upstream: sprinkle in some explicit errors here, otherwise the

percolate all the way up to dispatch_run_fatal() and lose all meaninful
context

to help with bz#3063; ok dtucker@

OpenBSD-Commit-ID: 5b2da83bb1c4a3471444b7910b2120ae36438a0a

1 files changed, 60 insertions, 20 deletions

diff --git a/kex.c b/kex.c
index ff88dd7e3..1eb27264a 100644
--- a/kex.c
+++ b/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.151 2019/09/05 09:25:13 djm Exp $ */
+/* $OpenBSD: kex.c,v 1.152 2019/09/05 09:35:19 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -345,18 +345,25 @@ kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp)
                 r = SSH_ERR_ALLOC_FAIL;
                 goto out;
         }
-        if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) /* skip cookie */
+        if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) { /* skip cookie */
+                error("%s: consume cookie: %s", __func__, ssh_err(r));
                 goto out;
+        }
         /* extract kex init proposal strings */
         for (i = 0; i < PROPOSAL_MAX; i++) {
-                if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0)
+                if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0) {
+                        error("%s: parse proposal %u: %s", __func__,
+                            i, ssh_err(r));
                         goto out;
+                }
                 debug2("%s: %s", proposal_names[i], proposal[i]);
         }
         /* first kex follows / reserved */
         if ((r = sshbuf_get_u8(b, &v)) != 0 ||  /* first_kex_follows */
-            (r = sshbuf_get_u32(b, &i)) != 0)   /* reserved */
+            (r = sshbuf_get_u32(b, &i)) != 0) { /* reserved */
+                error("%s: parse: %s", __func__, ssh_err(r));
                 goto out;
+        }
         if (first_kex_follows != NULL)
                 *first_kex_follows = v;
         debug2("first_kex_follows %d ", v);
@@ -417,8 +424,10 @@ kex_send_ext_info(struct ssh *ssh)
             (r = sshpkt_put_u32(ssh, 1)) != 0 ||
             (r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 ||
             (r = sshpkt_put_cstring(ssh, algs)) != 0 ||
-            (r = sshpkt_send(ssh)) != 0)
+            (r = sshpkt_send(ssh)) != 0) {
+                error("%s: compose: %s", __func__, ssh_err(r));
                 goto out;
+        }
         /* success */
         r = 0;
  out:
@@ -512,23 +521,32 @@ kex_send_kexinit(struct ssh *ssh)
         struct kex *kex = ssh->kex;
         int r;
 
-        if (kex == NULL)
+        if (kex == NULL) {
+                error("%s: no hex", __func__);
                 return SSH_ERR_INTERNAL_ERROR;
+        }
         if (kex->flags & KEX_INIT_SENT)
                 return 0;
         kex->done = 0;
 
         /* generate a random cookie */
-        if (sshbuf_len(kex->my) < KEX_COOKIE_LEN)
+        if (sshbuf_len(kex->my) < KEX_COOKIE_LEN) {
+                error("%s: bad kex length: %zu < %d", __func__,
+                    sshbuf_len(kex->my), KEX_COOKIE_LEN);
                 return SSH_ERR_INVALID_FORMAT;
-        if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL)
+        }
+        if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL) {
+                error("%s: buffer error", __func__);
                 return SSH_ERR_INTERNAL_ERROR;
+        }
         arc4random_buf(cookie, KEX_COOKIE_LEN);
 
         if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0 ||
             (r = sshpkt_putb(ssh, kex->my)) != 0 ||
-            (r = sshpkt_send(ssh)) != 0)
+            (r = sshpkt_send(ssh)) != 0) {
+                error("%s: compose reply: %s", __func__, ssh_err(r));
                 return r;
+        }
         debug("SSH2_MSG_KEXINIT sent");
         kex->flags |= KEX_INIT_SENT;
         return 0;
@@ -545,21 +563,28 @@ kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh)
         int r;
 
         debug("SSH2_MSG_KEXINIT received");
-        if (kex == NULL)
-                return SSH_ERR_INVALID_ARGUMENT;
-
+        if (kex == NULL) {
+                error("%s: no hex", __func__);
+                return SSH_ERR_INTERNAL_ERROR;
+        }
         ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, NULL);
         ptr = sshpkt_ptr(ssh, &dlen);
         if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0)
                 return r;
 
         /* discard packet */
-        for (i = 0; i < KEX_COOKIE_LEN; i++)
-                if ((r = sshpkt_get_u8(ssh, NULL)) != 0)
+        for (i = 0; i < KEX_COOKIE_LEN; i++) {
+                if ((r = sshpkt_get_u8(ssh, NULL)) != 0) {
+                        error("%s: discard cookie: %s", __func__, ssh_err(r));
                         return r;
-        for (i = 0; i < PROPOSAL_MAX; i++)
-                if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0)
+                }
+        }
+        for (i = 0; i < PROPOSAL_MAX; i++) {
+                if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0) {
+                        error("%s: discard proposal: %s", __func__, ssh_err(r));
                         return r;
+                }
+        }
         /*
          * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
          * KEX method has the server move first, but a server might be using
@@ -584,6 +609,7 @@ kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh)
         if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
                 return (kex->kex[kex->kex_type])(ssh);
 
+        error("%s: unknown kex type %u", __func__, kex->kex_type);
         return SSH_ERR_INTERNAL_ERROR;
 }
 
@@ -719,6 +745,7 @@ choose_enc(struct sshenc *enc, char *client, char *server)
         if (name == NULL)
                 return SSH_ERR_NO_CIPHER_ALG_MATCH;
         if ((enc->cipher = cipher_by_name(name)) == NULL) {
+                error("%s: unsupported cipher %s", __func__, name);
                 free(name);
                 return SSH_ERR_INTERNAL_ERROR;
         }
@@ -740,6 +767,7 @@ choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server)
         if (name == NULL)
                 return SSH_ERR_NO_MAC_ALG_MATCH;
         if (mac_setup(mac, name) < 0) {
+                error("%s: unsupported MAC %s", __func__, name);
                 free(name);
                 return SSH_ERR_INTERNAL_ERROR;
         }
@@ -763,6 +791,7 @@ choose_comp(struct sshcomp *comp, char *client, char *server)
         } else if (strcmp(name, "none") == 0) {
                 comp->type = COMP_NONE;
         } else {
+                error("%s: unsupported compression scheme %s", __func__, name);
                 free(name);
                 return SSH_ERR_INTERNAL_ERROR;
         }
@@ -780,8 +809,10 @@ choose_kex(struct kex *k, char *client, char *server)
         debug("kex: algorithm: %s", k->name ? k->name : "(no match)");
         if (k->name == NULL)
                 return SSH_ERR_NO_KEX_ALG_MATCH;
-        if ((kexalg = kex_alg_by_name(k->name)) == NULL)
+        if ((kexalg = kex_alg_by_name(k->name)) == NULL) {
+                error("%s: unsupported KEX method %s", __func__, k->name);
                 return SSH_ERR_INTERNAL_ERROR;
+        }
         k->kex_type = kexalg->type;
         k->hash_alg = kexalg->hash_alg;
         k->ec_nid = kexalg->ec_nid;
@@ -798,8 +829,11 @@ choose_hostkeyalg(struct kex *k, char *client, char *server)
         if (k->hostkey_alg == NULL)
                 return SSH_ERR_NO_HOSTKEY_ALG_MATCH;
         k->hostkey_type = sshkey_type_from_name(k->hostkey_alg);
-        if (k->hostkey_type == KEY_UNSPEC)
+        if (k->hostkey_type == KEY_UNSPEC) {
+                error("%s: unsupported hostkey algorithm %s", __func__,
+                    k->hostkey_alg);
                 return SSH_ERR_INTERNAL_ERROR;
+        }
         k->hostkey_nid = sshkey_ecdsa_nid_from_name(k->hostkey_alg);
         return 0;
 }
@@ -968,6 +1002,7 @@ derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen,
             kex->session_id_len) != 0 ||
             ssh_digest_final(hashctx, digest, mdsz) != 0) {
                 r = SSH_ERR_LIBCRYPTO_ERROR;
+                error("%s: KEX hash failed", __func__);
                 goto out;
         }
         ssh_digest_free(hashctx);
@@ -984,6 +1019,7 @@ derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen,
                     ssh_digest_update(hashctx, hash, hashlen) != 0 ||
                     ssh_digest_update(hashctx, digest, have) != 0 ||
                     ssh_digest_final(hashctx, digest + have, mdsz) != 0) {
+                        error("%s: KDF failed", __func__);
                         r = SSH_ERR_LIBCRYPTO_ERROR;
                         goto out;
                 }
@@ -1047,8 +1083,10 @@ kex_load_hostkey(struct ssh *ssh, struct sshkey **prvp, struct sshkey **pubp)
         *pubp = NULL;
         *prvp = NULL;
         if (kex->load_host_public_key == NULL ||
-            kex->load_host_private_key == NULL)
+            kex->load_host_private_key == NULL) {
+                error("%s: missing hostkey loader", __func__);
                 return SSH_ERR_INVALID_ARGUMENT;
+        }
         *pubp = kex->load_host_public_key(kex->hostkey_type,
             kex->hostkey_nid, ssh);
         *prvp = kex->load_host_private_key(kex->hostkey_type,
@@ -1063,8 +1101,10 @@ kex_verify_host_key(struct ssh *ssh, struct sshkey *server_host_key)
 {
         struct kex *kex = ssh->kex;
 
-        if (kex->verify_host_key == NULL)
+        if (kex->verify_host_key == NULL) {
+                error("%s: missing hostkey verifier", __func__);
                 return SSH_ERR_INVALID_ARGUMENT;
+        }
         if (server_host_key->type != kex->hostkey_type ||
             (kex->hostkey_type == KEY_ECDSA &&
             server_host_key->ecdsa_nid != kex->hostkey_nid))