6477720 possible DoS in CRC compensation attack detector for SSH protocol 1

6481229 potential race in fatal_cleanup() in ssh

4 files changed, 41 insertions, 11 deletions

diff --git a/usr/src/cmd/ssh/include/deattack.h b/usr/src/cmd/ssh/include/deattack.h
index 22c088e603..fa7fc82312 100644
--- a/usr/src/cmd/ssh/include/deattack.h
+++ b/usr/src/cmd/ssh/include/deattack.h
@@ -32,6 +32,7 @@ extern "C" {
 /* Return codes */
 #define DEATTACK_OK		0
 #define DEATTACK_DETECTED	1
+#define DEATTACK_DOS_DETECTED	2
 
 int	 detect_attack(u_char *, u_int32_t, u_char[8]);
 
diff --git a/usr/src/cmd/ssh/libssh/common/deattack.c b/usr/src/cmd/ssh/libssh/common/deattack.c
index a5e5fde167..82afd4f16b 100644
--- a/usr/src/cmd/ssh/libssh/common/deattack.c
+++ b/usr/src/cmd/ssh/libssh/common/deattack.c
@@ -29,6 +29,24 @@ RCSID("$OpenBSD: deattack.c,v 1.18 2002/03/04 17:27:39 stevesk Exp $");
 #include "xmalloc.h"
 #include "deattack.h"
 
+/*
+ * CRC attack detection has a worst-case behaviour that is O(N^2) over
+ * the number of identical blocks in a packet. This behaviour can be 
+ * exploited to create a limited denial of service attack. 
+ * 
+ * However, because we are dealing with encrypted data, identical
+ * blocks should only occur every 2^35 maximally-sized packets or so. 
+ * Consequently, we can detect this DoS by looking for identical blocks
+ * in a packet.
+ *
+ * The parameter below determines how many identical blocks we will
+ * accept in a single packet, trading off between attack detection and
+ * likelihood of terminating a legitimate connection. A value of 32 
+ * corresponds to an average of 2^40 messages before an attack is
+ * misdetected
+ */
+#define MAX_IDENTICAL	32
+
 /* SSH Constants */
 #define SSH_MAXBLOCKS	(32 * 1024)
 #define SSH_BLOCKSIZE	(8)
@@ -89,7 +107,7 @@ detect_attack(u_char *buf, u_int32_t len, u_char *IV)
 	static u_int16_t *h = (u_int16_t *) NULL;
 	static u_int32_t n = HASH_MINSIZE / HASH_ENTRYSIZE;
 	u_int32_t i, j;
-	u_int32_t l;
+	u_int32_t l, same;
 	u_char *c;
 	u_char *d;
 
@@ -135,7 +153,7 @@ detect_attack(u_char *buf, u_int32_t len, u_char *IV)
 	if (IV)
 		h[HASH(IV) & (n - 1)] = HASH_IV;
 
-	for (c = buf, j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
+	for (c = buf, same = j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
 		for (i = HASH(c) & (n - 1); h[i] != HASH_UNUSED;
 		    i = (i + 1) & (n - 1)) {
 			if (h[i] == HASH_IV) {
@@ -146,6 +164,8 @@ detect_attack(u_char *buf, u_int32_t len, u_char *IV)
 						break;
 				}
 			} else if (!CMP(c, buf + h[i] * SSH_BLOCKSIZE)) {
+				if (++same > MAX_IDENTICAL)
+					return (DEATTACK_DOS_DETECTED);
 				if (check_crc(c, buf, len, IV))
 					return (DEATTACK_DETECTED);
 				else
diff --git a/usr/src/cmd/ssh/libssh/common/log.c b/usr/src/cmd/ssh/libssh/common/log.c
index 4042d2ffd9..296c52a3f1 100644
--- a/usr/src/cmd/ssh/libssh/common/log.c
+++ b/usr/src/cmd/ssh/libssh/common/log.c
@@ -33,7 +33,7 @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 /*
- * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
+ * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
@@ -45,6 +45,7 @@ RCSID("$OpenBSD: log.c,v 1.24 2002/07/19 15:43:33 markus Exp $");
 #include "log.h"
 #include "xmalloc.h"
 
+#include <atomic.h>
 #include <syslog.h>
 
 static LogLevel log_level = SYSLOG_LEVEL_INFO;
@@ -262,16 +263,15 @@ fatal_remove_all_cleanups(void)
 	fatal_cleanups = NULL;
 }
 
-/* Cleanup and exit */
+/* Cleanup and exit. Make sure each cleanup is called only once. */
 void
 fatal_cleanup(void)
 {
 	struct fatal_cleanup *cu, *next_cu;
-	static int called = 0;
+	static volatile u_int called = 0;
 
-	if (called)
+	if (atomic_cas_uint(&called, 0, 1) == 1)
 		exit(255);
-	called = 1;
 	/* Call cleanup functions. */
 	for (cu = fatal_cleanups; cu; cu = next_cu) {
 		next_cu = cu->next;
diff --git a/usr/src/cmd/ssh/libssh/common/packet.c b/usr/src/cmd/ssh/libssh/common/packet.c
index 10cf9bdc1b..10fbdd0895 100644
--- a/usr/src/cmd/ssh/libssh/common/packet.c
+++ b/usr/src/cmd/ssh/libssh/common/packet.c
@@ -36,7 +36,7 @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 /*
- * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
+ * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
@@ -913,9 +913,18 @@ packet_read_poll1(void)
 	 * (C)1998 CORE-SDI, Buenos Aires Argentina
 	 * Ariel Futoransky(futo@core-sdi.com)
 	 */
-	if (!receive_context.plaintext &&
-	    detect_attack(buffer_ptr(&input), padded_len, NULL) == DEATTACK_DETECTED)
-		packet_disconnect("crc32 compensation attack: network attack detected");
+	if (!receive_context.plaintext) {
+		switch (detect_attack(buffer_ptr(&input), padded_len, NULL)) {
+		case DEATTACK_DETECTED:
+			packet_disconnect("crc32 compensation attack: "
+			    "network attack detected");
+			break;
+		case DEATTACK_DOS_DETECTED:
+			packet_disconnect("deattack denial of "
+			    "service detected");
+			break;
+		}
+	}
 
 	/* Decrypt data to incoming_packet. */
 	buffer_clear(&incoming_packet);