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] =?UTF-8?q?delay=20bailout=20for=20invalid=20authenticatin?=
 =?UTF-8?q?g=20user=20until=20after=20the=20packet=20containing=20the=20re?=
 =?UTF-8?q?quest=20has=20been=20fully=20parsed.=20Reported=20by=20Dariusz?=
 =?UTF-8?q?=20Tytko=20and=20Micha=C5=82=20Sajdak;=20ok=20deraadt?=
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Content-Type: text/plain; charset=UTF-8
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(-)

Index: openssh-7.6p1/auth2-gss.c
===================================================================
--- openssh-7.6p1.orig/auth2-gss.c	2019-03-12 14:38:32.420914340 +0100
+++ openssh-7.6p1/auth2-gss.c	2019-03-12 14:38:37.116940749 +0100
@@ -105,9 +105,6 @@ userauth_gssapi(struct ssh *ssh)
 	u_int len;
 	u_char *doid = NULL;
 
-	if (!authctxt->valid || authctxt->user == NULL)
-		return (0);
-
 	mechs = packet_get_int();
 	if (mechs == 0) {
 		debug("Mechanism negotiation is not supported");
@@ -138,6 +135,12 @@ 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);
Index: openssh-7.6p1/auth2-hostbased.c
===================================================================
--- openssh-7.6p1.orig/auth2-hostbased.c	2019-03-12 14:38:33.264919086 +0100
+++ openssh-7.6p1/auth2-hostbased.c	2019-03-12 14:38:37.116940749 +0100
@@ -67,10 +67,6 @@ 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 ||
@@ -117,6 +113,10 @@ userauth_hostbased(struct ssh *ssh)
 		    __func__, sshkey_type(key));
 		goto done;
 	}
+	if (!authctxt->valid || authctxt->user == NULL) {
+		debug2("%s: disabled because of invalid user", __func__);
+		goto done;
+	}
 
 	service = ssh->compat & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 	    authctxt->service;
Index: openssh-7.6p1/auth2-pubkey.c
===================================================================
--- openssh-7.6p1.orig/auth2-pubkey.c	2019-03-12 14:38:33.264919086 +0100
+++ openssh-7.6p1/auth2-pubkey.c	2019-03-12 14:38:37.120940772 +0100
@@ -77,18 +77,15 @@ static int
 userauth_pubkey(struct ssh *ssh)
 {
 	Authctxt *authctxt = ssh->authctxt;
-	struct sshbuf *b;
+	struct sshbuf *b = NULL;
 	struct sshkey *key = NULL;
-	char *pkalg, *userstyle = NULL, *fp = NULL;
-	u_char *pkblob, *sig, have_sig;
+	char *pkalg = NULL, *userstyle = NULL, *key_s = NULL;
+	char *fp = NULL;
+	u_char *pkblob = NULL, *sig = NULL, have_sig;
 	size_t blen, slen;
 	int r, pktype;
 	int authenticated = 0;
 
-	if (!authctxt->valid) {
-		debug2("%s: disabled because of invalid user", __func__);
-		return 0;
-	}
 	if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0)
 		fatal("%s: sshpkt_get_u8 failed: %s", __func__, ssh_err(r));
 	if (ssh->compat & SSH_BUG_PKAUTH) {
@@ -166,6 +163,11 @@ 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 ? ":" : "",
@@ -193,7 +195,6 @@ userauth_pubkey(struct ssh *ssh)
 #ifdef DEBUG_PK
 		sshbuf_dump(b, stderr);
 #endif
-
 		/* test for correct signature */
 		authenticated = 0;
 		if (PRIVSEP(user_key_allowed(authctxt->pw, key, 1)) &&
@@ -202,7 +203,6 @@ userauth_pubkey(struct ssh *ssh)
 			authenticated = 1;
 		}
 		sshbuf_free(b);
-		free(sig);
 		auth2_record_key(authctxt, authenticated, key);
 	} else {
 		debug("%s: test whether pkalg/pkblob are acceptable for %s %s",
@@ -210,6 +210,11 @@ 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
@@ -237,6 +242,7 @@ done:
 	free(userstyle);
 	free(pkalg);
 	free(pkblob);
+	free(sig);
 	free(fp);
 	return authenticated;
 }
