshd
for >10 years.

Upstream-ID: 32af9771788d45a0779693b41d06ec199d849caf

1 files changed, 6 insertions, 98 deletions

diff --git a/packet.c b/packet.c
index fb316acbc..002e8d49a 100644
--- a/packet.c
+++ b/packet.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.238 2016/09/19 19:02:19 markus Exp $ */
+/* $OpenBSD: packet.c,v 1.239 2016/09/28 16:33:07 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -756,86 +756,6 @@ uncompress_buffer(struct ssh *ssh, struct sshbuf *in, struct sshbuf *out)
         /* NOTREACHED */
 }
 
-/* Serialise compression state into a blob for privsep */
-static int
-ssh_packet_get_compress_state(struct sshbuf *m, struct ssh *ssh)
-{
-        struct session_state *state = ssh->state;
-        struct sshbuf *b;
-        int r;
-
-        if ((b = sshbuf_new()) == NULL)
-                return SSH_ERR_ALLOC_FAIL;
-        if (state->compression_in_started) {
-                if ((r = sshbuf_put_string(b, &state->compression_in_stream,
-                    sizeof(state->compression_in_stream))) != 0)
-                        goto out;
-        } else if ((r = sshbuf_put_string(b, NULL, 0)) != 0)
-                goto out;
-        if (state->compression_out_started) {
-                if ((r = sshbuf_put_string(b, &state->compression_out_stream,
-                    sizeof(state->compression_out_stream))) != 0)
-                        goto out;
-        } else if ((r = sshbuf_put_string(b, NULL, 0)) != 0)
-                goto out;
-        r = sshbuf_put_stringb(m, b);
- out:
-        sshbuf_free(b);
-        return r;
-}
-
-/* Deserialise compression state from a blob for privsep */
-static int
-ssh_packet_set_compress_state(struct ssh *ssh, struct sshbuf *m)
-{
-        struct session_state *state = ssh->state;
-        struct sshbuf *b = NULL;
-        int r;
-        const u_char *inblob, *outblob;
-        size_t inl, outl;
-
-        if ((r = sshbuf_froms(m, &b)) != 0)
-                goto out;
-        if ((r = sshbuf_get_string_direct(b, &inblob, &inl)) != 0 ||
-            (r = sshbuf_get_string_direct(b, &outblob, &outl)) != 0)
-                goto out;
-        if (inl == 0)
-                state->compression_in_started = 0;
-        else if (inl != sizeof(state->compression_in_stream)) {
-                r = SSH_ERR_INTERNAL_ERROR;
-                goto out;
-        } else {
-                state->compression_in_started = 1;
-                memcpy(&state->compression_in_stream, inblob, inl);
-        }
-        if (outl == 0)
-                state->compression_out_started = 0;
-        else if (outl != sizeof(state->compression_out_stream)) {
-                r = SSH_ERR_INTERNAL_ERROR;
-                goto out;
-        } else {
-                state->compression_out_started = 1;
-                memcpy(&state->compression_out_stream, outblob, outl);
-        }
-        r = 0;
- out:
-        sshbuf_free(b);
-        return r;
-}
-
-void
-ssh_packet_set_compress_hooks(struct ssh *ssh, void *ctx,
-    void *(*allocfunc)(void *, u_int, u_int),
-    void (*freefunc)(void *, void *))
-{
-        ssh->state->compression_out_stream.zalloc = (alloc_func)allocfunc;
-        ssh->state->compression_out_stream.zfree = (free_func)freefunc;
-        ssh->state->compression_out_stream.opaque = ctx;
-        ssh->state->compression_in_stream.zalloc = (alloc_func)allocfunc;
-        ssh->state->compression_in_stream.zfree = (free_func)freefunc;
-        ssh->state->compression_in_stream.opaque = ctx;
-}
-
 /*
  * Causes any further packets to be encrypted using the given key.  The same
  * key is used for both sending and reception.  However, both directions are
@@ -2450,21 +2370,14 @@ ssh_packet_get_output(struct ssh *ssh)
 static int
 ssh_packet_set_postauth(struct ssh *ssh)
 {
-        struct sshcomp *comp;
-        int r, mode;
+        int r;
 
         debug("%s: called", __func__);
         /* This was set in net child, but is not visible in user child */
         ssh->state->after_authentication = 1;
         ssh->state->rekeying = 0;
-        for (mode = 0; mode < MODE_MAX; mode++) {
-                if (ssh->state->newkeys[mode] == NULL)
-                        continue;
-                comp = &ssh->state->newkeys[mode]->comp;
-                if (comp && comp->enabled &&
-                    (r = ssh_packet_init_compression(ssh)) != 0)
-                        return r;
-        }
+        if ((r = ssh_packet_enable_delayed_compress(ssh)) != 0)
+                return r;
         return 0;
 }
 
@@ -2528,7 +2441,6 @@ newkeys_to_blob(struct sshbuf *m, struct ssh *ssh, int mode)
                         goto out;
         }
         if ((r = sshbuf_put_u32(b, comp->type)) != 0 ||
-            (r = sshbuf_put_u32(b, comp->enabled)) != 0 ||
             (r = sshbuf_put_cstring(b, comp->name)) != 0)
                 goto out;
         r = sshbuf_put_stringb(m, b);
@@ -2589,9 +2501,7 @@ ssh_packet_get_state(struct ssh *ssh, struct sshbuf *m)
                 return r;
         if (cipher_get_keycontext(state->receive_context, p) != (int)rlen)
                 return SSH_ERR_INTERNAL_ERROR;
-
-        if ((r = ssh_packet_get_compress_state(m, ssh)) != 0 ||
-            (r = sshbuf_put_stringb(m, state->input)) != 0 ||
+        if ((r = sshbuf_put_stringb(m, state->input)) != 0 ||
             (r = sshbuf_put_stringb(m, state->output)) != 0)
                 return r;
 
@@ -2645,7 +2555,6 @@ newkeys_from_blob(struct sshbuf *m, struct ssh *ssh, int mode)
                 mac->key_len = maclen;
         }
         if ((r = sshbuf_get_u32(b, &comp->type)) != 0 ||
-            (r = sshbuf_get_u32(b, (u_int *)&comp->enabled)) != 0 ||
             (r = sshbuf_get_cstring(b, &comp->name, NULL)) != 0)
                 goto out;
         if (enc->name == NULL ||
@@ -2773,8 +2682,7 @@ ssh_packet_set_state(struct ssh *ssh, struct sshbuf *m)
         cipher_set_keycontext(state->send_context, keyout);
         cipher_set_keycontext(state->receive_context, keyin);
 
-        if ((r = ssh_packet_set_compress_state(ssh, m)) != 0 ||
-            (r = ssh_packet_set_postauth(ssh)) != 0)
+        if ((r = ssh_packet_set_postauth(ssh)) != 0)
                 return r;
 
         sshbuf_reset(state->input);