From 779974d35b4859c07bc3cb8a12c74b43b0a7d1e0 Mon Sep 17 00:00:00 2001
From: djm <djm@openbsd.org>
Date: Tue, 31 Jul 2018 03:10:27 +0000
Subject: [PATCH] =?utf8?q?delay=20bailout=20for=20invalid=20authenticating?=
 =?utf8?q?=20user=20until=20after=20the=20packet=20containing=20the=20requ?=
 =?utf8?q?est=20has=20been=20fully=20parsed.=20Reported=20by=20Dariusz=20T?=
 =?utf8?q?ytko=20and=20Micha=C5=82=20Sajdak;=20ok=20deraadt?=
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

---
 usr.bin/ssh/auth2-gss.c       | 11 +++++++----
 usr.bin/ssh/auth2-hostbased.c | 11 ++++++-----
 usr.bin/ssh/auth2-pubkey.c    | 25 +++++++++++++++----------
 3 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/usr.bin/ssh/auth2-gss.c b/usr.bin/ssh/auth2-gss.c
index 649c830916a..c919ef4c353 100644
--- a/usr.bin/ssh/auth2-gss.c
+++ b/usr.bin/ssh/auth2-gss.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-gss.c,v 1.28 2018/07/10 09:13:30 djm Exp $ */
+/* $OpenBSD: auth2-gss.c,v 1.29 2018/07/31 03:10:27 djm Exp $ */
 
 /*
  * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
@@ -65,9 +65,6 @@ userauth_gssapi(struct ssh *ssh)
 	size_t len;
 	u_char *doid = NULL;
 
-	if (!authctxt->valid || authctxt->user == NULL)
-		return (0);
-
 	if ((r = sshpkt_get_u32(ssh, &mechs)) != 0)
 		fatal("%s: %s", __func__, ssh_err(r));
 
@@ -101,6 +98,12 @@ userauth_gssapi(struct ssh *ssh)
 		return (0);
 	}
 
+	if (!authctxt->valid || authctxt->user == NULL) {
+		debug2("%s: disabled because of invalid user", __func__);
+		free(doid);
+		return (0);
+	}
+
 	if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, &goid)))) {
 		if (ctxt != NULL)
 			ssh_gssapi_delete_ctx(&ctxt);
diff --git a/usr.bin/ssh/auth2-hostbased.c b/usr.bin/ssh/auth2-hostbased.c
index ad335555934..fb5e5f42272 100644
--- a/usr.bin/ssh/auth2-hostbased.c
+++ b/usr.bin/ssh/auth2-hostbased.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-hostbased.c,v 1.35 2018/07/09 21:35:50 markus Exp $ */
+/* $OpenBSD: auth2-hostbased.c,v 1.36 2018/07/31 03:10:27 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -66,10 +66,6 @@ userauth_hostbased(struct ssh *ssh)
 	size_t alen, blen, slen;
 	int r, pktype, authenticated = 0;
 
-	if (!authctxt->valid) {
-		debug2("%s: disabled because of invalid user", __func__);
-		return 0;
-	}
 	/* XXX use sshkey_froms() */
 	if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
 	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
@@ -116,6 +112,11 @@ userauth_hostbased(struct ssh *ssh)
 		goto done;
 	}
 
+	if (!authctxt->valid || authctxt->user == NULL) {
+		debug2("%s: disabled because of invalid user", __func__);
+		goto done;
+	}
+
 	if ((b = sshbuf_new()) == NULL)
 		fatal("%s: sshbuf_new failed", __func__);
 	/* reconstruct packet */
diff --git a/usr.bin/ssh/auth2-pubkey.c b/usr.bin/ssh/auth2-pubkey.c
index 195da5e2111..af9e5f04c45 100644
--- a/usr.bin/ssh/auth2-pubkey.c
+++ b/usr.bin/ssh/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.82 2018/07/11 18:55:11 markus Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.83 2018/07/31 03:10:27 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -86,19 +86,15 @@ userauth_pubkey(struct ssh *ssh)
 {
 	Authctxt *authctxt = ssh->authctxt;
 	struct passwd *pw = authctxt->pw;
-	struct sshbuf *b;
+	struct sshbuf *b = NULL;
 	struct sshkey *key = NULL;
-	char *pkalg, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
-	u_char *pkblob, *sig, have_sig;
+	char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
+	u_char *pkblob = NULL, *sig = NULL, have_sig;
 	size_t blen, slen;
 	int r, pktype;
 	int authenticated = 0;
 	struct sshauthopt *authopts = NULL;
 
-	if (!authctxt->valid) {
-		debug2("%s: disabled because of invalid user", __func__);
-		return 0;
-	}
 	if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
 	    (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
 	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
@@ -164,6 +160,11 @@ userauth_pubkey(struct ssh *ssh)
 				fatal("%s: sshbuf_put_string session id: %s",
 				    __func__, ssh_err(r));
 		}
+		if (!authctxt->valid || authctxt->user == NULL) {
+			debug2("%s: disabled because of invalid user",
+			    __func__);
+			goto done;
+		}
 		/* reconstruct packet */
 		xasprintf(&userstyle, "%s%s%s", authctxt->user,
 		    authctxt->style ? ":" : "",
@@ -180,7 +181,6 @@ userauth_pubkey(struct ssh *ssh)
 #ifdef DEBUG_PK
 		sshbuf_dump(b, stderr);
 #endif
-
 		/* test for correct signature */
 		authenticated = 0;
 		if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) &&
@@ -191,7 +191,6 @@ userauth_pubkey(struct ssh *ssh)
 			authenticated = 1;
 		}
 		sshbuf_free(b);
-		free(sig);
 		auth2_record_key(authctxt, authenticated, key);
 	} else {
 		debug("%s: test pkalg %s pkblob %s%s%s",
@@ -202,6 +201,11 @@ userauth_pubkey(struct ssh *ssh)
 		if ((r = sshpkt_get_end(ssh)) != 0)
 			fatal("%s: %s", __func__, ssh_err(r));
 
+		if (!authctxt->valid || authctxt->user == NULL) {
+			debug2("%s: disabled because of invalid user",
+			    __func__);
+			goto done;
+		}
 		/* XXX fake reply and always send PK_OK ? */
 		/*
 		 * XXX this allows testing whether a user is allowed
@@ -235,6 +239,7 @@ done:
 	free(pkblob);
 	free(key_s);
 	free(ca_s);
+	free(sig);
 	return authenticated;
 }
 
-- 
2.20.1