upstream commit

adapt kex to sshbuf and struct ssh; ok djm@

1 files changed, 338 insertions, 237 deletions

diff --git a/kex.c b/kex.c
index 92ebaf732..9280dd3f4 100644
--- a/kex.c
+++ b/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.101 2015/01/19 20:07:45 markus Exp $ */
+/* $OpenBSD: kex.c,v 1.102 2015/01/19 20:16:15 markus Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -37,20 +37,22 @@
 #include <openssl/crypto.h>
 #endif
 
-#include "xmalloc.h"
 #include "ssh2.h"
-#include "buffer.h"
 #include "packet.h"
 #include "compat.h"
 #include "cipher.h"
-#include "key.h"
+#include "sshkey.h"
 #include "kex.h"
 #include "log.h"
 #include "mac.h"
 #include "match.h"
+#include "misc.h"
 #include "dispatch.h"
 #include "monitor.h"
 #include "roaming.h"
+
+#include "ssherr.h"
+#include "sshbuf.h"
 #include "digest.h"
 
 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
@@ -62,12 +64,12 @@ extern const EVP_MD *evp_ssh_sha256(void);
 #endif
 
 /* prototype */
-static void kex_kexinit_finish(Kex *);
-static void kex_choose_conf(Kex *);
+static int kex_choose_conf(struct ssh *);
+static int kex_input_newkeys(int, u_int32_t, void *);
 
 struct kexalg {
         char *name;
-        int type;
+        u_int type;
         int ec_nid;
         int hash_alg;
 };
@@ -99,7 +101,7 @@ static const struct kexalg kexalgs[] = {
 char *
 kex_alg_list(char sep)
 {
-        char *ret = NULL;
+        char *ret = NULL, *tmp;
         size_t nlen, rlen = 0;
         const struct kexalg *k;
 
@@ -107,7 +109,11 @@ kex_alg_list(char sep)
                 if (ret != NULL)
                         ret[rlen++] = sep;
                 nlen = strlen(k->name);
-                ret = xrealloc(ret, 1, rlen + nlen + 2);
+                if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
+                        free(ret);
+                        return NULL;
+                }
+                ret = tmp;
                 memcpy(ret + rlen, k->name, nlen + 1);
                 rlen += nlen;
         }
@@ -134,7 +140,8 @@ kex_names_valid(const char *names)
 
         if (names == NULL || strcmp(names, "") == 0)
                 return 0;
-        s = cp = xstrdup(names);
+        if ((s = cp = strdup(names)) == NULL)
+                return 0;
         for ((p = strsep(&cp, ",")); p && *p != '\0';
             (p = strsep(&cp, ","))) {
                 if (kex_alg_by_name(p) == NULL) {
@@ -149,56 +156,75 @@ kex_names_valid(const char *names)
 }
 
 /* put algorithm proposal into buffer */
-static void
-kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
+int
+kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX])
 {
         u_int i;
+        int r;
+
+        sshbuf_reset(b);
 
-        buffer_clear(b);
         /*
          * add a dummy cookie, the cookie will be overwritten by
          * kex_send_kexinit(), each time a kexinit is set
          */
-        for (i = 0; i < KEX_COOKIE_LEN; i++)
-                buffer_put_char(b, 0);
-        for (i = 0; i < PROPOSAL_MAX; i++)
-                buffer_put_cstring(b, proposal[i]);
-        buffer_put_char(b, 0);                  /* first_kex_packet_follows */
-        buffer_put_int(b, 0);                   /* uint32 reserved */
+        for (i = 0; i < KEX_COOKIE_LEN; i++) {
+                if ((r = sshbuf_put_u8(b, 0)) != 0)
+                        return r;
+        }
+        for (i = 0; i < PROPOSAL_MAX; i++) {
+                if ((r = sshbuf_put_cstring(b, proposal[i])) != 0)
+                        return r;
+        }
+        if ((r = sshbuf_put_u8(b, 0)) != 0 ||   /* first_kex_packet_follows */
+            (r = sshbuf_put_u32(b, 0)) != 0)    /* uint32 reserved */
+                return r;
+        return 0;
 }
 
 /* parse buffer and return algorithm proposal */
-static char **
-kex_buf2prop(Buffer *raw, int *first_kex_follows)
+int
+kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp)
 {
-        Buffer b;
+        struct sshbuf *b = NULL;
+        u_char v;
         u_int i;
-        char **proposal;
-
-        proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
-
-        buffer_init(&b);
-        buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
-        /* skip cookie */
-        for (i = 0; i < KEX_COOKIE_LEN; i++)
-                buffer_get_char(&b);
+        char **proposal = NULL;
+        int r;
+
+        *propp = NULL;
+        if ((proposal = calloc(PROPOSAL_MAX, sizeof(char *))) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
+        if ((b = sshbuf_fromb(raw)) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) /* skip cookie */
+                goto out;
         /* extract kex init proposal strings */
         for (i = 0; i < PROPOSAL_MAX; i++) {
-                proposal[i] = buffer_get_cstring(&b,NULL);
+                if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0)
+                        goto out;
                 debug2("kex_parse_kexinit: %s", proposal[i]);
         }
         /* first kex follows / reserved */
-        i = buffer_get_char(&b);
+        if ((r = sshbuf_get_u8(b, &v)) != 0 ||
+            (r = sshbuf_get_u32(b, &i)) != 0)
+                goto out;
         if (first_kex_follows != NULL)
                 *first_kex_follows = i;
-        debug2("kex_parse_kexinit: first_kex_follows %d ", i);
-        i = buffer_get_int(&b);
+        debug2("kex_parse_kexinit: first_kex_follows %d ", v);
         debug2("kex_parse_kexinit: reserved %u ", i);
-        buffer_free(&b);
-        return proposal;
+        r = 0;
+        *propp = proposal;
+ out:
+        if (r != 0 && proposal != NULL)
+                kex_prop_free(proposal);
+        sshbuf_free(b);
+        return r;
 }
 
-static void
+void
 kex_prop_free(char **proposal)
 {
         u_int i;
@@ -217,91 +243,103 @@ kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 }
 
 static void
-kex_reset_dispatch(void)
+kex_reset_dispatch(struct ssh *ssh)
 {
-        dispatch_range(SSH2_MSG_TRANSPORT_MIN,
+        ssh_dispatch_range(ssh, SSH2_MSG_TRANSPORT_MIN,
             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
-        dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
+        ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
 }
 
-void
-kex_finish(Kex *kex)
+int
+kex_send_newkeys(struct ssh *ssh)
 {
-        kex_reset_dispatch();
+        int r;
 
-        packet_start(SSH2_MSG_NEWKEYS);
-        packet_send();
-        /* packet_write_wait(); */
+        kex_reset_dispatch(ssh);
+        if ((r = sshpkt_start(ssh, SSH2_MSG_NEWKEYS)) != 0 ||
+            (r = sshpkt_send(ssh)) != 0)
+                return r;
         debug("SSH2_MSG_NEWKEYS sent");
-
         debug("expecting SSH2_MSG_NEWKEYS");
-        packet_read_expect(SSH2_MSG_NEWKEYS);
-        packet_check_eom();
-        debug("SSH2_MSG_NEWKEYS received");
+        ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_input_newkeys);
+        return 0;
+}
+
+static int
+kex_input_newkeys(int type, u_int32_t seq, void *ctxt)
+{
+        struct ssh *ssh = ctxt;
+        struct kex *kex = ssh->kex;
+        int r;
 
+        debug("SSH2_MSG_NEWKEYS received");
+        ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_protocol_error);
+        if ((r = sshpkt_get_end(ssh)) != 0)
+                return r;
         kex->done = 1;
-        buffer_clear(kex->peer);
-        /* buffer_clear(kex->my); */
+        sshbuf_reset(kex->peer);
+        /* sshbuf_reset(kex->my); */
         kex->flags &= ~KEX_INIT_SENT;
         free(kex->name);
         kex->name = NULL;
+        return 0;
 }
 
-void
-kex_send_kexinit(Kex *kex)
+int
+kex_send_kexinit(struct ssh *ssh)
 {
-        u_int32_t rnd = 0;
         u_char *cookie;
-        u_int i;
+        struct kex *kex = ssh->kex;
+        int r;
 
-        if (kex == NULL) {
-                error("kex_send_kexinit: no kex, cannot rekey");
-                return;
-        }
-        if (kex->flags & KEX_INIT_SENT) {
-                debug("KEX_INIT_SENT");
-                return;
-        }
+        if (kex == NULL)
+                return SSH_ERR_INTERNAL_ERROR;
+        if (kex->flags & KEX_INIT_SENT)
+                return 0;
         kex->done = 0;
 
         /* generate a random cookie */
-        if (buffer_len(kex->my) < KEX_COOKIE_LEN)
-                fatal("kex_send_kexinit: kex proposal too short");
-        cookie = buffer_ptr(kex->my);
-        for (i = 0; i < KEX_COOKIE_LEN; i++) {
-                if (i % 4 == 0)
-                        rnd = arc4random();
-                cookie[i] = rnd;
-                rnd >>= 8;
-        }
-        packet_start(SSH2_MSG_KEXINIT);
-        packet_put_raw(buffer_ptr(kex->my), buffer_len(kex->my));
-        packet_send();
+        if (sshbuf_len(kex->my) < KEX_COOKIE_LEN)
+                return SSH_ERR_INVALID_FORMAT;
+        if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL)
+                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)
+                return r;
         debug("SSH2_MSG_KEXINIT sent");
         kex->flags |= KEX_INIT_SENT;
+        return 0;
 }
 
 /* ARGSUSED */
 int
 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 {
-        const char *ptr;
+        struct ssh *ssh = ctxt;
+        struct kex *kex = ssh->kex;
+        const u_char *ptr;
         u_int i;
         size_t dlen;
-        Kex *kex = (Kex *)ctxt;
+        int r;
 
         debug("SSH2_MSG_KEXINIT received");
         if (kex == NULL)
-                fatal("kex_input_kexinit: no kex, cannot rekey");
+                return SSH_ERR_INVALID_ARGUMENT;
 
-        ptr = packet_get_raw(&dlen);
-        buffer_append(kex->peer, ptr, dlen);
+        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++)
-                packet_get_char();
+                if ((r = sshpkt_get_u8(ssh, NULL)) != 0)
+                        return r;
         for (i = 0; i < PROPOSAL_MAX; i++)
-                free(packet_get_string(NULL));
+                if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0)
+                        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
@@ -312,12 +350,47 @@ kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
          * for cases where the server *doesn't* go first. I guess we should
          * ignore it when it is set for these cases, which is what we do now.
          */
-        (void) packet_get_char();       /* first_kex_follows */
-        (void) packet_get_int();        /* reserved */
-        packet_check_eom();
+        if ((r = sshpkt_get_u8(ssh, NULL)) != 0 ||      /* first_kex_follows */
+            (r = sshpkt_get_u32(ssh, NULL)) != 0 ||     /* reserved */
+            (r = sshpkt_get_end(ssh)) != 0)
+                        return r;
 
-        kex_kexinit_finish(kex);
-        return 0;
+        if (!(kex->flags & KEX_INIT_SENT))
+                if ((r = kex_send_kexinit(ssh)) != 0)
+                        return r;
+        if ((r = kex_choose_conf(ssh)) != 0)
+                return r;
+
+        if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
+                return (kex->kex[kex->kex_type])(ssh);
+
+        return SSH_ERR_INTERNAL_ERROR;
+}
+
+int
+kex_new(struct ssh *ssh, char *proposal[PROPOSAL_MAX], struct kex **kexp)
+{
+        struct kex *kex;
+        int r;
+
+        *kexp = NULL;
+        if ((kex = calloc(1, sizeof(*kex))) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
+        if ((kex->peer = sshbuf_new()) == NULL ||
+            (kex->my = sshbuf_new()) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = kex_prop2buf(kex->my, proposal)) != 0)
+                goto out;
+        kex->done = 0;
+        kex_reset_dispatch(ssh);
+        r = 0;
+        *kexp = kex;
+ out:
+        if (r != 0)
+                kex_free(kex);
+        return r;
 }
 
 void
@@ -351,51 +424,53 @@ kex_free_newkeys(struct newkeys *newkeys)
         free(newkeys);
 }
 
-Kex *
-kex_setup(char *proposal[PROPOSAL_MAX])
+void
+kex_free(struct kex *kex)
 {
-        struct kex *kex;
+        u_int mode;
 
-        if ((kex = calloc(1, sizeof(*kex))) == NULL)
-                fatal("%s: calloc", __func__);
-        if ((kex->peer = sshbuf_new()) == NULL ||
-            (kex->my = sshbuf_new()) == NULL) {
-                fatal("%s: sshbuf_new", __func__);
+#ifdef WITH_OPENSSL
+        if (kex->dh)
+                DH_free(kex->dh);
+        if (kex->ec_client_key)
+                EC_KEY_free(kex->ec_client_key);
+#endif
+        for (mode = 0; mode < MODE_MAX; mode++) {
+                kex_free_newkeys(kex->newkeys[mode]);
+                kex->newkeys[mode] = NULL;
         }
-        kex_prop2buf(kex->my, proposal);
-        kex->done = 0;
-
-        kex_send_kexinit(kex);                                  /* we start */
-        kex_reset_dispatch();
-
-        return kex;
+        sshbuf_free(kex->peer);
+        sshbuf_free(kex->my);
+        free(kex->session_id);
+        free(kex->client_version_string);
+        free(kex->server_version_string);
+        free(kex);
 }
 
-static void
-kex_kexinit_finish(Kex *kex)
+int
+kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
 {
-        if (!(kex->flags & KEX_INIT_SENT))
-                kex_send_kexinit(kex);
-
-        kex_choose_conf(kex);
-
-        if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
-            kex->kex[kex->kex_type] != NULL) {
-                (kex->kex[kex->kex_type])(kex);
-        } else {
-                fatal("Unsupported key exchange %d", kex->kex_type);
+        int r;
+
+        if ((r = kex_new(ssh, proposal, &ssh->kex)) != 0)
+                return r;
+        if ((r = kex_send_kexinit(ssh)) != 0) {         /* we start */
+                kex_free(ssh->kex);
+                ssh->kex = NULL;
+                return r;
         }
+        return 0;
 }
 
-static void
-choose_enc(Enc *enc, char *client, char *server)
+static int
+choose_enc(struct sshenc *enc, char *client, char *server)
 {
         char *name = match_list(client, server, NULL);
+
         if (name == NULL)
-                fatal("no matching cipher found: client %s server %s",
-                    client, server);
+                return SSH_ERR_NO_CIPHER_ALG_MATCH;
         if ((enc->cipher = cipher_by_name(name)) == NULL)
-                fatal("matching cipher is not supported: %s", name);
+                return SSH_ERR_INTERNAL_ERROR;
         enc->name = name;
         enc->enabled = 0;
         enc->iv = NULL;
@@ -403,31 +478,34 @@ choose_enc(Enc *enc, char *client, char *server)
         enc->key = NULL;
         enc->key_len = cipher_keylen(enc->cipher);
         enc->block_size = cipher_blocksize(enc->cipher);
+        return 0;
 }
 
-static void
-choose_mac(Mac *mac, char *client, char *server)
+static int
+choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server)
 {
         char *name = match_list(client, server, NULL);
+
         if (name == NULL)
-                fatal("no matching mac found: client %s server %s",
-                    client, server);
+                return SSH_ERR_NO_MAC_ALG_MATCH;
         if (mac_setup(mac, name) < 0)
-                fatal("unsupported mac %s", name);
+                return SSH_ERR_INTERNAL_ERROR;
         /* truncate the key */
-        if (datafellows & SSH_BUG_HMAC)
+        if (ssh->compat & SSH_BUG_HMAC)
                 mac->key_len = 16;
         mac->name = name;
         mac->key = NULL;
         mac->enabled = 0;
+        return 0;
 }
 
-static void
-choose_comp(Comp *comp, char *client, char *server)
+static int
+choose_comp(struct sshcomp *comp, char *client, char *server)
 {
         char *name = match_list(client, server, NULL);
+
         if (name == NULL)
-                fatal("no matching comp found: client %s server %s", client, server);
+                return SSH_ERR_NO_COMPRESS_ALG_MATCH;
         if (strcmp(name, "zlib@openssh.com") == 0) {
                 comp->type = COMP_DELAYED;
         } else if (strcmp(name, "zlib") == 0) {
@@ -435,36 +513,41 @@ choose_comp(Comp *comp, char *client, char *server)
         } else if (strcmp(name, "none") == 0) {
                 comp->type = COMP_NONE;
         } else {
-                fatal("unsupported comp %s", name);
+                return SSH_ERR_INTERNAL_ERROR;
         }
         comp->name = name;
+        return 0;
 }
 
-static void
-choose_kex(Kex *k, char *client, char *server)
+static int
+choose_kex(struct kex *k, char *client, char *server)
 {
         const struct kexalg *kexalg;
 
         k->name = match_list(client, server, NULL);
+
         if (k->name == NULL)
-                fatal("Unable to negotiate a key exchange method");
+                return SSH_ERR_NO_KEX_ALG_MATCH;
         if ((kexalg = kex_alg_by_name(k->name)) == NULL)
-                fatal("unsupported kex alg %s", k->name);
+                return SSH_ERR_INTERNAL_ERROR;
         k->kex_type = kexalg->type;
         k->hash_alg = kexalg->hash_alg;
         k->ec_nid = kexalg->ec_nid;
+        return 0;
 }
 
-static void
-choose_hostkeyalg(Kex *k, char *client, char *server)
+static int
+choose_hostkeyalg(struct kex *k, char *client, char *server)
 {
         char *hostkeyalg = match_list(client, server, NULL);
+
         if (hostkeyalg == NULL)
-                fatal("no hostkey alg");
-        k->hostkey_type = key_type_from_name(hostkeyalg);
+                return SSH_ERR_NO_HOSTKEY_ALG_MATCH;
+        k->hostkey_type = sshkey_type_from_name(hostkeyalg);
         if (k->hostkey_type == KEY_UNSPEC)
-                fatal("bad hostkey alg '%s'", hostkeyalg);
+                return SSH_ERR_INTERNAL_ERROR;
         free(hostkeyalg);
+        return 0;
 }
 
 static int
@@ -491,18 +574,20 @@ proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
         return (1);
 }
 
-static void
-kex_choose_conf(Kex *kex)
+static int
+kex_choose_conf(struct ssh *ssh)
 {
-        Newkeys *newkeys;
-        char **my, **peer;
+        struct kex *kex = ssh->kex;
+        struct newkeys *newkeys;
+        char **my = NULL, **peer = NULL;
         char **cprop, **sprop;
         int nenc, nmac, ncomp;
         u_int mode, ctos, need, dh_need, authlen;
-        int first_kex_follows, type;
+        int r, first_kex_follows;
 
-        my   = kex_buf2prop(kex->my, NULL);
-        peer = kex_buf2prop(kex->peer, &first_kex_follows);
+        if ((r = kex_buf2prop(kex->my, NULL, &my)) != 0 ||
+            (r = kex_buf2prop(kex->peer, &first_kex_follows, &peer)) != 0)
+                goto out;
 
         if (kex->server) {
                 cprop=peer;
@@ -514,8 +599,9 @@ kex_choose_conf(Kex *kex)
 
         /* Check whether server offers roaming */
         if (!kex->server) {
-                char *roaming;
-                roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
+                char *roaming = match_list(KEX_RESUME,
+                    peer[PROPOSAL_KEX_ALGS], NULL);
+
                 if (roaming) {
                         kex->roaming = 1;
                         free(roaming);
@@ -524,28 +610,39 @@ kex_choose_conf(Kex *kex)
 
         /* Algorithm Negotiation */
         for (mode = 0; mode < MODE_MAX; mode++) {
-                newkeys = xcalloc(1, sizeof(*newkeys));
+                if ((newkeys = calloc(1, sizeof(*newkeys))) == NULL) {
+                        r = SSH_ERR_ALLOC_FAIL;
+                        goto out;
+                }
                 kex->newkeys[mode] = newkeys;
                 ctos = (!kex->server && mode == MODE_OUT) ||
                     (kex->server && mode == MODE_IN);
                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
-                choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]);
-                /* ignore mac for authenticated encryption */
+                if ((r = choose_enc(&newkeys->enc, cprop[nenc],
+                    sprop[nenc])) != 0)
+                        goto out;
                 authlen = cipher_authlen(newkeys->enc.cipher);
-                if (authlen == 0)
-                        choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]);
-                choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
+                /* ignore mac for authenticated encryption */
+                if (authlen == 0 &&
+                    (r = choose_mac(ssh, &newkeys->mac, cprop[nmac],
+                    sprop[nmac])) != 0)
+                        goto out;
+                if ((r = choose_comp(&newkeys->comp, cprop[ncomp],
+                    sprop[ncomp])) != 0)
+                        goto out;
                 debug("kex: %s %s %s %s",
                     ctos ? "client->server" : "server->client",
                     newkeys->enc.name,
                     authlen == 0 ? newkeys->mac.name : "<implicit>",
                     newkeys->comp.name);
         }
-        choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
-        choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
-            sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
+        if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS],
+            sprop[PROPOSAL_KEX_ALGS])) != 0 ||
+            (r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
+            sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0)
+                goto out;
         need = dh_need = 0;
         for (mode = 0; mode < MODE_MAX; mode++) {
                 newkeys = kex->newkeys[mode];
@@ -564,45 +661,47 @@ kex_choose_conf(Kex *kex)
 
         /* ignore the next message if the proposals do not match */
         if (first_kex_follows && !proposals_match(my, peer) &&
-            !(datafellows & SSH_BUG_FIRSTKEX)) {
-                type = packet_read();
-                debug2("skipping next packet (type %u)", type);
-        }
-
+            !(ssh->compat & SSH_BUG_FIRSTKEX))
+                ssh->dispatch_skip_packets = 1;
+        r = 0;
+ out:
         kex_prop_free(my);
         kex_prop_free(peer);
+        return r;
 }
 
-static u_char *
-derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
-    const u_char *shared_secret, u_int slen)
+static int
+derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen,
+    const struct sshbuf *shared_secret, u_char **keyp)
 {
-        Buffer b;
-        struct ssh_digest_ctx *hashctx;
+        struct kex *kex = ssh->kex;
+        struct ssh_digest_ctx *hashctx = NULL;
         char c = id;
         u_int have;
         size_t mdsz;
         u_char *digest;
+        int r;
 
         if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
-                fatal("bad kex md size %zu", mdsz);
-        digest = xmalloc(roundup(need, mdsz));
-
-        buffer_init(&b);
-        buffer_append(&b, shared_secret, slen);
+                return SSH_ERR_INVALID_ARGUMENT;
+        if ((digest = calloc(1, roundup(need, mdsz))) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
 
         /* K1 = HASH(K || H || "A" || session_id) */
-        if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
-                fatal("%s: ssh_digest_start failed", __func__);
-        if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
+        if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
+            ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
             ssh_digest_update(hashctx, hash, hashlen) != 0 ||
             ssh_digest_update(hashctx, &c, 1) != 0 ||
             ssh_digest_update(hashctx, kex->session_id,
-            kex->session_id_len) != 0)
-                fatal("%s: ssh_digest_update failed", __func__);
-        if (ssh_digest_final(hashctx, digest, mdsz) != 0)
-                fatal("%s: ssh_digest_final failed", __func__);
+            kex->session_id_len) != 0 ||
+            ssh_digest_final(hashctx, digest, mdsz) != 0) {
+                r = SSH_ERR_LIBCRYPTO_ERROR;
+                goto out;
+        }
         ssh_digest_free(hashctx);
+        hashctx = NULL;
 
         /*
          * expand key:
@@ -610,38 +709,49 @@ derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
          * Key = K1 || K2 || ... || Kn
          */
         for (have = mdsz; need > have; have += mdsz) {
-                if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
-                        fatal("%s: ssh_digest_start failed", __func__);
-                if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
+                if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
+                    ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
                     ssh_digest_update(hashctx, hash, hashlen) != 0 ||
-                    ssh_digest_update(hashctx, digest, have) != 0)
-                        fatal("%s: ssh_digest_update failed", __func__);
-                if (ssh_digest_final(hashctx, digest + have, mdsz) != 0)
-                        fatal("%s: ssh_digest_final failed", __func__);
+                    ssh_digest_update(hashctx, digest, have) != 0 ||
+                    ssh_digest_final(hashctx, digest + have, mdsz) != 0) {
+                        r = SSH_ERR_LIBCRYPTO_ERROR;
+                        goto out;
+                }
                 ssh_digest_free(hashctx);
+                hashctx = NULL;
         }
-        buffer_free(&b);
 #ifdef DEBUG_KEX
         fprintf(stderr, "key '%c'== ", c);
         dump_digest("key", digest, need);
 #endif
-        return digest;
+        *keyp = digest;
+        digest = NULL;
+        r = 0;
+ out:
+        if (digest)
+                free(digest);
+        ssh_digest_free(hashctx);
+        return r;
 }
 
 #define NKEYS   6
-void
-kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen,
-    const u_char *shared_secret, u_int slen)
+int
+kex_derive_keys(struct ssh *ssh, u_char *hash, u_int hashlen,
+    const struct sshbuf *shared_secret)
 {
+        struct kex *kex = ssh->kex;
         u_char *keys[NKEYS];
-        u_int i, mode, ctos;
+        u_int i, j, mode, ctos;
+        int r;
 
         for (i = 0; i < NKEYS; i++) {
-                keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
-                    shared_secret, slen);
+                if ((r = derive_key(ssh, 'A'+i, kex->we_need, hash, hashlen,
+                    shared_secret, &keys[i])) != 0) {
+                        for (j = 0; j < i; j++)
+                                free(keys[j]);
+                        return r;
+                }
         }
-
-        debug2("kex_derive_keys");
         for (mode = 0; mode < MODE_MAX; mode++) {
                 ctos = (!kex->server && mode == MODE_OUT) ||
                     (kex->server && mode == MODE_IN);
@@ -649,54 +759,54 @@ kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen,
                 kex->newkeys[mode]->enc.key = keys[ctos ? 2 : 3];
                 kex->newkeys[mode]->mac.key = keys[ctos ? 4 : 5];
         }
+        return 0;
 }
 
 #ifdef WITH_OPENSSL
-void
-kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret)
+int
+kex_derive_keys_bn(struct ssh *ssh, u_char *hash, u_int hashlen,
+    const BIGNUM *secret)
 {
-        Buffer shared_secret;
-
-        buffer_init(&shared_secret);
-        buffer_put_bignum2(&shared_secret, secret);
-        kex_derive_keys(kex, hash, hashlen,
-            buffer_ptr(&shared_secret), buffer_len(&shared_secret));
-        buffer_free(&shared_secret);
+        struct sshbuf *shared_secret;
+        int r;
+
+        if ((shared_secret = sshbuf_new()) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
+        if ((r = sshbuf_put_bignum2(shared_secret, secret)) == 0)
+                r = kex_derive_keys(ssh, hash, hashlen, shared_secret);
+        sshbuf_free(shared_secret);
+        return r;
 }
 #endif
 
 #ifdef WITH_SSH1
-void
+int
 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
     u_int8_t cookie[8], u_int8_t id[16])
 {
         u_int8_t nbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH];
-        int len;
-        struct ssh_digest_ctx *hashctx;
-
-        if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL)
-                fatal("%s: ssh_digest_start", __func__);
+        struct ssh_digest_ctx *hashctx = NULL;
+        size_t len;
+        int r;
 
         len = BN_num_bytes(host_modulus);
         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
-                fatal("%s: bad host modulus (len %d)", __func__, len);
-        BN_bn2bin(host_modulus, nbuf);
-        if (ssh_digest_update(hashctx, nbuf, len) != 0)
-                fatal("%s: ssh_digest_update failed", __func__);
-
-        len = BN_num_bytes(server_modulus);
-        if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
-                fatal("%s: bad server modulus (len %d)", __func__, len);
-        BN_bn2bin(server_modulus, nbuf);
-        if (ssh_digest_update(hashctx, nbuf, len) != 0 ||
-            ssh_digest_update(hashctx, cookie, 8) != 0)
-                fatal("%s: ssh_digest_update failed", __func__);
-        if (ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0)
-                fatal("%s: ssh_digest_final failed", __func__);
+                return SSH_ERR_KEY_BITS_MISMATCH;
+        if (BN_bn2bin(host_modulus, nbuf) <= 0 ||
+            (hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL ||
+            ssh_digest_update(hashctx, nbuf, len) != 0 ||
+            ssh_digest_update(hashctx, cookie, 8) != 0 ||
+            ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0) {
+                r = SSH_ERR_LIBCRYPTO_ERROR;
+                goto out;
+        }
         memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5));
-
+        r = 0;
+ out:
+        ssh_digest_free(hashctx);
         explicit_bzero(nbuf, sizeof(nbuf));
         explicit_bzero(obuf, sizeof(obuf));
+        return r;
 }
 #endif
 
@@ -704,16 +814,7 @@ derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 void
 dump_digest(char *msg, u_char *digest, int len)
 {
-        int i;
-
         fprintf(stderr, "%s\n", msg);
-        for (i = 0; i < len; i++) {
-                fprintf(stderr, "%02x", digest[i]);
-                if (i%32 == 31)
-                        fprintf(stderr, "\n");
-                else if (i%8 == 7)
-                        fprintf(stderr, " ");
-        }
-        fprintf(stderr, "\n");
+        sshbuf_dump_data(digest, len, stderr);
 }
 #endif