print out all known keys for a host if we get a unknown host key,

see discussion at http://marc.theaimsgroup.com/?t=101069210100016&r=1&w=4

the ssharp mitm tool attacks users in a similar way, so i'd like to
pointed out again:
	A MITM attack is always possible if the ssh client prints:
	The authenticity of host 'bla' can't be established.
(protocol version 2 with pubkey authentication allows you to detect
MITM attacks)

3 files changed, 109 insertions, 14 deletions

diff --git a/usr.bin/ssh/hostfile.c b/usr.bin/ssh/hostfile.c
index cefff8d6276..dcee0344833 100644
--- a/usr.bin/ssh/hostfile.c
+++ b/usr.bin/ssh/hostfile.c
@@ -36,7 +36,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: hostfile.c,v 1.29 2001/12/18 10:04:21 jakob Exp $");
+RCSID("$OpenBSD: hostfile.c,v 1.30 2002/07/24 16:11:18 markus Exp $");
 
 #include "packet.h"
 #include "match.h"
@@ -91,11 +91,14 @@ hostfile_check_key(int bits, Key *key, const char *host, const char *filename, i
  * in the list of our known hosts. Returns HOST_OK if the host is known and
  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
  * if the host is known but used to have a different host key.
+ *
+ * If no 'key' has been specified and a key of type 'keytype' is known
+ * for the specified host, then HOST_FOUND is returned.
  */
 
-HostStatus
-check_host_in_hostfile(const char *filename, const char *host, Key *key,
-    Key *found, int *numret)
+static HostStatus
+check_host_in_hostfile_by_key_or_type(const char *filename,
+    const char *host, Key *key, int keytype, Key *found, int *numret)
 {
 	FILE *f;
 	char line[8192];
@@ -105,8 +108,7 @@ check_host_in_hostfile(const char *filename, const char *host, Key *key,
 	HostStatus end_return;
 
 	debug3("check_host_in_hostfile: filename %s", filename);
-	if (key == NULL)
-		fatal("no key to look up");
+
 	/* Open the file containing the list of known hosts. */
 	f = fopen(filename, "r");
 	if (!f)
@@ -147,12 +149,20 @@ check_host_in_hostfile(const char *filename, const char *host, Key *key,
 		 */
 		if (!hostfile_read_key(&cp, &kbits, found))
 			continue;
-		if (!hostfile_check_key(kbits, found, host, filename, linenum))
-			continue;
 
 		if (numret != NULL)
 			*numret = linenum;
 
+		if (key == NULL) {
+			/* we found a key of the requested type */
+			if (found->type == keytype)
+				return HOST_FOUND;
+			continue;
+		}
+
+		if (!hostfile_check_key(kbits, found, host, filename, linenum))
+			continue;
+
 		/* Check if the current key is the same as the given key. */
 		if (key_equal(key, found)) {
 			/* Ok, they match. */
@@ -177,6 +187,24 @@ check_host_in_hostfile(const char *filename, const char *host, Key *key,
 	return end_return;
 }
 
+HostStatus
+check_host_in_hostfile(const char *filename, const char *host, Key *key,
+    Key *found, int *numret)
+{
+	if (key == NULL)
+		fatal("no key to look up");
+	return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
+	    found, numret));
+}
+
+int
+lookup_key_in_hostfile_by_type(const char *filename, const char *host,
+    int keytype, Key *found, int *numret)
+{
+	return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
+	    keytype, found, numret) == HOST_FOUND);
+}
+
 /*
  * Appends an entry to the host file.  Returns false if the entry could not
  * be appended.
diff --git a/usr.bin/ssh/hostfile.h b/usr.bin/ssh/hostfile.h
index 0244fdb53ea..06373242147 100644
--- a/usr.bin/ssh/hostfile.h
+++ b/usr.bin/ssh/hostfile.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: hostfile.h,v 1.10 2001/12/18 10:04:21 jakob Exp $	*/
+/*	$OpenBSD: hostfile.h,v 1.11 2002/07/24 16:11:18 markus Exp $	*/
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -15,12 +15,14 @@
 #define HOSTFILE_H
 
 typedef enum {
-	HOST_OK, HOST_NEW, HOST_CHANGED
+	HOST_OK, HOST_NEW, HOST_CHANGED, HOST_FOUND,
 }       HostStatus;
 
 int	 hostfile_read_key(char **, u_int *, Key *);
 HostStatus
 check_host_in_hostfile(const char *, const char *, Key *, Key *, int *);
 int	 add_host_to_hostfile(const char *, const char *, Key *);
+int	
+lookup_key_in_hostfile_by_type(const char *, const char *, int , Key *, int *);
 
 #endif
diff --git a/usr.bin/ssh/sshconnect.c b/usr.bin/ssh/sshconnect.c
index e642fa21b67..d042fbf59b5 100644
--- a/usr.bin/ssh/sshconnect.c
+++ b/usr.bin/ssh/sshconnect.c
@@ -13,7 +13,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: sshconnect.c,v 1.131 2002/07/12 13:29:09 itojun Exp $");
+RCSID("$OpenBSD: sshconnect.c,v 1.132 2002/07/24 16:11:18 markus Exp $");
 
 #include <openssl/bn.h>
 
@@ -42,6 +42,8 @@ extern char *__progname;
 extern uid_t original_real_uid;
 extern uid_t original_effective_uid;
 
+static int show_other_keys(const char *, Key *);
+
 /*
  * Connect to the given ssh server using a proxy command.
  */
@@ -489,7 +491,7 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
 	int local = 0, host_ip_differ = 0;
 	char ntop[NI_MAXHOST];
 	char msg[1024];
-	int len, host_line, ip_line;
+	int len, host_line, ip_line, has_keys;
 	const char *host_file = NULL, *ip_file = NULL;
 
 	/*
@@ -630,14 +632,19 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
 			    "have requested strict checking.", type, host);
 			goto fail;
 		} else if (options.strict_host_key_checking == 2) {
+			has_keys = show_other_keys(host, host_key);
 			/* The default */
 			fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX);
 			snprintf(msg, sizeof(msg),
 			    "The authenticity of host '%.200s (%s)' can't be "
-			    "established.\n"
+			    "established%s\n"
 			    "%s key fingerprint is %s.\n"
 			    "Are you sure you want to continue connecting "
-			    "(yes/no)? ", host, ip, type, fp);
+			    "(yes/no)? ",
+			     host, ip,
+			     has_keys ? ",\nbut keys of different type are already "
+			     "known for this host." : ".",
+			     type, fp);
 			xfree(fp);
 			if (!confirm(msg))
 				goto fail;
@@ -740,6 +747,9 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
 		 * accept the authentication.
 		 */
 		break;
+	case HOST_FOUND:
+		fatal("internal error");
+		break;
 	}
 
 	if (options.check_host_ip && host_status != HOST_CHANGED &&
@@ -851,3 +861,58 @@ ssh_put_password(char *password)
 	memset(padded, 0, size);
 	xfree(padded);
 }
+
+static int
+show_key_from_file(const char *file, const char *host, int keytype)
+{
+	Key *found;
+	char *fp;
+	int line, ret;
+
+	found = key_new(keytype);
+	if ((ret = lookup_key_in_hostfile_by_type(file, host,
+	    keytype, found, &line))) {
+		fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
+		log("WARNING: %s key found for host %s\n"
+		    "in file %s line %d with\n"
+		    "%s key fingerprint %s.",
+		    key_type(found), host, file, line,
+		    key_type(found), fp);
+		xfree(fp);
+	}
+	key_free(found);
+	return (ret);
+}
+
+/* print all known host keys for a given host, but skip keys of given type */
+static int
+show_other_keys(const char *host, Key *key)
+{
+	int type[] = { KEY_RSA1, KEY_RSA, KEY_DSA, -1};
+	int i, found = 0;
+
+	for (i = 0; type[i] != -1; i++) {
+		if (type[i] == key->type)
+			continue;
+		if (type[i] != KEY_RSA1 &&
+		    show_key_from_file(options.user_hostfile2, host, type[i])) {
+			found = 1;
+			continue;
+		}
+		if (type[i] != KEY_RSA1 &&
+		    show_key_from_file(options.system_hostfile2, host, type[i])) {
+			found = 1;
+			continue;
+		}
+		if (show_key_from_file(options.user_hostfile, host, type[i])) {
+			found = 1;
+			continue;
+		}
+		if (show_key_from_file(options.system_hostfile, host, type[i])) {
+			found = 1;
+			continue;
+		}
+		debug2("no key of type %d for host %s", type[i], host);
+	}
+	return (found);
+}